1 Foreword This Exam Preparation book is intended for those preparing for the Certified Wireless Network Administrator Exam. The Art of Service is an Accredited Training Organization and has been training IT professionals since 1998. The strategies and content in this book are a result of experience and understanding of the Certified Wireless Network Administrator methods, and the exam requirements. This book is not a replacement for completing the course. This is a study aid to assist those who have completed an accredited course and are preparing for the exam. Do not underestimate the value of your own notes and study aids. The more you have, the more prepared you will be. While it is not possible to pre-empt every question that may be asked in the exam, this book covers the main concepts covered within the Certified Wireless Network Administrator discipline. The Certified Wireless Network Administrator (CWNA) is a foundation level certification that measures the ability to administer any wireless LAN. The exam covers a wide range of wireless LAN topics and is directed toward professionals who want to work with 802.11 wireless technology, rather than vendor-specific products. The CWNA certification demonstrates a candidate’s ability to successfully administer enterprise-class wireless LANS. Due to licensing rights, we are unable to provide actual CWNA Exams. However, the study notes and sample exam questions in this book will allow you to more easily prepare for a CWNA exam. Ivanka Menken Executive Director The Art of Service
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2 Table of Contents 1 2 3 4 5 6
Foreword ............................................................................ 1 Table of Contents............................................................... 3 Certified Wireless Network Administrator........................... 7 Exam Specifics .................................................................. 8 Exam Prerequisites ............................................................ 8 Understanding Wireless LANs ........................................... 9 6.1 The Evolution of Wireless LANs................................... 9 7 Fundamentals of Radio Frequency (RF) .......................... 12 7.1 How Radio Frequencies Work ................................... 12 7.2 VSWR – Voltage Standing Wave Ratio ..................... 14 7.3 Understanding Antennas ........................................... 15 7.4 Measuring Radio Frequencies ................................... 16 8 Spread Spectrum Technology ......................................... 18 8.1 Communication Types ............................................... 18 8.2 Wireless LANs ........................................................... 19 8.3 Frequency Hopping Spread Spectrum (FHSS) .......... 21 8.4 Direct Sequence Spread Spectrum (DSSS) .............. 23 9 Wireless LAN Organizations and Standards .................... 27 9.1 Federal Communications Commission (FCC) ............ 27 9.2 Institute of Electrical and Electronics Engineers (IEEE) 31 9.3 Major Organizations ................................................... 34 9.4 Competing Technologies ........................................... 36 10 Infrastructure Devices for Wireless LANs ........................ 39 10.1 Access Points ......................................................... 39 10.2 Wireless Bridges ..................................................... 42 10.3 Wireless Workgroup Bridges .................................. 43 10.4 Wireless LAN Client Devices .................................. 44 10.5 Wireless Residential Gateways .............................. 47 10.6 Enterprise Wireless Gateways ................................ 48 11 Antennas and Accessories .............................................. 51 11.1 Radio Frequency Antennas .................................... 51 11.2 Concepts of RF Antennas....................................... 53 11.3 Antenna Installation ................................................ 56 Copyright The Art of Service Brisbane, Australia │ Email:
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11.4 Power over Ethernet (PoE) Devices ....................... 59 11.5 Accessories for Wireless LAN ................................ 62 12 802.11 Network Architecture ............................................ 70 12.1 Identifying Wireless LANs ....................................... 70 12.2 Authentication and Association ............................... 74 12.3 Authentication Methods .......................................... 75 12.4 Emerging Authentication Protocols ......................... 77 12.5 Service Sets ........................................................... 80 12.6 Roaming ................................................................. 82 12.7 Power Management Features ................................ 85 13 MAC and Physical Layers ................................................ 87 13.1 Communicating with Wireless LANs ....................... 87 13.2 Interframe Spacing ................................................. 92 13.3 RTS/CTS ................................................................ 95 13.4 Modulation .............................................................. 96 14 Troubleshooting Wireless Installations............................. 98 14.1 Multipath ................................................................. 98 14.2 Hidden Node ......................................................... 102 14.3 Near/Far ............................................................... 103 14.4 System Throughput .............................................. 104 14.5 Co-location Throughput ........................................ 105 14.6 Types of Interference ............................................ 106 14.7 Range Considerations .......................................... 109 15 Wireless LAN Security ................................................... 111 15.1 Wired Equivalent Privacy ...................................... 111 15.2 Wireless LAN Attacks ........................................... 114 15.3 Securing Wireless LANs ....................................... 115 16 Fundamentals of Site Surveying .................................... 117 16.1 Understanding Site Surveys ................................. 117 16.2 Site Survey Preparation ........................................ 118 16.3 Site Survey Equipment ......................................... 120 16.4 Conducting Site Surveys ...................................... 120 17 Practice Exam ................................................................ 123 17.1 Questions ............................................................. 123 18 Answer Guide ................................................................ 134 18.1 Answers ................................................................ 134 19 References .................................................................... 140 Copyright The Art of Service Brisbane, Australia │ Email:
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Notice of Rights All rights reserved. No part of this book may be reproduced or transmitted in any form by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Notice of Liability The information in this book is distributed on an “As Is” basis without warranty. While every precaution has been taken in the preparation of the book, neither the author nor the publisher shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the instructions contained in this book or by the products described in it. Trademarks Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations appear as requested by the owner of the trademark. All other product names and services identified throughout this book are used in editorial fashion only and for the benefit of such companies with no intention of infringement of the trademark. No such use, or the use of any trade name, is intended to convey endorsement or other affiliation with this book.
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3 Certified Wireless Network Administrator Certified Wireless Network Administrator is the foundation level certification for CWNP. It is actually the second exam in the four-level certification process. The main subject areas dealt with by the CWNA exam are: Wireless Standards and Organization Radio Technologies Antennas Wireless LAN Hardware and Software Network Design 802.11 Network Architecture Wireless LAN security Troubleshooting Site Surveys. The CWNA certification is valid for three years, and can be renewed by retaking the test or moving to the next level in the certification path.
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4 Exam Specifics Exams cost $175 at time of printing. Duration – 90 minutes 60 questions Question Type – Multiple-choice / Multiple answer Passing Score – 70% Registration of the exam must be made with Pearson VUE.
5 Exam Prerequisites There are no prerequisites for the Certified Wireless Network Administrator exam.
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6 Understanding Wireless LANs 6.1
The Evolution of Wireless LANs
Wireless LANs began as a military technology, providing a simple method of exchanging data that could be implemented easily in a combat environment. At first, the cost of the technology was enormous. As the cost decreased, enterprises began to integrate wireless capabilities into their network architecture. The driving force for most enterprises was providing an inexpensive way to connect campus environments. As the cost continued to decrease and quality increased, the mobility aspects of wireless computing became advantageous for businesses. In addition, households started to adopt wireless technologies in home offices and wireless gaming stations. While this growth continued, the need for standards between different manufacturers and installed LANS also grew. Stress on compatibility of systems and interoperability between networks became key issues. 6.1.1
Wireless LAN Standards
Wireless LANs transmit radio frequencies and are regulated by the same type of laws governing AM/FM radios. In the United States, the Federal Communications Commission (FCC) regulates the use of wireless LAN devices. The Institute of Electrical and Electronic Engineers (IEEE) have created and currently maintain several operational standards. The current IEEE standards: 802.11 is the original LAN standard and specifies the lowest data transfer rates for both radio frequencies and light-based transmissions. 802.11b has faster data transfer rates and has been promoted to great extent as Wi-Fi by the Wireless Ethernet Copyright The Art of Service Brisbane, Australia │ Email:
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Compatibility Alliance (WECA). 802.11a uses 5GHz UNII frequency bands. It is much faster than 802.11b but is not compatible with that standard. 802.11g has data transfer rates as fast as 802.11a and is backwards compatible to 802.11. 802.11-2007, also referred to as 802.11REVma, was an effort to create a single document out of the original 1999 standard and all 8 of its amendments.
New standards are always being proposed and take years to adopt. Some standards, such as 802.11g, are in such high demand that they are adopted before the standard is finalized. Another standard, called OpenAir, was created by the Wireless LAN Interoperability Forum (WLIF) to assist manufacturers in interoperability testing. 6.1.2
Uses of Wireless LANs
Wireless LANs provide another point of access to a wired network. Like other access methods, wireless LANs are data-link layer networks and implemented in the access layer role. Unlike other access methods, wireless solutions increase the mobility of an organization. Due to problems with speed and resiliency, wireless networks are not usually implemented in distribution or core roles in an organization. Wireless allows the extension of a wired network, specifically when using wired solutions would be cost-prohibitive. Seamless connectivity to remote areas within a building can allow employees to gain and maintain access, even when moving. Two wired networks can be connected using cost-effective wireless connections. Point-to-point (PTP) connectivity speaks to the wireless connection between two buildings and will use semi-directional or highly directional antennas at both ends. Point-to-multipoint (PTMP) solutions typically connect three or more buildings in a hub/spoke fashion. Omni-directional antennas are installed at the hub, with Copyright The Art of Service Brisbane, Australia │ Email:
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semi-directional antennas at each of the spokes of the network. All residential businesses and families rely on services provided by a telecommunications or cable company. Wireless solutions have increased the availability of these services to customers by providing low-cost “last mile” connectivity. The term, “last mile,” refers to the connectivity between the customer and the central office of the service provider. The connection can be wired or wireless. For a few customers such as rural or hard to reach locations, a wireless solution is the only option available. Wireless LANS provide the best option for users and organizations interested in maintaining little or almost no infrastructure, and to raise the mobility capabilities of the user.
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7 Fundamentals of Radio Frequency (RF) 7.1
How Radio Frequencies Work
Radio frequencies are high frequency alternating current (AC) signals. They are passed through a copper conductor then radiated into the air through an antenna. The antenna will take a wireless signal and convert it into a wired signal, as well as reversing the process. The signal moves (propagates) from the antenna, or source, in a straight line is all directions. 7.1.1
Behaviors of Radio Waves
The basic behaviors of radio frequencies of importance include: Gain Loss Reflection Refraction Diffraction Scattering. 7.1.2
Gain
Gain refers to an increase in a radio frequency's signal amplitude. Typically, the amplitude changes from an external power source, such as an RF amplifier, making frequency gain an active process. However, there is a passive process of reflecting, or bouncing, a signal to increase the signal's strength. 7.1.3
Loss
Loss is a decrease in signal strength. Loss of a signal is possible within a wire and as a radio signal. Some of the reasons for signal loss include: Resistance of cables and connectors Copyright The Art of Service Brisbane, Australia │ Email:
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Mismatch or impedance which can reflect signals back Obstacles which can absorb, reflect, or destroy signals An RF attenuator is intentionally used to convert high frequency AC to heat.
Wireless devices which read signals have a sensitivity threshold. This threshold is the point where the device can distinguish a signal from mere background noise. 7.1.4
Reflection
Reflection happens when a propagated electromagnetic wave bounces off a large object of high density, such as the earth, buildings, walls, etc. The smoother the surface of the object, the more intact the signal remains, except for some absorption that may occur. The rougher the surface, the more likely the reflected signal becomes multipathed. This multipath effect can severely degrade the signal and requires antenna diversity to compensate for it. 7.1.5
Refraction
Where reflection bounces off of high density objects, refraction, or bending of the signal, happens when the signal hits an object of medium density. In truth, the signal is typically reflected and refracted. The refraction will go through the object, but its direction has changed. Refraction is a consideration for long distance RF links. Atmospheric conditions are primary causes for refraction. 7.1.6
Defraction
When a radio wave between a transmitter receiver is obstructed, how the signal reacts is dependent on the geometry of the object and the amplitude, phase, and polarization of the wave at the point of impact. Besides refection and refraction, the signal may be diffracted, or bend around the object. Strictly speaking, diffraction is the slowing of the wave at the point of impact while the rest of the wave maintains the same speed. The higher the frequency, the greater the defraction. Copyright The Art of Service Brisbane, Australia │ Email:
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7.1.7
Scattering
Signals can also be scattered and this is the result of obstructions with a rough surface or irregularities in the signal path, such as foliage, street signs, or furniture. Scattering happens when a wave hits an uneven surface and reflects in multiple directions simultaneously. Dust clouds or rainstorms can be enough to reflect and refract a signal to cause scattering to the point where transmissions are severely degraded or lost.
7.2
VSWR – Voltage Standing Wave Ratio
Impedance is the resistance to current flow measured in Ohms. When the signal is reflected, the point of impedance is mismatched in the signal path creating a VSWR (Voltage Standing Wave Ratio). Some power is reflected back towards the transmitter resulting in loss of forward energy, called the return loss. VSWR shows then the impedance of the ends of a connection vary and the maximum amount of the transmitted power is not received at the antenna. VSWR is expressed as a relationship between two numbers, shown as x:1. The second number will always be one and represents a perfect impedance match. The first number represents an imperfect impedance match and the closer it is to one, the better the impedance matching available to the system. 7.2.1
Impact of VSWR
The more mismatched the VSWR is, the more problems with the RF circuit. In most cases, the amplitude of the RF signal is decreased. However, when transmitters are not protected against returned power, the electronics of the transmitter can burn out. Preventative measures against VSWR include: Tight connections between cables and connectors Use of impedance matched hardware Use of high-quality equipment capable of being calibrated. Copyright The Art of Service Brisbane, Australia │ Email:
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7.3
Understanding Antennas
Transmitting antennas convert electrical energy into radio frequency waves. Receiving antennas convert radio frequency waves into electrical energy. The frequency of the signal that an antenna can transmit or receive propagated waves is dependent on the physical dimensions of the antenna. Some concepts about antenna pertinent to wireless LANs include: Line of Sight (LOS) The Fresnel Zone Antenna Gain. 7.3.1
Line of Sight
A visual line of sight is the straight line between an object in view, or transmitter, and the observer, or receiver. With radio waves, the effects of reflection, refraction, and diffraction have some impact on how straight the line of sight remains. 7.3.2
Frensel Zone
The RF line of sight can be changed by the diffraction and reflection of the signal by objects blocking or degrading the signal. The objects of concern are present in the Frensel Zone, an area around the line of sight which can introduce RF signal interference when blocked. The Fresel Zone can be viewed as a series of concentric ellipsoid-shaped areas around the LOS path. Some blockage within the Fresnel Zone can occur without any disruption to the link. Specifically, 20%-40% blockage in the zone will introduce little or no interference at all.
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7.3.3
Antenna Gain
A signal can be conditioned, amplified, and manipulated by an antenna. When none of this exists, the antenna element is considered passive. Amplification of the signal can be obtained by the physical characteristics of the antenna. An omni-directional antenna has a 360-degree horizontal beamwidth. A beamwidth is a measuring of the focused radiation in horizontal and vertical degrees. By limiting the beamwidth, the radio waves can be radiated further. Intentional radiators and Equivalent Isotropically Radiated Power (EIRP) are key considerations in understanding the power considerations of antennas. The FCC defines an intentional radiator as an RF device that is designed to generate and radiate RF signals. Each component of the hardware used by and connected to the intentional radiator has an impact on the power used by the radiator. The power output is actually regulated by the FCC, so it is important to understand how power is measured, how much power is allowed, and how to calculate these values. Equivalent Isotropically Radiated Power (EIRP)is the term for the power radiated by the antenna element. EIRP is regulated by the FCC and is used to calculate the viability of a wireless link.
7.4
Measuring Radio Frequencies
In calculating power for wireless LANs, the areas of concern are: Power at the transmitting device The loss and gain of connectivity devices, such as cables, connectors, amplifiers, attenuators, and splitters, between the transmitting device and the antenna Power at the intentional radiator Power (EIRP) at the antenna element.
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7.4.1
Units of Measure
The basic unit of power is watt (W). Defined as one ampere (A) of electrical current at one volt (V). A typical 120-volt night light is about 7 watts and can be seen 50 miles away on a clear night. The FCC requires that only 4 watts of power be radiated from an antenna in point-to-multipoint wireless LANs. Power levels for most wireless LANs are measured in milliwatts, or 1/1000 watt. Milliwatts are abbreviated as “mW.” A single LAN segment is typically no more than 100mW and will communicate up to half a mile in the best conditions. 7.4.2
Relative Measurements
A receiver can pick up radio signals as small as 0.000000001 W. This number is so small, that a logarithmic relationship is often used to communicate power of a signal, referred to as decibel (dB). Power loss and gain is measure in decibels. Some important numbers used by an administrator include: -3 dB = half the power in mW 3 dB = double the power in mW -10 dB = one tenth the power in mW 10 dB = ten times the power in mW The mathematical notation, dBm, refers to the reference point between the logarithmic dB scale and the linear watt scale, represented by: 1 mW = 0 dBm The mathematical notation, dBi, refers to the gain of an antenna. The “i” stands for “isotropic” which is a change in power referenced against an isotropic radiator. An isotropic radiator refers to a theoretical ideal transmitter which produces useful electromagnetic field output in all directions with equal intensity and used to measure output power, or EIRP. 1 W + 10 dBi = 10 W
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8 Spread Spectrum Technology Spread spectrum is a communications technique with a wide bandwidth and low peak power. It is hard to detect, which prevents it from being intercepted and demodulated without the right equipment.
8.1
Communication Types
8.1.1
Narrow Band Transmission
The precursor to spread spectrum communication is narrowband transmissions. Narrowband refers to a communication technology that uses only enough of the frequency spectrum to support the data signal. To send a transmission over such a small frequency range, a great deal of power is required. This is required to overcome the noise floor, or the general level of noise inherent in all transmissions. Narrowband transmissions can be intentionally overpowering a transmission using unwanted signals on the same band, or jammed. Additionally, noise on the same frequency or another signal can interrupt the transmission. 8.1.2
Spread Spectrum Transmission
Requirements required to be considered spread spectrum: The bandwidth of the signal must be wider than needed to send information The peak power needed to send the signal must be low. It has noise-like characteristics which prevents transmissions from being jammed or corrupted.
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8.2
Wireless LANs
8.2.1
Uses of Spread Spectrum
Spread spectrum communication has been used for: Military Cordless telephony Digital cellular telephony (CDMA) Personal communications system (PCS) Global positioning (GPS) Wireless LAN Bluetooth (WPAN). Wireless networks are available in several architectures: Wireless local area network (WLAN) Wireless personal area network (WPAN) Wireless metropolitan area network (WMAN) Wireless wide area network (WWAN). Spread spectrum is used differently in each of the architectures. 8.2.2
Same Rules, Different Technologies
Wireless LANs are used: To provide connectivity for mobile users within a building As a bridge between buildings across a campus setting. The most common use of spread spectrum technologies is the combination of WLANs and Bluetooth devices. WLANS are IEEE 802.11 compliant. Bluetooth devices are IEEE 802.15 compliant. Bluetooth and WLANs function differently, work within the same FCC rules, and interfere with each other. But much effort has been put towards research, time, and resources to have the two technologies coexist.
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8.2.3
Frequency Hops
WPANs, or its common name Bluetooth, is specified by the 802.15 standard. The regulation is broad, allowing for different types of spread spectrum uses. Frequency hopping is the act of jumping from one frequency to another within a frequency band while transmitting data. Bluetooth devices hop approximately 1600 times per second. HomeRF technology hop approximately 50 times per second. 802.11 WLANs hop 5-10 times per second. 8.2.4
Licensed Frequencies
WMANs are networks that consist of several high-power point-topoint wireless links across a city. WMANS use licensed frequencies. WLANs use unlicensed frequencies. The purpose of licensing a frequency is to ensure that the wireless network can be implemented without concern of a conflicting implementation elsewhere. Wireless Wide Area Networks also utilize licensed frequencies. 8.2.5
Specifications from the FCC
Two types of spread spectrum technologies are specified by the FCC: Direct sequence spread spectrum (DSSS) Frequency hopping spread spectrum (FHSS). The specific regulation is a collection of laws found in the Codes of Federal Regulation (CFR), volume 47 “Telegraphs, Telephones, and Radiotelegraphs,” part 15. Wireless LAN devices are sometimes called “part 15 devices” for this reason. Copyright The Art of Service Brisbane, Australia │ Email:
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8.3
Frequency Hopping Spread Spectrum (FHSS)
Frequency agility refers to the ability to abruptly change transmission frequency within a usable RF frequency band. FHSS uses frequency agility to spread data over 83 MHz of the usable 2.4 Ghz ISM. 8.3.1
How It Works
Hops, or frequency changes, in FHSS systems occur based on a pseudorandom sequence. The sequence is actually a list of several frequencies which will be hopped at specific times before the pattern is repeated. The time that a carrier sits at a specific frequency is called dwell time. The time it takes a carrier to complete a single hop is called hop time. The receiving device is synchronized to the hop sequence of the transmitting device to receive the signal properly. Narrow band interference can still interfere with the signal of frequency hopping systems. However, the interference only affects the frequency that is shared between the narrow band device and the frequency hopping device. The rest of the signal will remain intact and the lost data would be transmitted again. 8.3.2
Systems Using Frequency Hopping
The regulations of the FCC provide confines to use technologies such as frequency hopping. The IEEE creates operating standards within those confines. In regards to FHSS, IEEE standards describe FHSS systems based on: What frequency bands are allowed The hop sequences Dwell times Data rates. Copyright The Art of Service Brisbane, Australia │ Email:
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Frequency hopping systems must operate in the 2.4 Ghz ISM band. IEEE 802.11 specifies data rates of 1 Mbps and 2 Mbps. The 2.4 Ghz ISM band is defined by the FCC to be between 2.4000 Ghz and 2.5000 Ghz. Specific hop patterns are called channels. Typical frequency hopping systems use the 26 standard hop patterns as defined by the FCC or subsets of those patterns. Some systems will allow the creation of custom hop patterns. Some systems will allow synchronization between systems in a colocated environment to eliminate any collisions. Up to 79 synchronized, co-located access points is possible, though rather expensive. Recommendations generally prescribe a maximum of 12 co-located systems, though the use of non-synchronized devices can raise the number to 26 for medium-traffic networks. More traffic on the network will reduce the limit. The dwell time is the time a system transmits on a specific frequency. When that time expires, the system transmits on a different frequency. Times are typically measured in milliseconds (ms). The maximum dwell time defined by the FCC is 400 ms in any 30 second time period. When frequencies change within a system, it does so by: Switching to a different circuit tuned to a new frequency Using a different element in the current circuit. The change must complete before transmissions continue. Electrical latencies in the circuit will delay the time required to make the change. Hop times are measured in microseconds. The typical hop time for 802.11 FNSS systems is 200-300 microseconds. Data throughput has a correlation with the length of the dwell and hop times, namely, the longer dwell time will result in greater throughput. Copyright The Art of Service Brisbane, Australia │ Email:
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8.4
Direct Sequence Spread Spectrum (DSSS)
DSSS is the most commonly known and used spread spectrum type with most wireless LAN equipment using the technology. The type sends data where the transmission and receipt of the data are both using a 22 Mhz-wide set of frequencies. 8.4.1
How It Works
The data signal at a transmitting station is combined with a higher data rate bit sequence. The data rate bit sequence is referred to as a chipping code or processing gain. The signal's resistance to interference is increased when the processing gain increases. Most commercial products operate under 20. The FCC allows a minimum processing gain of 10 and the IEEE 802.11 has set the minimum at 11. The direct sequence starts with a carrier being modulated with a code sequence. The code has a specified number of “chips” that aid in determining the data rate, specifically: Number of chips per bit The speed of the code in chips/sec. 8.4.2
Direct Sequence Systems
IEEE specifications for the 2.4 Ghz ISM band include: For 802.11 devices – 1 or 2 Mbps data rate For 802.11b devices – 5.5 or 11 Mbps data rates For 802.11g devices – 54 Mbps data rate. Devices adhering to 802.11a operate on 5 Ghz UNII bands. DSSS systems use channels, but unlike FHSS systems are not defined using hop sequences. Each channel is a contiguous band of frequencies 22 Mhz wide with a 1 Mhz carrier frequency similar to FHSS. Copyright The Art of Service Brisbane, Australia │ Email:
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Channels overlap one another. The expression of a channel is by its band mean. Channel one is 2.412 Ghz represents a band from 2.401 GHz to 2.423 Ghz, or 2.412 Ghz ± 11 Mhz. Only 11 non-licensed channels are specified by the FCC. Their European counterpart, ETSI, specifies 9 channels. A complete list includes: Channe l ID
FCC ETSI Channel Channel Frequencie Frequencie s GHz s GHz
1
2.412
n/a
2
2.417
n/a
3
2.422
2.422
4
2.427
2.427
5
2.432
2.432
6
2.437
2.437
7
2.442
2.442
8
2.447
2.447
9
2.452
2.452
10
2.457
2.457
11
2.462
2.462
Using DSSS systems with overlapping channels in the same physical space will cause interference. Co-location of channels should happen if the channels are at least five apart, i.e. 1 and 6, 2 and 7, and so on. A maximum of three co-located channels are available, namely using 1, 6, and 11. Since the DSSS band is smaller than FHSS systems, they are more sensitive to narrow band interference. Additionally, since no frequency hopping is present with DSSS, the information is transmitted across the entire band. Still, DSSS uses a wide band and are highly resistant to any interference from narrow band transmissions. Copyright The Art of Service Brisbane, Australia │ Email:
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8.4.3
Comparing FHSS and DSSS
The factors used to compare FHSS and DSSS are: Narrow band interference Co-location Cost Equipment compatibility and availability Data rate and throughput Security Standards support. FHSS utilizes 79 Mhz-wide bands while DSSS uses 22 Mhz. This allows FHSS to be more resistant to narrow band interference. DSSS costs less than FHSS systems. Frequency hopping allows FHSS to use 79 discrete channels over the 3 channels available for DSSS. This provides an advantage to FHSS for co-located access points. Unfortunately in order to get the same throughput from both configuration, a FHSS solution would require 16 access points over the DSSS maximum 3 access points. Compatibility for DSSS equipment is widespread; being the focus on of the interoperability standard called Wireless Fidelity, or Wi-Fi, by the Wireless Ethernet Compatibility Alliance (WECA). Numerous tests are available to ensure devices are “Wi-Fi” compliant. Though FHSS adheres to the standards of 802.11, there are no compatibility tests available. FHSS systems which are compliant to 802.11 or OpenAir will have a data rate of no greater than 2 Mbps. The data throughput for both FHSS and DSSS systems is typically half the data rate. However, determining the data throughput has to take into consideration the power output: HomeRF devices utilize 125 mW of power compared to the single watt of 802.11 systems. Despite the ability to hop frequencies, FHSS systems are not secure for a number of reasons: To promote products effectively, manufacturers have to adhere to 802.11 or OpenAir standards. Copyright The Art of Service Brisbane, Australia │ Email:
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A standard set of hop sequences come from a predetermined list. Each beacon used will broadcast the channel number and the MAC address which can be easily determined with a spectrum analyzer.
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9 Wireless LAN Organizations and Standards Understanding the basis of the standards developed for wireless LANs ensures that the wireless solutions remain compatible within the network and for use with our wireless devices.
9.1
Federal Communications Commission (FCC)
The FCC is an independent government agency of the United States. Established by Congress through the Communications Act of 1934, the FCC is accountable for regulating interstate and international communications using radio, television, wire, satellite, and cable technologies. Their jurisdiction covers the 50 states, the district of Columbia and all U.S. possessions. Wireless LAN solutions must operate by laws made by the FCC. Specifically, the FCC regulates: Where on the radio frequency spectrum wireless LAN devices must operate The power utilization of wireless devices The transmission technologies used How and where various wireless LAN equipment can be used. 9.1.1
License-Free Bands
The limits on the frequency spectrum and power used by wireless LANs is one of the most significant regulations by the FCC. Wireless LANS can use the Industrial, Scientific, and Medical (ISM) bands. These bands are license free. Their locations start at 902 Mhz, 2.4 Ghz, and 5.8 Ghz. The widths of the bands vary from 26 Mhz to 150 Mhz. Three Unlicensed National Information Infrastructure (UNII) bands are specified by the FCC. These UNII bands are in the 5 Ghz range and 100 Mhz wide. These bands are also license free. Copyright The Art of Service Brisbane, Australia │ Email:
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Implementing wireless systems on license-free bands holds no requirement to petition the FCC for bandwidth or power needs. Though limits do exist, no permission is needed to transmit at these limits. Additionally, a no license, no cost policy is associated with licensing. It is within the license-free environment of ISM and UNII bands that allow small businesses and households to utilize wireless capabilities and encourages wireless LAN market growth. The freedom provided by license-free bands comes with drawbacks. Since multiple users can utilize the same license-free band, it can cause possible interference when two LAN segments are installed near each other. This is particularly present in residential implementations. Additionally, if one installation has a higher-power system, it could “white out” the wireless traffic of the other wireless LAN installation. This is a simple disabling of wireless LAN traffic, and the two systems do not have to be on the same channel or same spread spectrum technology. 9.1.2
Industrial Scientific Medical (ISM) Bands
The three license-free ISM bands specified by the FCC include: 900 MHz 2.4 Ghz 5.8 Ghz The 900 MHz ISM band represents the range of frequencies between 903 MHz to 928 MHz, or 915 MHz ± 13 MHz. Though widely used for wireless LAN solutions, this band has been abandoned in favor of higher frequency bands. Some wireless home phones and wireless camera systems still use the band. Replacement of obsolete equipment supporting the 900 MHz is quite expensive. Support of older 900 MHz units is difficult to obtain. Copyright The Art of Service Brisbane, Australia │ Email:
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The most populated space of the three ISM bands is the 2.4 GHz ISM band. The range of frequencies for this band is 2.4000 GHz - 2.5000 GHz, or 2.45000 GHz ± 50 MHz. Wireless LANs utilize only 100 MHz of the band, particularly 2.4000 – 2.4835 GHz. This applies to all devices complaint to 802.11, 802.11b, and 802.11g. The limitation is in place because the FCC has only specified power output for this range of frequencies. Growing in popularity is the 5 GHz ISM band, specifically 150 MHz bandwidth ranging from 5.725 GHz - 5.875 GHz. This ISM band is confusing because it is not specified for use by wireless LAN devices, but overlaps with the 5 GHz Upper UNII band which is specified for use by wireless LANs. 9.1.3
Unlicensed National Information Infrastructure (UNII) Bands
The 5 GHX UNII bands are comprised of thee 100 MHz-wide bands used by 802.11a-compliant devices. The three bands are known as lower, middle, and upper bands. The lower band is specified for indoor use. The upper band is specified for outdoor use. The middle band can be used indoors or outdoors. Each of these three bands has four non-overlapping DSSS channels separated by 5 MHz. Since most access points are mounted indoors, these bands allow for 8 non-overlapping access points by using both the lower and middle UNII bands. The lower band range is 5.15 GHz - 5.25 GHz and has a maximum output power of 50 mW specified by FCC. The IEEE has specified 40 mW as the maximum output power for 802.11a-compliant radios. These reserve the lower band for indoor operation only. The middle UNII band range is 5.25 - 5.35 GHz. The specified power output by the FCC is 250 mW: by the IEEE, 200 mW. This power limit allows operation of devices indoors and outdoors. The band is often used to handle short outdoor hops between closely spaced buildings. Copyright The Art of Service Brisbane, Australia │ Email:
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The upper band is reserved for outdoor links and has a FCC power output of 1 Watt (1000 mW). The IEEE limits the power output to 800 mW. The frequency range for the upper band is from 5.725 GHz 5.825 GHz. These limitations are still excellent for installing wireless LANs for large campuses and long-distance RF links. 9.1.4
Power Output
FCC regulations regarding power radiated from antenna elements is dependent on the use of point-to-multipoint (PtMP) or point-to-point (PtP) implementations. Power radiated by the antenna is called Equivalent Isotropically Radiated Power (EIRP). PtMP links are typically configured as a hub-n-spoke topology. In this topology, a central point of connection is typically in place and may or may not be supported by an omni-directional antenna. If the network is, the FCC automatically considers the link a PtMP link. The EIRP of a PtMP is limited by the FCC to 4 Watts in either the 2.4 GHz ISM band and 5 GHz UNII band. The intentional radiator which transmits the RF signal has a power limit of 1 Watt (+30 dBm). The FCC regulates that for every 3 dBi above the antenna's initial dBi of gain, the power of the intentional radiator must be reduced by the appropriate dB below the initial dBi. Simply, the EIRP of a PtMP is set. The power and gain of the antenna and intentional radiator can be used in combination to meet the limit. A PtMP Power Compensation Table shows most common combinations: Power at Antenna (dBm)
Antenna EIRP (dBm) Gain (dBi)
EIRP (watts)
30
6
36
4
27
9
36
4
24
12
36
4
21
15
36
4
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18
18
36
4
15
21
36
4
12
24
36
4
Point-to-Point (PtP) links have a single directional transmitting antenna and a single directional receiving antenna. TMP implementation, PtP have a sliding power limit. The FCC mandates that for every 3 dBi above the initial 6 dBi of antenna gain, the power at the intentional radiator must be reduced by 1 dB below the+30 dBm. A similar compensation table for PtP shows common combinations: Power at Antenna (dBm)
9.2
Antenna EIRP (dBm) Gain (dBi)
EIRP (watts)
30
6
36
4
29
9
38
6.3
28
12
40
10
27
15
42
16
26
18
44
25
25
21
46
39.8
24
24
48
63
23
27
50
100
22
30
52
158
Institute of Electrical and Electronics Engineers (IEEE)
When it comes to information technology in the United States, the IEEE is the primary standards creator for most subjects. They utilize the laws created by the FCC as guidelines to create standards. IEEE 802.11 is the recognized technology standard for wireless LANs. The standard consists of a main body and several amendments. The most referenced parts of the standard include: 802.11 Copyright The Art of Service Brisbane, Australia │ Email:
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9.2.1
802.11a 802.11b 802.11g 802.11n 802.11
The 802.11 is the main body of the standard describing the operation of wireless LANs. The standard contains the transmission technology descriptions for Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and infrared. The 802.11 standard describes the operation of DSSS system at 1 Mbps and 2 Mbps data rate transfer. For systems that can operate at other data rates including 1 Mbps and 2 Mbps, the device is 802.11compliant. However, the system must be operating at 1 or 2 Mbps (802.11 compliant mode) to be expected to communicate with other 802.11 compliant devices. IEEE provides one of two standards for the operations of FHSS systems. The IEEE standard describes FHSS systems at 1 and 2 Mbps. The same compatibility issues are in place as with DSSS systems. 802.11 focuses on products that operate within the 2.4 GHz ISM band. The exception is infrared, a light-based technology which is covered by the standard but does not fall into the 2.4 GHz ISM band. 9.2.2
802.11b
802.11b is often referred to as “high-rate” and Wi-Fi. The original standard provided a basic description for operating wireless LANs based on the technology at the time of adoption. Technology grew and eventually outgrew the standard. 802.11b was a successful attempt to update the standard. It's considered high-rate because it describes the operation of DSSS systems at 1, 2, 5.5 and 11 Mbps. By default, 802.11b-compliant Copyright The Art of Service Brisbane, Australia │ Email:
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devices are 802.11-compliant. This allows backward compatibility and allows upgrades to existing networks without replacing core hardware, providing a low-cost solution to remain competitive. The high data rate provided by 802.11b-compliant devices is possible by the use of a different coding technique. The system is still a direct sequencing system, but the chips are coded using CCK rather than Barker Code. The information is modulated differently as well allowing a greater amount of data to be transferred in the same time frame. 802.11b products will only operate in the 2.4 GHz ISM band between 2.4000 and 2.4835 GHz. 9.2.3
802.11a
The 802.11a describes wireless operations in the 5 GHz UNII bands. Operating in the UNII bands make 802.11a devices incompatible with all other devices compliant to other 802.11 series of standards because 5 GHz frequencies do not communicate with systems using 2.4 GHz frequencies. With the UNII bands, devices can achieve data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps. Proprietary technology can raise the data rate as high as 108 Mbps using rate doubling. However, 802.11a specifies data rates of only 6, 12, and 24 Mbps. To be 802.11a-compliant, devices must support these data rates at the very least. The maximum data rate specified by the standard is 54 Mbps. 9.2.4
802.11g
802.11g standard provides data speeds similar to 802.11a but backwards compatible to 802.11 devices. The standard still operates in the 2.4 Ghz ISM band, but utilizes Orthogonal Frequency Division Multiplexing (OFDM) modulation Copyright The Art of Service Brisbane, Australia │ Email:
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which allows higher data rates. Backwards compatibility allows QSPK modulation to communicate with slower 802.11 and 802.11b compliant devices. 9.2.5
802.11n
The primary difference with 802.11n is the inclusion of option modes and configurations. This allows manufacturers to maintain baseline performance parameters while accommodating different customer demands. The options are not required to be supported to be 802.11n compliant. OFDM modulation has been improved to allow an attainable raw data rate of 65 Mbps, up from 54 Mbps in other standards. One of the biggest changes is the adoption of Multiple Input Multiple Output (MIMO), which exploits multipathing by splitting the data stream into multiple parts, called spatial streams, and transmitting each stream from different antennas. 4 spatial streams are supported by the standard. Using 2 spatial streams instead of one essentially doubles the data rate, though power consumption and cost also increases. The technique used to split the data stream is called space-division multiplexing. 802.11n is backwards compatible with 802.11b and 802.11g.
9.3
Major Organizations
In the United States, the FCC provides the laws and regulations for the proper use of wireless networking. The IEEE provides the operational standards used to design and manufacture wireless devices. The results of these two organizations have an impact on the global adoption of wireless standards. However, there are several other organizations that contribute to the growth, education, and adoption of wireless technology in the marketplace. The most recognized of these organizations are: Copyright The Art of Service Brisbane, Australia │ Email:
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9.3.1
Wireless Ethernet Compatibility Alliance (WECA) European Telecommunications Standards Institute (ETSI) Wireless LAN Association (WLANA) Wireless Ethernet Compatibility Alliance
Wireless Ethernet Compatibility Alliance (WECA) promotes and tests for wireless LAN interoperability. The term, Wi-Fi, is often attributed to WECA as it is their mission “to certify interoperability of Wi-Fi products and to promote Wi-Fi as the global wireless LAN standard across all market segments. The term was so powerful, the WECA is now known as the Wi-Fi Alliance. Interoperability requires resolving conflicts from interference, incompatibility, and other problems. When a product meets the requirements described in Wi-Fi Alliance's test matrix, the product is granted a certification of interoperability. This certification can be advertised by the vendors and provides end-users confidence in building a wireless network with devices bearing the Wi-Fi logo. One of the primary checks for interoperability is the use of the 40-bit WEP keys. A 40-bit “secret” key assists in securing the network. The key is actually concatenated with a 24-bit Initialization Vector (IV) to reach 64-bits. Therefore, 40-bit and 64-bit keys are the same thing. In like manner, 104-bit and 128-bit keys are the same; however, WECA does not specify interoperability for 128-bit keys though general practice has shown it exists. Other factors sought after for interoperability for Wi-Fi Alliance include: Fragmentation PSP mode ESSIDs SSID probe requests. 9.3.2
European Telecommunication Standards Institute
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IEEE has for the United States. Often, the standards of the two organizations compete against each other and some discussion has made to unify the standard on certain wireless technologies. IEEE attempted to reach interoperability with 802.11h. The original ETSI standard for wireless networking is called HiperLAN/1. It supported rates up to 24 Mbps using DSSS with a range of 150 feet. The lower and middle UNII bands were used. The HiperLAN/2 standard provides support for rates up to 54 Mbps across all three UNII bands. HiperLAN/2 supports interchangeable convergence layers, including ATM, Ethernet, PPP, FireWire, and 3G. 9.3.3
Wireless LAN Association
The purpose of WLANA is to educate and raise consumer awareness about the use and availability of wireless LANs. It is an educational resource to learn about the concepts of wireless LANs and specific products and services. WLANA also promotes the cooperation of several partners to generate content to the directory of information such as white papers and case studies.
9.4
Competing Technologies
Several technologies compete with the 802.11 family of standards. This is natural as business needs change and technologies improve. Other wireless LAN technologies being used include: HomeRF Bluetooth Infrared OpenAir. 9.4.1
HomeRF
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HomeRF operates within the 2.4 GHz band and utilizes frequency hopping technology. The devices hop approximately 50 hops per second, which is 5-20 times faster than 802.11-compliant FHSS devices. The newest versions of HomeRF take advantage of “wide band” frequencies approved by the FCC, which entail: Maximum of 5 MHz wide carrier frequencies Minimum of 15 hops in a sequence Maximum of 125 mW of output power. The SWAP protocol is used which is a combination of CSMA used in local area networks and TDMA used in cellular phones. SWAP is actually a hybrid of 802.11 and DECT standards. HomeRF is considered to be more secure than 802.11 products using WEP. This is the result of the 32-bit initialization vector (IV) used over 802.11's 24-bit IV. Additionally, HomeRF specifies how the IV is chosen during encryption which is not done by 802.11. 9.4.2
Bluetooth
Bluetooth also operates in the 2.4 GHz ISM band as a frequency hopping technology. The hop rate for Bluetooth is 1600 hops per second. Bluetooth devices are designed for: Low throughput Simple use Low power Short range. One disadvantage of Bluetooth is its persistent interruptions of other 2.4 GHz networks and FHSS systems due to the faster hop rate. The Bluetooth signal appears to other systems as all-band noise or allband interference. Bluetooth operate in three power classes: 1 mW, 2.5 mW and 100 mW. Copyright The Art of Service Brisbane, Australia │ Email:
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9.4.3
Infrared Data Association (IrDA)
IrDA is not a standard, but an organization. Founded in 1993 and funded by members, IrDA's mission is “to create an interoperable, low cost, low power, half duplex, serial data interconnection standard that supports a walk-up point-to-point user model that is adaptable to a wide range of computer devices”. Infrared (IR) is a light-based transmission technology. At close range, the maximum data rate of 4 Mbps is possible, though the typical rate found is 111 kps. Unfortunately, being light-based, other sources of IR can interfere with the transmission. Security for IR devices have two major advantages: IR cannot travel through walls The light beam must be directly intercepted to gain access to the information. A popular use for infrared transmissions is between laptops and handheld devices because of their easy point-to-point connectivity. The maximum range of a point-to-point connection is 1 kilometer, or 3280 feet. 9.4.4
Wireless LAN Interoperability Forum (WLIF)
The WLIF is a defunct organization responsible for the creation of the OpenAir standard. OpenAir was meant to be an alternative to 802.11. Two speeds were specified: 800 kbps and 1.6 Mbps. OpenAir and 802.11 are not compatible. Several products still exist that comply to OpenAir standards.
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10 Infrastructure Devices for Wireless LANs 10.1 Access Points Access points provide an entry point into the wireless network. The hardware is half duplex with an intelligence equivalent to a sophisticated Ethernet switch. Access points have the ability to communicate with the client, the network and other access points. 10.1.1 Modes An access point can be configured in three modes: Root mode Repeater mode Bridge mode. Root mode is typically the default configuration. It is used when connecting the access point to a wired network backbone through a wired interface. Root-based access points are typically Ethernet driven. When multiple access points are connected to the same wired network distribution, they are in communication with each other coordinating roaming functions Bridge mode connects two or more wired networks using wireless access points. Repeater mode provides a wireless upstream link to a wired link. A client will connect to an access point in repeater mode. A wireless connection from the repeater is made with a root access point upstream.
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Use of repeater access points is not recommended because: Cells around each access point must overlap by more than 50%, reducing the range available to clients. Throughput is reduced since the repeater is communicating with the upstream access points and all clients. Users attached to repeaters typically experience low throughput and high latency. 10.1.2 Access Point Options Access points are portals allowing client connectivity from wireless 802.11 networks to wired 812.3 or 802.5 networks. Several hardware and software options are available, including: Fixed or detachable antennas Advanced filtering capabilities Removable (modular) radio cards Variable output power Varied types of wired connectivity. Devices with detachable antennas allow connection to any antenna with any length of cable required. Some access points are shipped with diversity antennas which allow the use of multiple antennas with multiple inputs on a single receiver. An access point may include MAC or protocol filtering capabilities which is used to prevent intruders accessing the wireless LAN. Access points can be configured to filter devices that are not listed in the MAC filter list in the administrative controls of the access point device. Protocol filtering controls what protocols can be used on a wireless link. Some access points have the ability to add special functionality by providing PCMCIA slots. This allows additional radios to be added or removed from the device. With two PCMCIA slots, a device can have one radio card to become an access point while another radio card can act as a bridge or as independent access points increasing the number of users that can connect. Copyright The Art of Service Brisbane, Australia │ Email:
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The administrator can control the power used by the access point to send data through variable power output functions. Controlling powers allow the range of the access point to be controlled. The more power used, the greater the distance available to access the wireless network. Fixed output access points are alternatives. Changes to power can be made using: Amplifiers Attenuators Long cables High-gain antennas. Access points can link to most network types. Understanding the limitations of wired connections to the access point from the core network follows because of network restrictions. 10.1.3 Managing Configurations Configuring and managing access points are dependent on the features set by the manufacturer. Most devices include at least a console, telnet, USB, or built-in web server. Some models may include custom configuration management software. An access point is typically preconfigured with an IP address. A hardware reset button is available to reset the device to factory defaults. Several additional features are available. The more features available, the greater the expense for the device. Some of the features available on Small Office, Home Office (SOHO) devices and Enterprise devices include:
SOHO devices MAC filtering WEP (64-bit or 128-bit) USB or console configuration interfacing Built-in web server configuration interface (simple) Custom configuration applications (simple). Enterprise
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Custom configuration applications (advanced) Built-in web server configuration interface (advanced) Telnet access SNMP management 802.1x/EAP RADIUS client VPN client and server Static or dynamic routing Repeater functions Bridging functions.
Functionality support can vary drastically within the same feature; some devices partially support the feature while others fully support.
10.2 Wireless Bridges A wireless bridge will connect two wired LAN segments. Typical attributes of bridges include: Half-duplex devices Capable of layer 2 wireless connectivity only Used in point-to-point and point-to-multipoint configurations. 10.2.1 Bridge Modes Wireless bridges communicate to other wireless bridges in one of four modes: Root mode Non-root mode Access point mode Repeater mode. In a group of bridges, one bridge will always be configured as the root bridge. A root bridge will never be associated with another root bridge. The communication it has will always be with non-root bridges and client devices. Copyright The Art of Service Brisbane, Australia │ Email:
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Non-root mode allows wireless bridges to attach to other wireless bridges which are not in root mode. Some manufacturers support the ability for clients to connect to non-root bridges while in bridging mode; allowing the device to be an access point and a bridge at the same time. Access point mode provides the bridge access point functionality. In repeater mode, the wireless bridge is placed between two other bridges in order to extend the length of the bridged segment. Unfortunately, use of repeaters typically will reduce the throughput available. 10.2.2 Bridge Options Options available for bridges are the same for wireless access points, including: Fixed or detachable antennas Advanced filtering capabilities Removable (modular) radio cards Variable output power Varied types of wired connectivity.
10.3 Wireless Workgroup Bridges Different from wireless bridges are wireless workgroup bridges, or WGB. WGBs are client devices, allowing multiple wired LAN clients to be aggregated into a single collective wireless LAN client. Workgroup bridges are useful in: Mobile classrooms Mobile offices Remote campus kiosks. With WGBs, the workgroup bridge appears as a single client device in the association table. The MAC addresses of the devices supported by the workgroup bridge are not seen by the access point. A standard bridge can be used, by if an access point is used at the central site, Copyright The Art of Service Brisbane, Australia │ Email:
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an extra bridge device is required. Purchasing a workgroup bridge can alleviate this problem. 10.3.1 Options and Configuration Since wireless workgroup bridges are a type of bridges, they have some of the same options that standard bridges have. Because the WGB supports multiple clients, some thought should be given to how many clients should be supported. Depending on the manufacturer, the range can be from 8 to 128 clients; though more than 30 will cause significant degradation to the throughput.
10.4 Wireless LAN Client Devices A client is any wireless device that uses the access point to enter the network. The devices can include: PCMCIA cards Compact flash cards Ethernet connectors Serial connectors USB adapters PCA adapters ISA adapters. 10.4.1 PCMCIA and Compact Flash Cards PCMCIA cards, or PC cards, are used in notebook computers and PDAs. They provide a connection between the client and the network. The main difference in most PC cards is the antenna. Some antennas are flat and small, while others are detachable and connected using a cable. Compact Flash Cards, or CF cards, are similar to PC cards in Copyright The Art of Service Brisbane, Australia │ Email:
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functionality. They are typically used in PDAs and are the size of a matchbook. 10.4.2 Wireless Ethernet and Serial Converters Converters are for any device having Ethernet or legacy 9-pin serial ports. They convert network connections into wireless LAN connections. Ethernet converters are external devices that connect using the category 5 (Cat5) cable. They have the ability to convert a large number of wired nodes to wireless in a matter of minutes. Serial devices are used on older equipment such as terminals, telemetry equipment and serial printers. 10.4.3 USB Adapters USB Adapters are plug-n-play devices and uses power delivered through the connection from the computer. Some USB clients utilize modular radio cards while others have a fixed internal card. When a PC card is used, it is recommended to use an adapter and card from the same manufacturer. 10.4.4 PCA & ISA Adapters PCI and ISA adapters are installed inside desktop or server equipment. Wireless PCI devices are plug-n-play and may come with an “empty” PCI card which requires the insertion of a separate PCMCIA card to function. Most ISA cards are not plug-n-play and require some configuration through a software utility and the operating system. Typically, the administrator has to change the settings of the adapter to match the settings of the operating system. Drivers for PCI and ISA adapters are usually different and provided Copyright The Art of Service Brisbane, Australia │ Email:
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for by the manufacturer. When a PC card is used, it is recommended to use an adapter and card from the same manufacturer. 10.4.5 Wireless Fixed Adapters The increased demand of wireless capability has caused most computer manufacturers to include a fixed adapter in new equipment, particularly notebook computers and personal devices. 10.4.6 Configuring Adapters Wireless adapters are installed using: drivers manufacturer's wireless utilities Drivers are typically included with the software. Most adapters are plug-and-play, so a prompt for the software is made when the client device is installed. Some devices, such as Ethernet and Serial converters, do not use any special drivers. Utilities provided by manufacturers can range in functionality from simple connectivity to a full suite of utilities, including: Site Survey Tools Spectrum analyzer Power and speed monitoring profile configuration Link status monitor Link testing Site survey tools can be used to: find networks identify MAC address or access points quantify signal strength Copyright The Art of Service Brisbane, Australia │ Email:
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quantify signal-to-noise ratios identify interfering access points
Spectrum analyzer software will find interfering sources and overlapping wireless LAN channels. Power and speed configuration utilities monitor the behavior of the wireless link at any given time. Profile configuration utilities assist in changing from one wireless network to another by creating a profile for each network. Link status monitor utilities allow users to view a variety of components including: Packet errors Successful transmissions Link viability Connection speed Configurable parameters. Though the functionality of the utilities can vary greatly, the configurable parameters are typically the same. They include: Infrastructure mode /Ad Hoc mode SSID Channel WEP Keys Authentication type.
10.5 Wireless Residential Gateways A wireless residential gateway is designed to connect a small number of wireless nodes to a single device. Connectivity to the Internet or another network is capable through the Layer 2 or Layer 3. Most gateways include a built-in hub or switch and an access point which is fully configurable and Wi-Fi compliant. Most residential users are familiar with the WAN port: an Internetfacing Ethernet port that allows connection through: Copyright The Art of Service Brisbane, Australia │ Email:
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Cable modems xDSL modems Analog modems Satellite modems.
Common options found on wireless residential gateways include: Point-to-point protocol over Ethernet (PPPoE) Network address translations (NAT) Port address translation (PAT) Ethernet switching Virtual servers Print services Fail-over routing Virtual private networks (VPN) Dynamic host configuration protocol (DHCP) Configurable firewall. Configuring gateways typically require browsing to a built-in Ethernet ports in order to change the settings for the particular users. Some of the options that are configurable if available are: ISP settings LAN settings VPN settings Console connectivity Telnet connectivity USB connectivity.
10.6 Enterprise Wireless Gateways Enterprise wireless gateways are appropriate for large-scale wireless LAN environments to provide a range of manageable wireless LAN services, such as: Rate limiting Quality of Service(QoS) Profile management. Particularly, the gateway provides specialized authentication and connectivity to wireless clients. Copyright The Art of Service Brisbane, Australia │ Email:
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Enterprise Wireless Gateways differ from residential devices with the existence of more powerful CPUs and faster Ethernet interfaces. This is required to support multiple access points sending traffic to and through the gateway. 10.6.1 Option Support Additionally, most enterprise gateways will support a variety of WLAN and WPAN devices. SNMP is supported and user profiles can be upgraded simultaneously. Other common options include: Hot fail-over RADIUS support LDAP support Windows NT authentication databases Data encryption VPN connectivity 802.1x/EAP connectivity Role-Based Access Control (RBAC) Class of Service support Mobile IP MAC spoofing prevention Complete session logging. 10.6.2 Configuring Enterprise Gateways Enterprise gateways are configured through: Console ports Telnet Internal HTTP or HTTPS servers. Typically, they are installed in the data path of a wired LAN just past the access point. The gateway provides centralized management of multiple devices. Enterprise wireless gateways are upgraded similar to wired switches Copyright The Art of Service Brisbane, Australia │ Email:
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and routers through TFTP. Configuration backups can be automated. Additionally, most gateways are built as rack-mountable 1U and 2U devices to accommodate existing data center designs.
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11 Antennas and Accessories Antennas are a basic component to allow wireless devices to communicate and extend the range of wireless LAN systems. Antennas can enhance the security of the wireless network by reducing signal leaking and preventing signal interception. The right antenna in the right position can provide a proper and secure network environment. Wireless LAN antennas are categorized as: Omni-directional Semi-directional Highly-directional.
11.1 Radio Frequency Antennas Antennas convert high frequency (RF) signals from a cable or waveguide into propagated waves in the air. The electrical fields emitted from an antenna are called beams or lobes. Different categories of antennas offer different RF characteristics. A similar characteristic of all antennas is the effect of controlling gain: namely, as the gain is increased the coverage area narrows. 11.1.1 Omni-Directional Antennas Omni-directional antennas are the most commonly used wireless LAN antenna. Also called Dipole antenna, the omni-directional antenna is standard equipment for most access point. The primary characteristic of a dipole antenna is that the energy emissions radiate in all directions around the antenna's axis. The radiating element of a dipole is one inch long. They support wireless LAN frequencies in the 2.4 Ghz microwave spectrum. One characteristic of an antenna is their size: the smaller they are, the Copyright The Art of Service Brisbane, Australia │ Email:
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higher the frequency supported. An antenna that is capable of radiating in all directions equally, in the shape of a sphere, is called an isotropic radiator. The possibility of this type of antenna is theoretical, the actual radiation of dipole is more closely shaped like a doughnut with the antenna at the center. This is because the dipole will radiate equally in all directions by not along the length of the wire itself As the gain increases, the more horizontal the doughnut is shaped. High gain antennas have a complete horizontal beam with little or no change in the vertical emissions. A number of reasons exist for using omni-directional antennas: Coverage in all directions Large areas of coverage around a central point Point-to-multipoint designs in a hub-n-spoke topology. The positioning of the antenna is important: For outdoors, the antenna should be placed at the top of a structure For indoors, the antenna should be placed near the ceiling at the center of the building. They are most suitable in warehouse or convention type environments. 11.1.2 Semi-Directional Antennas Supported types of semi-directional antennas include: Patch Panel Yagi. These types of antennas can come in different styles and shapes. All are generally flat and can be mounted to the wall. The differences are in the coverage characteristics. Unlike omni-directional antennas, the semi-directional antennae direct the energy in one particular directional, often in a hemispherical Copyright The Art of Service Brisbane, Australia │ Email:
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(Patch) or cylindrical (Yagi) coverage pattern. Semi-directional antennas are typically used for bridging at short or medium ranges. A couple of properly placed semi-directional antennas can provide better coverage than several omni-directional antennas. 11.1.3 Highly-Directional Antennas The signal beam from a highly directional antenna is the narrowest signal beam of any type, as well as the greatest gain. Most highly-directional antennas are dish-shaped devices and are either parabolic dishes or grid antennas. These antennas are ideal for sending signals over distances up to 25 miles. They do not have the coverage usable for client devices, but rather are used for point-to-point communications.
11.2 Concepts of RF Antennas When using RF antennas, several concepts are important to understand. The most important concepts are: Polarization Gain Beamwidth Free space path loss. These concepts are important for determining: The placement of the antenna The positioning of the antenna The power being radiated The distance traveled by the beam The power being received.
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11.2.1 Polarization A radio wave is comprised of two fields: electric and magnetic. Together, they create an electro-magnetic field. Energy is transferred between the two fields in a process called oscillation. The fields are on planes which are perpendicular to each other. The plane that is parallel to the antenna element is referred to as the “Eplane.” The plane perpendicular to the antenna element is referred to as the “H-plane.” Polarization refers to the physical orientation of the antenna. The antenna element is the metal part of the antenna which performs the radiating of the electrical field. The electrical field is always parallel to the radiating element: Horizontal polarization is the electrical field parallel to the ground Vertical polarization is the electrical field perpendicular to the ground. Wireless LANs typically use vertical polarization. Most access points have dual antennas that are vertically polarized. Antennas that are not polarized in the same way are not able to communicate with each other. The topic of polarization explains the reasons why PCMCIA cards do not have adequate coverage since it is difficult to build appropriate antennas into devices that normally sit horizontally. 11.2.2 Gain Gain has the ability to increase the distance that a propagated wave will travel. Antennas that feature passive gain do not increase the power that is inputted, but will change the radiation field to lengthen or shorten the propagated field. 11.2.3 Beamwidth Copyright The Art of Service Brisbane, Australia │ Email:
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Vertical and horizontal considerations are in place when discussing beamwidths. A vertical beamwidth is measured in degrees and perpendicular to the surface of the Earth. A horizontal beamwidth is also measured in degrees and parallel to the surface of the Earth. For different antenna types, here are the documented specifications: Antenna type
Horizontal Beamwidth
Vertical Beamwidth
Omnidirectional
360
Ranges from 7-80
Patch/Panel
Ranges from 30180
Ranges from 6-90
Yagi
Ranges from 3078
Ranges from 1464
Parabolic Dish
Ranges from 4-25 Ranges from 4-21
11.2.4 Free Space Path Loss Sometimes simply referred to as Path Loss, Free Space Path Loss is the measurable loss incurred by an RF signal due to “signal dispersion.” Signal dispersion is the natural broadening of the wave front. The wider the front is, the less power which is induced into the receiving antenna. Power is important factor in link viability. When a signal travels through the atmosphere, its power decreases at a rate inversely proportional to the distance traveled and proportional to the wavelength of the signal. Path Loss is the single greatest source of loss in a wireless system and one of the foundations of calculating link budgets using the formula: Path Loss = 2LOG10[4Πd/λ]{dB} Copyright The Art of Service Brisbane, Australia │ Email:
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The equation above identifies a relationship between the loss in decibels and the distance traveled by the signal. As the distance doubles, an increase of 6dB in the EIRP occurs. Below is a sample of calculations: Distance
Loss
100 meters
80.23
200 meters
86.25
500 meters
94.21
1,000 meters 100.23 2,000 meters 106.25 5,000 meters 114.21 10,000 meters
120.23
11.3 Antenna Installation Installation of antennas is one of the most important considerations after determining the type of antenna. The factors associated with installing antennas include: Placement Mounting Proper use Orientation Alignment Safety Maintenance. 11.3.1 Placement Omni-directional antennas should be located as close to center of the desired coverage area as possible. The antenna should be placed as high as possible while considering that the high-gain antennas have a narrower vertical axis to the transmission field. Copyright The Art of Service Brisbane, Australia │ Email:
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Outside antennas should be mounted above obstructions such as tree and buildings that could encroach on the Fresnel Zone. Planning for future development of growth should be considered, i.e. trees that currently do not block the antenna may grow to significantly block the signal in 10-20 years. 11.3.2 Mounting Several options are available to mount antenna: Ceiling mount – hung from crossbars of drop ceilings Wall mount – forces the signal away from a perpendicular surface Pillar mount – mounts flush to a perpendicular surface Ground plane – sits flat on the ground Mast mount – mounted to a pole Articulating mount – mast mount that can be moved Chimney mount – mounted to structure's chimney Tripod-mast – mounted to a tripod. 11.3.3 Proper Use The most important factor in proper use of antennas is whether it is designed for inside or outside use. Outside antennas are designed with seals and plastics to protect the element from water, heat, and cold. Inside antennas are not. 11.3.4 Orientation The orientation of the antenna determines polarization. Two antennas must have the same orientation in order to communicate between each other. Therefore, if the access point is parallel to the Earth's surface, the antennas on the clients must also be parallel. The same is true for antennas perpendicular to the surface. 11.3.5 Alignment Copyright The Art of Service Brisbane, Australia │ Email:
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Alignment becomes increasingly important the more highly directional the antenna. Some antennae have very wide beamwidths so that two antennas can be aimed in the general direction of each other. Wireless bridges come with alignment software to optimize antenna reception. The concerns using omni-directional or semi-directional are usually focused on getting the greatest coverage of the appropriate area. 11.3.6 Safety RF antennas are electrical devices and as such can be dangerous to implement and operate. Some basic guidelines include: Use professional installers, especially for elevated installations If not using professional, follow the manual High-gain antennas utilize high levels of power: touching or directing an antenna while it is transmitting is very dangerous Antennas should be installed away from any metal obstructions to reduce the amount of multipathing as well as reflection of dangerous levels of high power Recommendations related to power lines is keep antennas at least 2 times the height of the antennas from all overhead power lines Grounding must be appropriate and follow the National Electric Code and local electrical codes. 11.3.7 Maintenance Outdoor antennas require the greatest amount of maintenance because of their exposure to heat, cold, and other weather conditions. Water is the biggest problem to antennas requiring sufficient sealing of connectors.
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11.4 Power over Ethernet (PoE) Devices When AC power receptacles are not available to power a unit, wireless devices can receive DC power over a Cat5 Ethernet cable. The method is called Power of Ethernet (PoE). The cable used will carry both power and data to the unit. This is done with a POE device on the cable line. Cable requirements related to data transfer still apply, namely that Ethernet cables can only carry data reliably for 100 meters. PoE has such great advantages that some manufacturers build devices that will only use PoE. 11.4.1 PoE Options Several types of PoE devices exist, including: Single-port DC voltage injectors Multi-port Voltage injectors Ethernet switches designed to inject DC voltage. Configuration and management is not necessary for a PoE device, though some considerations must be taken into account. No industry standard exists for the implementation of PoE to describe how PoE equipment interfaces with other devices, therefore, if you are using a PoE device to power an access point, it is best to use devices from the same manufacturer. The output voltage required to power a wireless LAN will be different form one manufacturer to the next. Using devices from the same manufacturer will mitigate any compatibility issues. The current that is carried over Ethernet utilizes unused pins that are not standardized. One manufacturer may use pins 7 and 8 while another uses 4 and 5. If a wireless LAN device does not accept power on those pins, the device will not power up. Single-port DC voltage injectors are used to power wireless LAN devices. They are specifically used when the use of PoE is Copyright The Art of Service Brisbane, Australia │ Email:
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mandatory for the access point or bridge. Single-port injectors should only be used in small networks to prevent clutter. For medium-sized networks, a multi-port injector will support the power requirements for several devices, typically manufactured to have 4, 6, or 12 output ports. The PoE device is typically sitting within a wiring closet and connected to a switch or hub on the input port and the wireless devices on the output ports. Up to 50 access points can be supported. Large sized networks would benefit from the installation of active Ethernet switches. The device incorporates DC voltage injections into the Ethernet switch. The benefit is the support of large numbers of PoE devices without additional hardware. In most cases, an active Ethernet switch can auto-detect any PoE requirements on the network. If PoE is not required, than the DC voltage is switched off on the connecting port. 11.4.2 Compatibility for PoE Devices that are not designed to use PoE can be converted using a DC “picker” or “tap.” Also called active Ethernet “splitters,” these devices siphon the DC voltage that was injected in the Cat5 cable by the injector and makes it available to the non-PoE device through a regular DC power jack. Using Power-over-Ethernet requires the use of an injector. If the wireless device is PoE compatible, no other equipment is required. If the device is not PoE compatible, a picker is required. 11.4.3 Injector Types Injectors come in two types: Passive Fault protected. A passive injector simply places a DC voltage onto a Cat5 cable. Copyright The Art of Service Brisbane, Australia │ Email:
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A fault protected injector also places a DC voltage on a Cat5 cable, but also provides continuous fault monitoring and protection to detect short circuits and over-current conditions. 11.4.4 Picker Types Pickers come in two types: Passive Regulated. A passive picker will take the voltage from the Cat5 cable and direct it to the equipment. Therefore, the equipment will receive whatever VDS (Volts of Direct Current) were originally injected. A regulated tap will take the voltage from the Cat5 cable and convert it to another voltage, typically standard regulated voltages of 5 VDC, 6 VDC, and 12 VDC. 11.4.5 Standards for Voltage and Pinouts The injected PoE voltage has been standardized at 48 VDC by the IEEE. However higher voltage will reduce the current flowing through the Cat5 cable. This will cause the load to increase and the limitations on the length of the Cat5 cable. Some manufacturers have decided to utilize 12 or 24 VDC. 11.4.6 Fault Protection Fault protection is meant to protect the cable, equipment and power supply from short-circuit or fault. Under normal operations, faults are highly unexpected; though several causes may contribute: Incompatibility with PoE Non-standard or defective connectors Incorrectly wired Cat5 cabling Cut or crushed Cat5 cabling. Copyright The Art of Service Brisbane, Australia │ Email:
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Fault protection will shut DC voltage off whenever a fault condition exists. Circuit operation varies from one model to the next. Restoring power is dependent on the device model. Some models will continuously monitor the cable and automatically restore power when the fault has been resolved. Other models must be manually reset.
11.5 Accessories for Wireless LAN Several accessories can be added to a wireless network to: Maximize throughput Minimize signal loss Ensure proper connections. Types of accessories possible are: RF Amplifiers RF Attenuators Lightning Arrestors RF Connectors RF Cables RF Splitters. 11.5.1 RF Amplifiers Devices designed to “amplify;” to increase the amplitude of the RF signal. The measure of an amplified signal is noted as +dB. Typically amplifiers are used to compensate for the expected loss of the signal due to distance. Most amplifiers are powered using DC voltage and located near the access point or bridge. The DC voltage is sometimes called phantom voltage because the RF amplifier seems to power up without cause. Two types of amplifiers exist: Unidirectional Bi-directional. Copyright The Art of Service Brisbane, Australia │ Email:
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Unidirectional amplifiers will compensate for signal loss by increasing the signal level before being injected into the transmitting antenna. Bi-directional amplifiers will amplify the received signal before it is fed into the access point, bridge, or client device. Each type of amplifier can have one of two additional options: Fixed gain Variable gain. Fixed gain amplifiers apply a fixed amount of gain to the RF signal, while variable gain provides a manual means of configuring the desired amount of gain required from the equipment. To determine the right amplifier, certain specifications should be taken into consideration, including: Frequency response (range in Ghz) Impedance (ohms) Gain (dB) VSWR Input (mW or dBm) Output (mW or dBm). Frequency response is a big determiner for selecting the right amplifier. If a wireless LAN uses a 5 Ghz frequency spectrum, an amplifier that works within the 2.4 Ghz spectrum will not work. The impedance of the amplifier should be the same as all the other wireless LAN hardware between the transmitter and the antenna, though typically they will be about 50 ohms. Since the amplifier will be connected to the network, consideration must be made around the kinds of connectors used. Most amplifiers use either SMA or N-type connectors. Amplifiers are generally mounted to a solid surface. Unless the amplifier allows variable gains, there are no configurations required. Variable amplifiers have to be adjusted to the proper amount of amplification. Copyright The Art of Service Brisbane, Australia │ Email:
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11.5.2 RF Attenuators A device that causes precise measured loss in an RF signal. The common reason for decreasing the RF signal is to meet FCC rules when the equipment available for the network will provide a much greater signal strength than allowed by the regulation. Like amplifiers, attenuators can be either fixed or variable. The same considers for selecting amplifiers and attenuators are the same. Fixed attenuators typically have BNC or SMA connectors. The placement of an attenuator is directly between the transmitter and the antenna. Configuration is not required unless the attenuator allows variable loss. 11.5.3 Lightning Arrestors These devices provide protection to access points, bridges, and workgroup bridges attached to coaxial transmission lines. Coaxial transmission lines are susceptible to lightning strikes. A lightning arrestor will redirect the transient current caused by lightning into the ground. Generally, the lightning arrestor will redirect up to 5000 amperes at up to 50 volts. When lightning strikes a nearby object, transient currents from the strike are induced into the antenna or transmission line. The lightning arrestor senses these currents and ionizes the gases to cause a short directly to the earth ground. The cost of a lightning arrestor is between $50 and $150. When purchasing an arrestor, some considerations include: Must meet IEEE standard of <8 μS Reusable Gas tube breakdown structure Connector types Frequency response Impedance Insertion loss Copyright The Art of Service Brisbane, Australia │ Email:
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VSWR rating Warranty.
IEEE specifications state that arrestors be able to trigger a short to the ground in under eight microseconds (μS). Most lightning arrestors do this in two. Arrestors utilize a gas discharge tube to facilitate a short. If the tube cannot be replaced, the lightning arrestor is only good for one lightning strike. The best option is to choose an arrestor where the tubes can be replaced, since tubes are cheaper than the entire arrestor. Suggestions for placing lightning arrestors indicate they should be the last component on the RF transmission line before the antenna. This is to protect any amplifiers or attenuators on the line. Some arrestors allow DC voltage to be passed through to power RF amplifiers. This is important if the design requires amplifiers to be closer to the antenna than the arrestor. In these cases, the gas tube breakdown voltage should be higher than the voltage required to power the RF amplifier. Connector types used with the arrestor should match the same connectors used with the wiring used, to prevent signal loss due to adapter connectors. The frequency response specification for an arrestor should be as high as the highest frequency used on the wireless LAN. Impedance should match on all devices on the network. The insertion loss should be significantly low to prevent amplitude loss as the signal passes through the arrestor. The good quality lightning arrestor will have a VSWR rating of 1.1:1, though 1.5:1 can still provide sufficient support. The lower the ratio of the device, the better. Malfunctions are still possible no matter the quality of the equipment, so a good warranty should be obtained. Copyright The Art of Service Brisbane, Australia │ Email:
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Lightning arrestors require no configuration. The grounding connection should be attached to the ground with a measurable resistance of 5 ohms or less. 11.5.4 RF Splitters An RF splitter will split a single signal into multiple independent signals. The device has a single input connector with multiple output connectors. The use of a RF splitter is not recommended. The use of a splitter is advantageous when setting up two like panel antennas in opposite directions to create a bi-directional coverage area. However, in this case, it is best to ensure the splitter is midpoint between the two antennas with equal length of cable. The input connector should always face the source of the RF signal. The output connectors, or taps, should face the destination of the RF signal. Splitters are also used to track power output. By connecting a power meter to one output connector and the antenna to the other, the power output can be actively monitored at any given time. The power meter, the antenna, and the splitter must have the same impedance. When choosing an RF splitter, the following considerations should be taken: Insertion loss Frequency response Impedance High isolation impedance VSWR rating Power ratings Connector types Calibration report Mounting DC voltage passing. Copyright The Art of Service Brisbane, Australia │ Email:
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The insertion of an item into the circuit can cause a loss of signal. A splitter should have a low insertion loss to prevent any significant decrease in the RF signal. An insertion loss of 0.5 dB or less is acceptable for an RF splitter. The specification for frequency response for a slitter should be as high as the highest frequency used in the wireless LAN. The impedance for the splitter should be the same as all other devices on the circuit, typically 50 ohms. High isolation impedance should exist between ports on a RF splitter for several reasons: The load on one output port should not affect the output power of another output port A signal arriving into the output port should go to an input port rather than an output port. Isolation speaks to signal separation caused by resistance. Typically, isolation is 20 dB or more between ports. Reverse port isolation is a function of a splitter that allows administrators to convert outputs into inputs. This assists in connecting 2 or more access points or bridges to a single RF antenna. Splitters are rated for the maximum power input, or the most amount of power that can be fed through the splitter without damaging it. N-type and SMA connectors are the most common for splitters. All RF splitters should have a calibration report which shows information about insertion loss, frequency response, etc. It is recommended to calibrate splitters to identify and resolve any degraded performance. Calibration does require taking the wireless LAN off line for an extended period of time. Mounting of a splitter typically requires screwing the equipment through flange planks. Some models come with U bolts for pole mounting. A splitter may or may not be weatherproof which may Copyright The Art of Service Brisbane, Australia │ Email:
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impact any requirement for outside mounting. Some RF splitters will allow DC voltage to pass to all output ports in parallel. 11.5.5 RF Connectors Several connector types, or derivatives, are used to connect devices to cables, including: N-type F-Type SMA BNC TNC. The FCC and DOC (Canadian Department of Communications) ruled in 1994 that connectors for use with wireless LAN devices should be proprietary between manufacturers resulting in several variations of each connector type. Five considerations should be taken when purchasing and installing an RF connector: The connector should match the impedance of all other wireless LAN components, typically 50 ohms. Identify the insertion loss for each connector in the signal path. Identify the upper frequency limit, or frequency response, for the particular connectors used. The higher the limit, the better. Ensure connectors are of good quality and should be purchased from a reputable company and by name-brand manufacturers. Ensure the type and sex (male or female) of the connector. 11.5.6 RF Cables Sometimes referred to as “LMR cable” since this type of cable has Copyright The Art of Service Brisbane, Australia │ Email:
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become a standard for the industry. The criteria for choosing the proper RF cable consists of: Frequency response is the most important consideration: 2.5 Ghz wireless LANS must use a cable rated for at least 2.5 Ghz, for 5 Ghz LANs, a cable rating of at least 6 Ghz. Cables introduce loss into wireless LANs, and can be resolved using the shortest cable length possible. Purchasing of pre-cut lengths of cables with pre-installed connectors reduces the chance of bad connections between the connector and the cable. Cable should have the same impedance as all other wireless LAN components on the circuit. The lower the signal loss attributed to the cable, the more expensive the cable. Adding cables also introduce loss. 11.5.7 RF “Pigtail” Adapter Cables Pigtail adapter cables are used to connect cables with industry standard connectors to manufacturer's proprietary connectors. In essence, the adapter cables convert the connectors to N-type and SMA industry standard connectors.
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12 802.11 Network Architecture Wireless LANs provide unique challenges to network administration and architecture design.
12.1 Identifying Wireless LANs When a wireless LAN client is initially installed, configured, and powered, the first action it will take is to scan, or “listen,” for any wireless networks within range. Scanning is performed before any other action in order to find the network. Two types of scanning are possible: Passive scanning Active scanning. When scanning for a network, the client is in search of an access point. The search is aided by a series of “clues” left by the access point in the form of service set identifiers (SSID) and beacons. 12.1.1 Service Set Identifier A SSID is a unique, case sensitive, alphanumeric value of 2-32 characters used as a network name by wireless LANs. The purpose of a network name serves to: Segment the network Secure the network Process of joining a network. The SSID value is sent in beacons, probe requests, probe responses and other types of frames. A wireless client has to be configured for the correct SSID in order to join a network. Each access point is configured with a SSID, which is sometimes referred to as the ESSID. This is usually performed manually by an administrator, though some stations have the ability to use any SSID value. Copyright The Art of Service Brisbane, Australia │ Email:
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In order for a client to work and roam seamlessly, the client and access point must be configured with matching SSIDs. 12.1.2 Beacons Beacon management frames, or beacons for short, are short frames sent from the access point to stations or station-to-station to organize and synchronize wireless communications. Several functions are fulfilled by beacons, including: Time Synchronization FH or DS Parameter Sets SSID Information Traffic Indication Map (TIM) Supported Rates. Clients are synchronized using a timestamp given at the exact time of transmission. When a client receives the beacon, it will change its clock to match the clock of the access point. Time synchronization is essential to ensure that time-sensitive functions, such as frequency hopping, is performed correctly. Within the beacon is a beacon interval which communications how often the client can expect another beacon. A beacon contains information to support the spread spectrum technology: Hop and dwell parameters and hop sequences for FHSS systems Channel information for DSSS systems. Beacons contain the SSID of the network. Stations look to the beacon for that SSID. When found, the station looks at the MAC address where the beacon originated and sends an authentication request to communicate with the access point. If a station can accept any SSID, it will attempt to join the first access point it finds or the access point with the strongest signal. Copyright The Art of Service Brisbane, Australia │ Email:
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The TIM acts as an indicator of sleeping stations which have queued packets at the access point. The information is shared to all associated stations by each beacon. Synchronized stations will power up their receivers, listen for the beacon, and check the TIM for listing. If the station is not listed, the receiver is powered down and it continues sleeping. The standard used by the hardware will determine the speeds supported by the wireless network. The supported speeds are communicated to the stations through the beacon. 12.1.3 Passive Scanning Passing scanning is the process of listening for beacons on each channel for a specific period of time after initialization. The beacons can be sent by either access points or clients and the scanning station will catalog relevant characteristics of each sending station based on the beacons. This continues until the SSID of the network it wants to join is identified. In a network with multiple access points, the SSID may be broadcasted by more than one access point. In these cases, the station will attempt to join using the access point with the strongest signal strength and the lowest bit error code (BER). BER is the ratio of corrupted packets to good packets which is determined by the Signal-to-Noise Ratio of the signal. Passive scanning continues after the station is associated with an access point. This encourages a viable connection with the network as it saves time reconnecting in the event that the client is disconnected. The reconnection is enabled because the passive scan logged a list of available access points and their characteristics, such as: Channel Signal strength SSID. With this information, the station can quickly identify the best access Copyright The Art of Service Brisbane, Australia │ Email:
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point to use. This also aids in roaming stations. Roaming happens as the station moves from one access point to another typically because the station itself is in motion which is possible for mobile computing. The trigger for finding a new access point is the decrease of the signal strength to a specified low level. To architect wireless network solutions to support roaming, the specified overlap between access points is 20-30%. This overlap allows seamless disconnection and reconnection without the user's knowledge. 12.1.4 Active Scanning Active scanning will send a probe request frame from a wireless station when they are actively seeking a network to join. The probe request will either contain the SSID of the network they wish to connect to or a broadcast SSID. If the probe request has a specific SSID, only access points supporting that SSID will response with a probe response frame. If a broadcast SSID is sent, all access points will respond. The purpose of probing in this manner is to locate specific access points from which to attach to a network. The information provided by the probe response frames is almost identical to the information found in beacons. The difference is the exclusion of the timestamp and the TIM. The signal strength of the probe response frame will assist in determining the access point the station will attempt to associate. The chosen access point is typically based on a strong signal strength and low BER.
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12.2 Authentication and Association Connecting to a wireless LAN consists of two separate subprocesses: Authentication Association. Authentication speaks the acceptance of the radio PC card, not the user. Association refers to connectivity at Layer 2. 12.2.1 Authentication Connecting to a wireless LAN starts with authentication, a process where a wireless node, such as a PC card, USB Client, or adapter, has its identify verified by the network. Sometimes the authentication process is null which allows a client and access point to associate without any special identity required. This is often the case when new access points or clients are installed in default configurations. Authentication starts when the client sends an authentication request frame to the access point. The access point will accept or deny the request and notify the client of the decision through an authentication response frame. Sometimes this decision is made by the access point, or it may be configured to pass the request along to an upstream authentication server, such as RADIUS. 12.2.2 Association Once a wireless client has been authenticated, the association process starts. To be associated means the client is allowed to pass data through an access point. This ensures that the client communicate with the network through the access point. When a client wants to connect, the authentication request is sent Copyright The Art of Service Brisbane, Australia │ Email:
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and an authentication response is received. At this point, an association request frame is sent to the access point. An association response frame is sent back confirming the association or not. 12.2.3 States of Authentication and Association The complete process of authentication and association has three distinct states: Unauthenticated and unassociated Authenticated and unassociated Authenticated and associated. When a wireless node is completely disconnected from the network and unable to pass frames through an access point, the client is considered to be in a state of being unauthenticated and unassociated. Different vendors refer to this state differently in their access points' association table, which tracks whether a client has completed the authentication process or attempted and failed. The typically notation in the table is “unauthentication.” When the wireless client has passed the authentication process but has still not associated with the access point, they are in the state of authenticated and unassociated. The association table typically notes this state as “authenticated.” The processes of authentication and association happen very quickly, in just milliseconds. When the wireless client is completely connected to the network and sending and receiving data through the access point, it is considered to be in the state of being authenticated and associated and its notation in the association table is “associated.” Given these three states, it is best that most advance security steps are performed when the client is attempting to authenticate.
12.3 Authentication Methods Two methods of authentication are specified by IEEE 802.11 standards: Copyright The Art of Service Brisbane, Australia │ Email:
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Open System authentication Shared Key authentication.
12.3.1 Open System Authentication Open System authentication is the simplest and most secure of the two methods. The IEEE 802.11 specifies this as the default setting for wireless LAN equipment. The method is one of null authentication. Authentication is given based on the possession of the right SSID. The process is effective in both secure and non-secure environments. The process of Open System Authentication follows: A request is made by the client to associate with the access point. The access point authenticates the client and sends a positive response. Though there are several reasons for using Open System authentication, the two primary reasons are: It is the most secure of the two methods It requires no configuration at all since it is the default setting for all 802.11 devices. A wireless LAN administrator has the option of using WEP encryption with Open System authentication. If this option is taken, no verification of the WEP key happens until the client is authenticated and associated. 12.3.2 Shared Key Authentication The use of WEP is required for Shared Key authentication. The WEP key is typically manually entered by the administrator on both the client and the access point. The process of Shared Key Authentication follows: A request is made to associate with an access point by the client. Copyright The Art of Service Brisbane, Australia │ Email:
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The access points issues a challenge to the client, which is a randomly generated plain text. The client responds to the challenge by encrypting the change text with the WEP key set on the client and sending it back. The access point decrypts the response to ensure the encryption matches the WEP key. If the WEP keys match, authentication completes by sending the client a positive response. If a match is not made, a negative response is not made.
Shared Key authentication is not considered secure because the access point transmits the challenge text in the clear and receives the same challenge text encrypted. This allows a hacker using a sniffer to see both the plaintext challenge and the encrypted challenge and create a simple cracking program to derive the WEP key. The WEP key is commonly confused with “shared secret.” A shared secret is a string of numbers or text that provide an alternative test to authenticate. Authentication documents, or certificates, are another form of authentication. Both methods have traditionally been manually configured, but applications have started to work automatically.
12.4 Emerging Authentication Protocols Several authentication solutions and protocols are on the market, including VPN and 802.1x using EAP. Most solutions resort to passing authentication requests through the access points to upstream authentication servers. 12.4.1 802.1x and EAP Windows has native support for 802.11, 802.1x, and Extensible Authentication Protocol (EAP), as does Cisco and other wireless LAN manufacturers. 802.1x is a port-based network access control standard. Devices Copyright The Art of Service Brisbane, Australia │ Email:
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using this standard have the ability to allow a connection into the network at layer 2 only when user authentication is successful. This is beneficial to keep users disconnected when they are not supposed to be on the network. EAP is a layer 2 protocol that allows plug-ins at either end of a link from which several methods of authentication can be used. It is a flexible replacement for PAP and CHAP under PPP which are used for user authentication on wired LANs and support using passwords. EAP provides the same functionality on wireless LANs. User authentication is usually accomplished using a Remote Authentication Dial-In User Service (RADIUS) server and some type of database such as: Native RADIUS NDS Active Directory LDAP. In the 802.1x standard model, network authentication consists of three pieces, the supplicant (client), the authenticator (access point), and the authentication server. The process for 802.11x and EAP follows: The client makes a request to associate with an access point. The access point requests the EAP identity of the client. The client responses to the access point's request who forwards the response to the Authentication Server. The Authentication Server makes a request for EAP authentication to the access point who forwards to the client. The client responds to the request back to the access point who forwards to the Authentication Server. The Authentication Server verifies the association to the access point and further to the client. There are several types of EAP authentication that are used to secure a wireless LAN connection. Understanding the EAP type assists in understanding the authentication methods used like: Copyright The Art of Service Brisbane, Australia │ Email:
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Passwords Key generation Mutual authentication Protocol.
Some of the commonly deployed EAP authentication types include: EAP-MD-5 Challenge – the earliest EAP authentication type duplicating the CHAP password protection on wireless networks. EAP-Cisco Wireless – also called Lightweight Extensible Authentication Protocol (LEAP), this type is primarily used in Cisco wireless LAN access points to provide security during credential exchange, encrypt data transmission using dynamically generated WEP keys, and support mutual authentication. EAP-TLS (Transport Layer Security) – provides certification-based, mutual authentication of the client and the network. EAP-TTLS – an extension of EAP-TLS requiring only server side certificates and can support legacy password protocols. EAP-SRP (Secure Remote Password) – a secure, password-based authentication and key exchange protocol used to securely authenticate clients to servers where the user must memorize a small secret, such as a password without any other information available. EAP-SIM (GSM) – used as a mechanism for Mobile IP network access authentication and registration key generation using the GSM Subscriber Identity Module (SIM). 12.4.2 VPN Solutions VPN secures transmitted data between two network devices over a medium which has an unsecure data transport. The most common use of VPN is to link remote computers and networks to a corporate server through the Internet. The process used by VPN creates a tunnel on top of a protocol like IP Copyright The Art of Service Brisbane, Australia │ Email:
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to allow encrypted traffic through the tunnel totally isolated. Three levels of security exist with VPN: User authentication ensures that only authorized users can connect, send, and receive data Encryption provides additional protection to ensure that transmissions are difficult to decode if ever intercepted Data authentication provides data integrity on the network, ensuring that all traffic is from authentication devices only. Applying VPN technology to a wireless network must be approached differently than applying to a wired network. The reasons for this are: The repeater function of wireless access points that automatically forwards information between wireless LAN stations on the same wireless network. The range of the network will extend beyond the physical limits of an office or home, giving additional opportunity to compromise the network.
12.5 Service Sets Service sets describe the basic components of a fully operational wireless LAN. There are three options for configuring a wireless LAN and different hardware is required for each configuration: Basic service set Extended service set Independent basic service set. 12.5.1 Basic Service Set (BSS) A basic service set consists of only one access client and one or more wireless client. A BSS utilize infrastructure mode requiring the use of an access point and that all traffic transverses that access point. Communication from one wireless client to another must go through Copyright The Art of Service Brisbane, Australia │ Email:
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the access point. A single cell, or RF area, is covered by the access point. The cell consists of varying data rate zones that can be imagined as concentric circles of differing data speeds. The actual data speeds are dependent on the technologies used, for instance, 802.11b equipment would provide data speeds of 11, 5.5, 2 and 1 Mbps. The data rates decrease the farther they are from the center. A BSS has one unique SSID. 12.5.2 Extended Service Set (ESS) An extended Service Set is comprised of two or more basic service sets. The sets are connected by a common distribution system. Distribution systems can be any method of network connectivity. To operate in infrastructure mode, an ESS must have at least two access points. All transmissions must travel through one of the access points. Some additional characteristics of ESS from the 802.11 standard include: Covers multiple cells Allows but does not require roaming Does not require the same SSID for all BSS. 12.5.3 Independent Basic Service Set (IBSS) An IBSS is known as an ad hoc network. No access point or other access to a distribution system exists. The IBSS covers a single cell and has one SSID. The clients share the responsibility of sending beacons to each other. In order to transmit outside of the IBSS, one client must also act as a gateway or router. A software solution can serve this purpose. Copyright The Art of Service Brisbane, Australia │ Email:
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Because clients make direct connections with each other to transmit data, the solution is often referred to as a peer-to-peer network.
12.6 Roaming A wireless client has the ability to move seamlessly from one cell to another without losing network connectivity. This is referred to as roaming. Essentially, one access point will hand the client over to another access point without the knowledge of the client. Ideally in an environment with multiple access points, the coverage area for each access point will overlap. Overlapping coverage is a critical aspect of wireless LAN setup, because it allows error-free roaming. When two or more access points overlap, the client will establish the best possible connection with one of the access points while continuously searching for the best access points. The function is similar to the handover used by cellular phones with two differences: The transition from one cell to the next occurs between packet transmissions on a LAN system, while it occurs during the conversation for a telephony solution. For voice communications, a temporary disconnection may not affect the conversation, while in a packet transmission, performance can be significantly reduced. 12.6.1 Standards Though 802.11 does not define how roaming should be performed, it does provides the basic building blocks. These blocks include: Passive scanning Active scanning Reassociation process. The reassociation process refers to the event of a client reassociating itself with another access point when it is roaming along the network. Copyright The Art of Service Brisbane, Australia │ Email:
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The 802.11 standard allows a client to roam across access points which are on the same of different channels. Clients use the beacon from access points to gauge the strength of their existing connection. The 802.11b standard addresses the news of mobile radio communications to tolerate the dropping and re-establishment of connections to minimize the disruption to data delivery. 12.6.2 Connectivity How the client associates with an access point is guided by the 802.11 MAC layer. The signal strength and observed packet error rates are the criteria for the client to choose an access point. Even after the client has associated itself with an access point, it will survey all 802.11 channels to assess whether a different access point will provide a better connection. A manufacturer-defined signal strength threshold identifies when a client must attempt to find another access point. 12.6.3 Reassociation When a wireless client physically moves farther from the original access point weakening the signal, the client must reassociate with the network. Reassociation also occurs when the characteristics of the radio signal changes or the original access point slows down due high traffic. Load balancing is a form of reassociation which distributes the total wireless LAN load across the wireless infrastructure. Association and reassociation is slight different in how they are used. Association request frames are used when joining a network for the first time. Reassociation request frames are used during roaming between access points. Dynamic association and reassociation with access points is an Copyright The Art of Service Brisbane, Australia │ Email:
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opportunity for network management to set up wireless LANs with broad coverage using a series of overlapping 802.11 cells throughout the network. Success means employing channel reuse; that is, ensuring that 802.11 DSSS channels do not overlap with a channel used by a neighboring access point. 12.6.4 VPN There are two ways for implementing wireless VPN solutions: A centralized VPN server implemented upstream from the access points A distributed set of VPN servers. The first method has the VPN server between the wireless user and the core network. This provides a level if security similar to wired VPNs. The VPN server can also act as a gateway and firewall of added security. The second method can provide security for small and medium sized organizations without any requirement for an external authentication mechanism. Tunnels are built from the client to the VPN server. When a client roams, it does so across Layer 2. This process is seamless to Layer 3 connectivity. However sometimes, a Layer 3 boundary is crossed. This requires a mechanism to keep the tunnel in place. 12.6.5 Layer 2 and 3 Boundaries Wired networks are often segmented in order to manage them better. This allows an effective method of containing broadcast transmissions and to control access between segments. The segmentation is done on Layer 3, but can be done on Layer 2 using VLANs on switches and routers. When using wireless devices, users must have a way to roam across router boundaries without losing their layer 3 connection. This is often done by using subnet-roaming capabilities or by connecting all Copyright The Art of Service Brisbane, Australia │ Email:
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access points to a single subnet. Many environments cannot embrace a single subnet solution. As a result, access points cannot cross boundaries. A hardware solution to the problem is to deploy all access points on a single VLAN using a flat IP subnet. This allows clients to connect and roam through the network without changing the IP address. 12.6.6 Load Balancing Congested areas may require multi-cell structures which have several co-located access points covering the same area in order to increase the aggregate throughput. In this situation, a client will attempt to associate with an access point that is less loaded and provides the best signal quality. Under normal operations, the clients are equally divided between the available access points. This allows efficiency to be maximized.
12.7 Power Management Features 802.11 standards specify two power management modes for wireless clients. They are: Active mode, or continuous aware mode (CAM) Power mode, or power save polling (PSP). 12.7.1 Continuous Aware Mode The setting used when the wireless client uses full power and is in full communication with the access point. There is no need to conserve power as the device is plugged into an AC power outlet. 12.7.2 Power Save Polling PSP mode allows wireless client to “sleep”. Sleep involves powering down the device for a short time with the purpose of saving a Copyright The Art of Service Brisbane, Australia │ Email:
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significant amount of power. This allows the client, namely mobile devices, to work for a longer period of time when on battery power. PSP mode in a BSS has clients sending frames to the access point to provide notice that they are going to sleep. The access point will buffer any frames intended for the sleeping client. The queued packets will be delivered when the client awakens. The access point constantly sends out beacons. Clients know when to receive the beacons. Clients that are sleeping are still listening for beacons to read the TIM. If the TIM lists the client, it powers up and sends a frame to the access point identifying that it is awake. In IBSS, no access point exists, so there is no device to buffer packets. As a result, all the clients in the network will be responsible to buffer packets intended for other clients on the network. Ad hoc traffic indication messages (ATIM) windows are a period of time when the wireless devices are fully awake and ready to receive data frames. TIMs are unicast frames used to notify the network clients that data is being buffered for them and that they should awaken for as long as required to receive the data. The process is: Clients are synchronized by the beacons which will wake them before the ATIM window begins When it does begin, the clients send beacons and ATIM frames to notify other clients of buffered traffic Clients receive ATIM frames when they are awake. If there are no ATIM frames, the clients go back to sleep The ATIM windows closes and clients begin transmitting. After receiving data frames, the client goes back to sleep until the next ATIM window.
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13 MAC and Physical Layers The technology of any wireless LAN is the same from one network to the next; but how manufacturer utilizes that technology differs. Some of the characteristics of the MAC and Physical layers have commonalities to all wireless LAN products, no matter the manufacturer.
13.1 Communicating with Wireless LANs Wireless LAN equipment typically has configuration options that implement communication parameters. How these parameters are configured will impact the performance of the network. 13.1.1 Frames: Wireless vs Ethernet One common misconception about wireless LANs is the use of 802.3 Ethernet frames. This is not the case. When a wireless client joins a network, the frames are passed to and from the client communication in a similar manner as any other IEEE Ethernet frames which feeds the misnomer, wireless Ethernet. Wireless LAN frames contain more information than common Ethernet frames. There are many variations of the IEEE 802 frames, but only one type of wireless frame. With 802.3 Ethernet frames, the frame type is chosen by the network administrator and it is used to send all data the wire. Wireless frames are all configured with the same overall frame format. Whether the frame is wireless LAN or Ethernet, it supports a maximum payload of 1500 bytes. The maximum size of an Ethernet frame is 1514 bytes while the maximum size for Wireless LAN frames are 1518 bytes.
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There are three different categories of frames with the frame format and types within these categories: Management Frames o Association request frame o Association response frame o Reassociation request frame o Reassociation response frame o Probe request frame o Probe response frame o Beacon frame o ATIM frame o Disassociation frame o Authentication frame o Deauthentication frame. Control Frames o Request to send (RTS) o Clear to send (CTS) o Acknowledgment (ACK) o Power-Save Poll (PS Poll) o Contention-Free End (CF End) o CF End + CF Ack. Data Frames. The primary difference between Ethernet and wireless LAN frames is that Ethernet frames are implemented at the Media Access Control (MAC) sub layer of the Data Link layer and the entire Physical layer. For wireless LANs, upper layer protocols are considered payload, allowing support of: IP IPX NetBEUI AppleTalk RIP DNS FTP Many others. Wireless LANs work on Layer 2. Copyright The Art of Service Brisbane, Australia │ Email:
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13.1.2 Collision Handling One major concern for wireless LAN implementations is collision, due to the fact that radio frequencies are a shared frequency. Wired networks also have to deal with collision, but have the means to determine if and when a collision happens. This is possible because of a protocol called Carrier Sense Multiple Access / Collision Detection (CSMA/CD). Since collisions cannot be detected on wireless LANs effectively, the best option is to avoid them. A similar protocol is CSMA/CA (CA stands for Collision Avoidance) was created for this purpose. The primary difference between the two protocols is the dependence of positive acknowledgments (ACKs) for CSMA/CA. When a client sends a packet, the receiving client returns an ACK. If the ACK is not received by the sending client, it assumes that a collision occurred and resends the data. Wireless LANs uses a large amount of control data; CSMA/CA is just a part of this overhead which uses almost 50% of the available bandwidth on the wireless LAN. Combined with other protocols such as RTS/CTS, overhead loads can contribute to an actual throughput of 5.0-5.5 Mbps on a typical 11 Mbps 802.11b wireless LAN. In a wired network, the overhead attributed to CSMA/CD on a average use network is about 30%. When the wired network becomes congested, the overhead can increase to 70%. A wireless network will remain at a constant 50-55% throughput when congested. Additionally, the CSMA/CA protocol will avoid the probability of collisions by sensing a busy network at the physical and logical layers. When this happens, random back off time is initialized to defer the client from transmitting a frame until the medium becomes idle.
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13.1.3 Fragmentation Another contributor to protocol overhead is the fragmentation of packets. Protocol efficiency is also reduced when no errors are observed. The IEEE 802.11 standard supports fragmentation. The benefit to fragmentation is the time required to retransmit data when errors occur is reduced. Fragmentation will breakup large packets into smaller segments and is used because of the premise that larger objects are easier to collide with. Each fragment requires its own headers and ACK, so the adjusting the fragmentation level will also adjust the amount of overhead associated with each transmitted packet. Fragmentation is only performed on unicast frames, not multicast and broadcast frames in order to minimize the impact of unnecessary overhead. Network administrators have to strike a balance between avoiding collisions by fragmenting to shorter packets and the increased overhead due to fragmentation. Some activities or focus areas that can be exploited to identify and maintain the optimal fragmentation rate include: A 1518 byte frame is the largest frame that can be sent on a wireless LAN segment without fragmentation Monitor the packet error rate and adjust fragmentation level manually Monitor the packet error rate and increase the fragmentation threshold when the rate is high. 13.1.4 Dynamic Rate Shifting (DRS) Dynamic Rate Shifting (DRS) and Adaptive Rate Selection (ARS) Copyright The Art of Service Brisbane, Australia │ Email:
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describe a method of dynamic speed adjustment on wireless LAN clients. An adjustment in speed occurs as distance increases between a client and access point or interference increases. DRS can impact network administrative concerns such as: Network throughput Cell sizes Power output Security Spread spectrum systems make discrete jumps to specified data rates, such as 1, 2, 5.5, and 11 Mbps. The signal strength will decrease until the data rate cannot be maintained as the distance increases between the access point and a client. Therefore the data rate will decrease as distance increases. The decrease is to the next specified data rate: 11 to 5.5 Mbps, 5 to 2, 2 to 1. Both FHSS and DSSS implement DRS. IT is required by IEEE 802.11, IEEE 802.11b, HomeRF and OpenAir standards. 13.1.5 Distributed Coordination Function 802.11 specifies that all clients on a wireless LAN contend for access on a RF using the CSMA/CA protocol. The access method to have this happen effectively is called Distributed Coordination Function (DCF). All service sets use DCF mode. 13.1.6 Point Coordination Function Wireless LANs can take advantage a polling mechanism to provide contention-free frame transfers. The transmission mode utilizing this mechanism is called Point Coordination Function (PCF). PCF creates a significant amount of overhead. DCF can be used without PCF, but PDF must have DCF to be used. DCF is scalable, however PCF limits the scalability by adding the overhead of polling frames. Copyright The Art of Service Brisbane, Australia │ Email:
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13.2 Interframe Spacing Understanding interface spacing aids in effectively using RTS/CTS, DCF, and PCF. 13.2.1 Types of Interframe Spacing In network language, space and time are often synonymous because spacing is often created be sending data in intervals. The longer the intervals, the longer the spacing. Three types of interframe spacing exists: SIFS - Short Interframe Space DIFS – Point Coordination Function Interframe Space PIFS – Distributed Coordination Function Interframe Space. Each type is used within a wireless LAN to send certain types of messages or manage the intervals when clients contend for the transmission medium. Measured in microseconds and used to manage deferment of the client's access to the network through levels of priority. The interframe spacing is based on different times for each type of 802.11 technology: IFS
DSSS
FHSS
Infrared
SIFS
10 µS
28 µS
7 µS
PIFS
30 µS
78 µS
15 µS
DIFS
50 µS
128 µS
23 µS
Everything is synchronized on a wireless network. Access points use standard time intervals, or spaces, to perform various tasks. Short Interframe Spaces (SIFS) are a fixed interframe space and the shortest of the three. They consist of the time spaces before and Copyright The Art of Service Brisbane, Australia │ Email:
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after certain types of messages, the most common are: RTS – Request-to-Send frame to reserve the medium for the client CTS – Clear-to-Send frame used to response to RTS frames form access points ACK – acknowledgment frame informing sending clients verification of data receipt. SIFS provides the highest level of priority on a wireless LAN because clients are constantly listening to the carrier sense waiting for it to be clear to transmit. The length of wait time is dependent on the function the client is attempting to perform. All functions fall into a spacing category. Tasks that have a high priority will fall within the SIFS category. If a client only has to wait for a short time for the medium to clear, it would have priority over clients having to wait longer periods of time. SIFS is therefore used for functions that require a short period of time but a high priority. PIFS has a longer interframe space and lower priority than SIFS. The only time PIFS is used is when the network is in point coordination function mode and only by access points. This ensures that the access point will always gain control of the transmission medium before clients in DCF mode. PCF will only work with DCF, so PIFS will only work when both PCF and DCF is used. DIFS is the longest fixed interframe space and the default for all 802.11-compliant devices using DCF. Every device on the network using DCF will have to wait until DIFS has expired before one can contend for the network. Since DIFS has the lowest priority, the possibility of collision rises as wireless devices contend for the network. Therefore, each device uses a random back off algorithm to determine how long to wait before sending information to avoid collision. The time period after DIFS is referred to as the contention period (CP). All clients in DCF mode will use the random back off algorithm Copyright The Art of Service Brisbane, Australia │ Email:
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during the contention period. Using the process, a client will choose a random number and multiply it by the slot time to get the length of time to wait. The clients on the network count down the slot times one at a time, performing a clear channel assessment after each slot. When the back off time expires, a clear channel assessment is done. If the medium is clear, transmission starts. The other clients sense the medium is busy and remember the remaining time of their random back off time. 13.2.2 Slot Times A slot time is a pre-programmed period of time on a wireless network. Slot times maintain time, in the same manner the second hand maintains time on a traditional clock. The slot time is dependent on the wireless technology used: FHSS Slot Time = 50 microseconds DSSS Slot Time = 20 microseconds Infrared Slot Time = 8 microseconds. PIFS = SIFS + 1 Slot Time DIFS = PIFS + 1 Slot Time 13.2.3 Communications Process When considering the PIFS process, it would seem that the access point would always have control over the medium. What prevents this from happening is the superframe. The superframe is a period of time consisting of three parts: Beacon Contention free period (CFP) Contention period (CP) The purpose of the superframe is to allow peaceful, fair co-existence between PCF and DCF mode clients. Copyright The Art of Service Brisbane, Australia │ Email:
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The superframe, and PIFS, occurs only when: The network is in point coordination function mode The access point is configured to perform polling Wireless clients have been configured to communicate they can be polled. The communication process using the superframe involves: A beacon is broadcasted from the access point during the CFP, the access point polls each wireless client to see if any need to transmit data If a client does need to transmit, it responds positively to the poll; if it does not, a null frame is the response Polling continues during the CFP The CFP ends beginning the CP and the access point ceases to poll wireless client. Clients using DCF mode are contending for the medium The superframe ends when the CP ends, and a new one begins with the next CFP. One thing to realize is that during CFP, the access point has total control of all functions on the wireless network. During CP, control is arbitrarily and randomly obtained by the clients on the network. When the wireless LAN is in DCF mode only, there is no polling and the process is simpler.
13.3 RTS/CTS Wireless networks use two carrier sense mechanisms: Physical carrier sense Virtual carrier sense. The physical carrier sense checks the signal strength, call the Received Signal Strength Indicator (RSSI) on the RF carrier signal to identify any active transmissions. The virtual carrier sense uses the Network Allocation Vector (NAV) as a timer on the client. The sending client will broadcast its intention to Copyright The Art of Service Brisbane, Australia │ Email:
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use the network by sending a frame to the destination client. The receiving client will set the NAV field to the time necessary for the client to complete its transmission, plus ACKs. The NAV field is set on all clients. The virtual carrier sense is implemented using the RTS/CTS protocol. RTS/CTS is an extension of CSMA/CA and allows clients to broadcast their intention to send data. RTS/CTS is turned off by default because of the overhead it can potentially create. However, if the wireless LAN is experiencing high latency times and low throughput, using RTS/CTS can increase the traffic flow and decreasing collision. Though it should not be done without careful analysis of the situation. 13.3.1 Configuring RTS/CTS Three configuration settings exist on most access points and nodes: Off On On with Threshold. When RTS/CTS is turned on, every packet through the network is announced and cleared between transmission and receiving nodes. Generally, RTS/CTS is used only to diagnose and troubleshoot network problems On with Thresholds allow administrators to determine which packets are announced and cleared. The thresholds can focus on larger packets since they are easier to identify and hit.
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prepares the digital signal for transmission. Within the 2.4 Ghz ISM band, networks can use several basic types of modulation, including: DBPSK – Differential Binary Phase Shift Key DQPSK -Differential Quadrature Phase Shift Key 2GFSC – 2 Gaussian Frequency Phase Shift Key 4GFSK – 4 Gaussian Frequency Phase Shift Key. They are used in conjunction with Barker Code and CCK spreading codes. Higher transmission speed use Orthogonal frequency division multiplexing (OFDM) as the spreading code and the following modulation methods: BPSK - Binary Phase Shift Key QPSK - Quadrature Phase Shift Key 16 and 64QAM.
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14 Troubleshooting Wireless Installations One of the biggest challenges of implementing wireless LAN solutions is the behavior of the radio frequency signals. Given the nature of wireless communication, the number of variables that can impact the solution is greatly increased over wired solutions; however, for most organizations and individuals, the benefits can outweigh the cost. With clear planning, most problems can be resolved rather quickly. Some of the most common problems that need to be corrected and compensated for include: Multipath Hidden node Near/far RF interference All-band interference System throughput Co-location throughput Weather.
14.1 Multipath Multipath is the composite of a primary signal with duplicate or echoed wave fronts caused by reflections of the wave. The fundamental understanding of multipath begins with line of sight. Visual line of sight (LOS) identifies the ability to see a specific object at a distance. The closer you are to the object in question, the less likely that obstacles will be present to prevent it from being seen. In the same fashion, radio communications has a line of sight, typically from a transmitting antenna to a receiving wireless device. However, RF LOS is different form visual LOS in the fact that the farther a RF signal travels, the wider it gets. Given this, the probability that obstacles will be found is much more likely. When objects are encountered, they can either reflect, diffract, or interfere with the signal. When a signal is reflected multiple wave Copyright The Art of Service Brisbane, Australia │ Email:
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fronts are created. The rough the surface of the reflection, the greater the differences in direction the reflected signals are going. This behavior is called multipath. Theoretically, the multiple waves are still going in the same general direction, however the individual waves will reach the target at different times. The time lapse between the primary signal and the last reflected signal is known as the delay spread. 14.1.1 Effect of Multipath Several effects can be cause by multipath behavior, which include: Decreased Signal Amplitude (downfade) Corruption Nulling Increased Signal Amplitude (upfade). Each of these conditions affect the transmission of the RF signal differently. When an RF wave arrives at the target, several reflected waves may arrive at the same time. The amplitude of these waves is added to the main RF wave. Reflected waves, out-of-phase with the main wave, can contribute to a decreased signal amplitude. This is often referred to as downfade and should be taken in consideration when performing a site survey. The same situation that can cause downfade can also corrupt the RF signal when the conditions are more extreme. Corruption happen when the delay spread is so great that most of the information carried on the wave can be read, but not all. One of the contributing factors is noise and is caused by the length of the delay spread. Noise will always exist and is described as the noise floor, the maximum amount of noise possible without interfering with the signal. As the signal reflects, it moves closer to the noise floor and represented by the signal-to-noise ratio (SNR). Eventually the ratio is so low, the signal is considered corrupted and the data must be resent. Copyright The Art of Service Brisbane, Australia │ Email:
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Sometimes, one or more reflected waves with such amplitude arrive at the target out of phase with the main wave that the signal's total amplitude is canceled. This condition is called nulling. When this happens, the data cannot be simply retransmitted. The transmitter, receiver, or reflective objects must be moved to resolve the problem. When multipath causes an RF signal to gain strength, the condition is called upfade. This occurs when the reflected waves arrive at the target in-phase with the main signal. No circumstance can be in place such that the signal can reach the target with a stronger signal than was transmitted; however it is possible that multipath occurs in such a way to be additive to the main signal that the total signal is stronger than it could have been without multipath. Additionally, the received RF signal will never be as large as the original signal transmitted because of path loss. Simply, as a signal travels through open space, the signal loses amplitude as it grows wide. 14.1.2 Troubleshooting Multipath Since radio waves cannot be seen, the only way to detect the occurrence of multipath is to identify the effects. Link budget calculation is performed to identify how much power output will be required to have a successful link between sites. If the link is not successful, it may indicate that multipath is occurring. Another method is to look for holes in RF coverage in a site survey. Coverage holes are the results of lack of coverage or overlapping and multipath reflections that null the main signal. Since multipath is the result of reflected RF waves, it makes sense that objects that reflect the signals easily should be removed or avoided, such as metal blinds, metal roofs or walls, and bodies of water. The solution may require that receiving or transmitting antennas be moved. Copyright The Art of Service Brisbane, Australia │ Email:
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14.1.3 Solutions for Multipath The best solution for compensating for multipath is antenna diversity. This method uses multiple antennas, inputs, and receivers to compensate for the conditions causing multiple. There are four types of antenna diversity, including: Antenna Diversity – not active Switching Diversity Antenna Switching Diversity – active Phase Diversity. Antenna diversity that is not active is rarely used and identifies instances when multiple antennas support a single input. Switching Diversity has multiple antennas on multiple receivers. The receivers are switched based on signal strength. Antenna Switching Diversity is used by most WLAN manufacturers. Multiple antennas are used to support multiple inputs. The signal is received on only one antenna at a time. Phase Diversity is a patented proprietary technology that adjusts the phase of the antenna to the phase of the signal in order to maintain the quality of signal. The characteristics of antenna diversity work together to compensate multipath effects: The use of multiple antennas on multiple inputs to bring a signal to a single receiver. The RF signal is received through one antenna at a time. The receiving radio samples the incoming signal from all the antennas and chooses the higher quality signal. The radio transmits the next signal out of the antenna that was last used to receive the incoming signal. If the radio has to retransmit the signal, it will alternate antennas until it is successful. Each antenna can be used to transmit or receive, but not at the same time. So only one antenna can be used at Copyright The Art of Service Brisbane, Australia │ Email:
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any given time and only transmit or receive at that moment. This is called diversity transmission.
14.2 Hidden Node One of the biggest problems in wireless networking is collision detection. Since radio waves cannot be seen, it is impossible to detect collisions when they happen, but rather are discovered after they happen. Collisions happen when two or more network nodes sharing a communication medium transmit data simultaneously. Problems in transmission detection cause a condition called hidden node in wireless systems. Hidden node is encountered when at least one node is unable to sense one or more other nodes connected to the wireless LAN. This is often due to some obstacle of great distance between the nodes. The nodes cannot sense the other but can still connect with the access point, they can both initiate a communication with the access point at the same time causing a collision. Because the two signals collide, they are not received and are retransmitted and the probability of another collision is high. 14.2.1 Troubleshooting Hidden Node The main symptom of hidden node is degraded throughput over the wireless network. Most complaints related to hidden node is network sluggishness because hidden node problems and decrease throughput up to 40%. Wireless LANs that use CSMA/CA protocol already have an overhead of 50%. Hidden node will cause almost half of the remaining throughput to be lost. The mobility of wireless devices makes hidden node problems inevitable.
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14.2.2 Solutions for Hidden Node Identifying a hidden node problem is only the beginning: the offending node(s) have to be found. This search is typically trial and error. Once the nodes have been located, several remedies can be used: RTS/CTS Increased power Obstacle removal Moving the node. Using RTS/CTS is not really a solution to the hidden node problem, but is rather a method of reducing the negative impact of hidden nodes on the network. The network throughput can be severely impacted by the excessive collisions caused by hidden nodes. This is possible because the protocol involves prompts to complete the transmission. Increasing the power to the nodes can solve the problem by allowing the call around each node to increase in size. The larger the cell, the greater the chance of detection. A cement or steel walls are common obstacles contributing to the hidden node problem. Even the increase of power will not overcome these obstacles. Though unlikely, removal of these obstacles will resolve the problem. For a more practical approach than removal of walls, moving the nodes so that they can sense each other is another option. Extending the wireless LAN to add proper coverage can also help, including adding access points.
14.3 Near/Far Near/Far problems exist when multiple client nodes are very near to the access point and have high power settings and at least one client node is much farther away and using a lower power setting. The result is the farthest client nodes using low power cannot be heard over the traffic created by the closer high-powered clients. Copyright The Art of Service Brisbane, Australia │ Email:
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14.3.1 Troubleshooting Near/Far Typically, near/far problems can be handled by revisiting network design, the location of stations on the wireless network, and the transmission output power of each node. This will provide the clues towards why nodes are having connectivity problems. Using a wireless sniffer will detect near/far problems by picking up the transmissions from all stations it hears. By moving around the network looking for stations with a weak signal because of its relation to the access point and other nodes. 14.3.2 Solutions for Near/Far The CSMA/CA protocol solves much of the problem with no intervention from the administrator. If a node can hear another node transmitting, it will stop its own transmissions. Other solutions that can be used if the problem persists are: Increase power to the remote node Decrease power of local nodes Move the remote node closer to the access point. Moving the access node closer to the remote node is also another option but is also an indicator of a flawed design or site survey.
14.4 System Throughput Many factors impact the throughput on a wireless LAN, including: The amount and type of interference Overhead for encrypting and decrypting data Overhead for VPN tunnels Greater distances between transmitters and receivers Hardware limitations Type of spread spectrum technology used Use of proprietary data link layer protocols Overhead for fragmentation Copyright The Art of Service Brisbane, Australia │ Email:
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Packet size limitations Overhead for collision avoidance RTS/CTS protocol use The number of users access the medium at the same time Polling on the wireless network using PCF.
14.5 Co-location Throughput Co-location is a common technique used to provide more bandwidth and throughput in a given area. Wireless LANs can have three nonoverlapping RF channels (1,6,and 11). These three channels can be used to co-locate multiple access points in a given physical area using 802.11 equipment. When co-locating access points, it is recommended that the same spread spectrum technology is used for all access points, as well as the same vendor for the hardware. In theory, the use of three non-overlapping channels would allow one access point to be setup for each channel without any overlap in the RF band usages. Normal throughput will be available for all colocated access points with no interference, of degradation due to the adjacent channels. In reality, there exists some overlap between channels 1 and 6, as well as 6 and 11. The overlap is due to the access points transmitting at the same high output power and being located relatively close to each other. The result is a detrimental effect on all three access points. This effect can be an evenly distributed reduction of throughput on the three access points, or an uneven distribution on the three. 14.5.1 Solutions for Co-Location Throughput Problems The impact on the throughput may not be detrimental enough to warrant any concern, so a solution may not be sought. If a workaround is required, there are several options. Copyright The Art of Service Brisbane, Australia │ Email:
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The easiest option is to reduce the number of co-located access points to two, instead of three, using the channels 1 and 11. This will ensure there is no overlap at all between the two access points. The use of 802.11a equipment, which supports 5 GHz UNII bands, is another option. Using these devices in combination with 802.11b equipment working in 2.4 GHz ISM band provides more options. In essence, a network can have two or three 802.11b access points and 8 inside-use 802.11a access points, providing an incredible amount of throughput in the same physical space.
14.6 Types of Interference The behavioral tendencies of the RF technology are unpredictable. Because of this, there are several types of interference that must be dealt with during the implementation and management of a wireless LAN, including: Narrowband All-band RF signal degradation Adjacent channel interference Co-channel interference. 14.6.1 Narrowband Narrowband RF and spread spectrum technology are highly divergent solutions. As such, the signals from narrowband transmitters can interrupt, even disrupt the RF signals emitted from a spread spectrum device. Some of the conditions that influence the interruption include: Output power Frequency width Consistency. Narrowband signals do not disrupt RF signals across the entire RF band, rather only a single carrier frequency (1 MHz in a 22 MHZ channel) will be disrupted. Spread spectrum technologies usually work around the problem without additional administration of configuration. Copyright The Art of Service Brisbane, Australia │ Email:
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Spectrum analyzers aid in locating and measuring narrowband RF signals. There are hardware and software implementations of these tools. The first thing to do to remedy a narrowband RF interference problem is to find the source of the interference using spectrum analyzer. Essentially, as the spectrum analyzer gets closer to the interference source, the RF signal peaks on the display screen. When the source has been found, the option for resolving the problem can include: Removing the source Shielding the source Reconfiguring the wireless LAN. 14.6.2 All-Band Interference Any signal that interferes with the RF band from one end of the spectrum to the other is called all-band interference. Bluetooth is considered an all-band interference with 802.11 wireless networks. In homes and offices, microwaves can be a source of all-band interference. When all-band interference is present, the best solution is to change to a different technology, such as from 802.11b to 802.11a. This may not be the best option given the cost, so the next best option is to identify the source of the interference and remove it. Discovery of the source of all-band interference is significantly harder than finding the source of narrowband interference as are range of signals with varying amplitudes are being analyzed. 14.6.3 Weather The performance of a wireless LAN can be affected by severely adverse weather conditions. Most common weather situations will not have any impact; however extreme occurrences of wind, fog, and even smog can cause degradation and downtime of the wireless LAN. Copyright The Art of Service Brisbane, Australia │ Email:
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A radome can be used to protect antennas from the elements, with a drain hole to handle condensation. Rain and ice can accumulate on the elements and detune the performance. Torrential rain can create from .05 to .5 db/km attenuation. Thick fog can create from .02 to .07 db/km attenuation. Actual falling rain may not be the problem itself, but water droplets on the leaves of trees and other objects can affect performance. Strong winds can affect the positioning of outdoor antennas, specifically impacting any point-to-point solution that requires exact positioning. The wind can easily move one or both antennas to completely degrade the signal in an effect called “antenna wind loading.” The settling of a very thick fog, or smog, results in the air slowing down radically and separating into layers. This is called stratification and causes the RF signal to bend as it goes through the layers. Lightning strikes can hit a wireless LAN component or nearby object and physically damage equipment. Lightning also can charge the air that RF waves travel through, having the same effect that the Aurora Borealis has on television and radio transmissions 14.6.4 Adjacent Channel and Co-Channel Interference Adjacent channels are those channels within the RF band that are being used side by side. An overlap exists because the center frequency for each channel 5 MHz apart but the bands are 22 MHz wide. Interference from adjacent channels occurs when two of more access points using overlapping channels are near enough that their coverage cells physical overlap. The problem requires a spectrum analyzer to show which channels are overlapping and how they are being used. Only two solutions exist for resolving adjacent channel interference: Copyright The Art of Service Brisbane, Australia │ Email:
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Move access points on the adjacent channels farther away from each other Turn the power down on each access point so that their cells do not overlap.
Similar to the effects of adjacent channel interference is co-channel interference, though the circumstances are different. In this case, the access points in conflict are on the same channel. To resolve the problem, a wireless network sniffer is required. The sniffer will show packets coming from each wireless LAN and the signal strength of those packets. This will identify how badly one wireless LAN is interfering with the next. There are two solutions to co-channel interference: Use a different, non-overlapping channel for each wireless LAN Moving the wireless LANs farther about so that access point cells do not overlap. If seamless routing is required, channel reuse is used to alleviate adjacent and co-channel interference.
14.7 Range Considerations Communication range is a crucial consideration when positioning wireless LAN hardware. The range of an RF link is affected by: Transmission power Antenna type Antenna location Environment. A higher output power for a transmitting radio can cause the signal to be transmitted at a greater distance. Reducing the range can be done by reducing the output power. The type of antenna can focus the RF energy into a tighter beam which will transmit the signal farther. Transmitting the signal into multiple directions will reduce the communication range. Copyright The Art of Service Brisbane, Australia │ Email:
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Noise in the environment can lead to a greater packet error rate. Interference can increase the noise floor, making maintaining a solid link less likely. Range is influenced by the transmission frequency. Using the same power, a 2.4 GHz system can reach further than a 5 GHz system.
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15 Wireless LAN Security 15.1 Wired Equivalent Privacy WEP is an encryption algorithm used for authenticating users by the Shared Key authentication process and for encrypting data packets over a wireless segment. It has some beneficial characteristics that lead to its adoption by 802.11, include: Exportable Reasonably strong Self-synchronizing Computational efficiently Optional. The algorithm is simple, utilizing a pseudo-random number generator (PRNG) and a RC4 stream cipher. WEP is actually a weak deterrent to security. All manufacturers of wireless hardware will load WEP. 15.1.1 WEP Keys At the heart of WEP are its keys, alphanumeric character strings implemented on network clients and infrastructure components. A WEP key is used to verify the identity of the authenticating station and to encrypt and decrypt data. When used to authenticate with an access point, the access point looks to see if the WEP key for the client matches the WEP key distribution system on the wireless LAN. WEP keys are 64-bit and 128-bit, but they are sometimes referred to as 48-bit and 108-bit keys because 24-bits are used for the Initialization Vector. Copyright The Art of Service Brisbane, Australia │ Email:
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Keys for WEP are typically static, meaning they never change. Most access points and clients can hold up to 4 WEP keys simultaneously allowing network segmentation. 15.1.2 Centralized Encryption Key Servers Centralized encryption key servers should be used to provide: Centralized hey generation Centralized key distribution Ongoing key rotation Reduced key management overhead. 15.1.3 Advanced Encryption Standard RC4 stream cipher is a fast method of encryption and decryption. Advance Encryption Standard (AES) is a replacement for RC4 used in WEP. AES used the Rjindale algorithm in specified key lengths: 128, 192, and 256-bit lengths. The National Institute of Standards and Technology adopted AES for the Federal Information Process Standard (FIPS). 15.1.4 Filtering Filtering can be used in addition to WEP and AES. IT intention is to keep out what is not wanted while letting in what is wanted. Three basic types of filtering exist: SSID filtering MAC address filtering Protocol filtering. SSID filtering is the most basic form of access control, where the SSID of the wireless client must match the SSID on the access point Copyright The Art of Service Brisbane, Australia │ Email:
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or other clients on the network. A SSID is easy to identify using a sniffer. The SSID is typically part of the beacon sent by access points, though some manufacturers have provided the ability to remove the SSID from the beacon or probe responses. Some common mistakes related to SSID include: Using the default SSID Basing the SSID on something company-related Using the SSID as a means of securing the network Unnecessarily broadcasting SSIDs. With MAC address filtering, the network administrator programs a list of allowable MAC addresses into each access point or in a RADIUS authentication server. Specific MAC addresses can also be blocked from the network. Protocol filtering simply prevents data packets using specific protocols from entering the network. 15.1.5 Wi-Fi Protected Access Since WEP is a weak means for security, a new means was required. Wi-Fi Protected Access (WPA) is based on the 802.11i standard and deals with WEP static encryption key issue. WPA uses Temporal Key Integrity Protocol (TKIP) which changes keys with every data packet. Its biggest flaw is WPA-PSK (Pre-Shared Key) allows the administrator to specify a password, which must be known by all users in order for users to connect to an access point. If the password is cracked, the network is vulnerable. However, WPA uses a 14 character random password or passphrase consisting of 5 randomly chosen words which makes the PSK virtually impossible to crack.
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15.2 Wireless LAN Attacks Four general types of attacks are often used against wireless LANs: Passive attacks Active attacks Jamming attacks Man-in-the-middle attacks. 15.2.1 Passive Attacks Passive attacks involve eavesdropping; a simple, yet effective, attack on wireless LANs. Essentially, the effort utilizes sniffers or customer application to gather information about the wireless network from a distance. 15.2.2 Active Attacks The purpose of an active attack is to perform some function on the network, including: Obtaining data on the network Using the access for malicious purposes Changing configurations. 15.2.3 Jamming The purpose of jamming is to shut down the wireless network. Jamming is done by overloading the RF signal, typically by using a high-powered RF signal generator or sweep generator. Jamming can be intentional or non-intentional. To resolve a jamming attack, the source of the jamming must be identified. Spectrum analyzers can be used for this purpose.
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15.2.4 Man-in-the-Middle Attacks A man-in-the-middle attack is comprised of two access points and used to hijack mobile clients. On an established and legitimate network, mobile clients are connected to the access point. In a MITM attack, a malicious hacker uses another access point with a stronger signal than the original access point. The wireless clients now associate to this stronger rogue access point. Some event must trigger the client’s switch to the rogue access point. Some clients may do so accidentally as part of any roaming down by the system. An all-band interference event can force roaming to happen to all clients in the area. Of course, the hacker must know and configure the rogue access point with the SSID used by the network.
15.3 Securing Wireless LANs A few things to look at when securing wireless LANs: Manually configure WPA setting Restrict available of WLAN clients Use WEP and WPA compliant hardware Manually configuring WLAN settings for WPA. Security solutions are emerging, including: Key management Wireless VPNs Key Hopping Technologies Temporal Key Integrity Protocol (TKIP) AES Based Solutions Wireless Gateways 802.1x and EAP. 15.3.1 Corporate Security Policy Copyright The Art of Service Brisbane, Australia │ Email:
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A well established security solution must have a security policy in place which covers what is to be secured, how it should be secured, and who has responsibility towards security and in what fashion. Several considerations need to be addressed by the security policy: Securing sensitive information Physical security Wireless LAN Equipment Inventory Security Audits Advances security solutions Public Wireless Network Limited and tracked access. 15.3.2 Security Solutions Some solutions that can be used independently or in combination: WEP/WPA Cell Sizing User Authentication Security Needs Security Tools Monitoring Rogue Hardware Switches Wireless DMZ.
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16 Fundamentals of Site Surveying In every wireless LAN implementation, a need exists to survey the site covered by wireless support. Some of the components addressed by the site survey include: Throughput needs Power accessibility Extendibility Application requirements Budget requirements Signal range.
16.1 Understanding Site Surveys An RF site survey is a map for successfully implementing a wireless network. It is the most important step in the process. The goal is in obtaining a quality survey, not in getting it done quickly. A comprehensive survey may take days or weeks to compile depending on the site. Conducting a survey is a task-by-task process to discover radio frequency behavior, coverage, interference, and hardware placement. The primary objective is to ensure mobile users experience continual, strong signal strength no matter where they are in the facility. Some expectations out of site surveys consist of: Discovering what kind of coverage is required Defining the contours of RF coverage from a source Identifying the interference expected based on the location of the access point and the coverage required Determining equipment placement The results of the survey are utilized in the design and installation process for the wireless solution. A proper site survey will address detailed specifications for: Copyright The Art of Service Brisbane, Australia │ Email:
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Coverage Interference sources Equipment placement Power considerations Wiring requirements.
16.2 Site Survey Preparation To prepare for the site survey, some information need to be gathered and decisions made. A few of the important topics to question before performing the site survey are: Facilities Analysis Existing Networks Area Usages and Towers Purpose and Business Requirements Bandwidth and Roaming Requirements Available Resources Security Requirements.
16.2.1 Facility Analysis Identifying the type of facility to be supported is critical to understand. Some considerations for understanding the facility are: The size of the facility The density of users The shape and terrain of the facility. Facilities may be several floors of a building or a single floor of several buildings spread across a campus. Structural considerations may identify limitations to RF communications. Additionally, the type of facility may identify other standards that must be addressed; for instance, government buildings, hospitals, schools, and transportation all have additional regulations that specify technical, information, and personnel considerations that must be Copyright The Art of Service Brisbane, Australia │ Email:
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addressed if a wireless network exists. Equipment found in these facilities may have an impact on or may be impacted by the use of radio waves. The placement of this equipment is another consideration, such as warehouses where offices are usually at one end of the facility will large open spaces. 16.2.2 Existing Networks Understanding what is already in place for wired and wireless communication is very important. Most of the information will be obtained from the network administrator or manager. Some of the questions asked pertaining to existing networks are: What Network Operating Systems are in use? How many users (present and future) need simultaneous access to the wireless network? What is the bandwidth requirement? What protocols are in use over the wireless LAN? What channels and spread spectrum technologies are currently in use? What wireless security measures are in place? Where are the wired LAN connections points located in the facility? What are the client's expectations on the wireless LAN? What are the naming conventions used? A topology map of the current wired and wireless networks would assist in this step. 16.2.3 Area Usage and Towers The main concern is whether wireless usage will be primarily for indoor or outdoor use. If outdoor use is a consideration, weather is a concern, specifically in areas where tornadoes or hurricanes are highly probable occurrences. For bridging campuses, towers may be a concern. The structure of Copyright The Art of Service Brisbane, Australia │ Email:
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the tower, how it is built, where it is located, and even what is required to build it must be considered. Any structural buildings may require permits before construction. 16.2.4 Purpose and Business Requirements The reasons why the wireless network is required provide insight into what is necessary from temporary accommodations to permanent, and a growing networking base. 16.2.5 Bandwidth and Roaming Requirements The bandwidth and roaming requirements will determine the actual equipment required to implement the wireless network. Speed, range, and throughput are all major considerations.
16.3 Site Survey Equipment Many tools are required to conduct a successful site survey, including: Access points for testing Wireless components for testing Outdoor surveys Spectrum analysis Network analysis.
16.4 Conducting Site Surveys Indoor surveys should consider: AC power outlets and grounding points Wired network connectivity points Ladders or lifts required for mounting Potential obstructions for RF transmissions Cluttered areas. Copyright The Art of Service Brisbane, Australia │ Email:
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Outdoor surveys should consider: Trees, buildings, lakes, and other obstructions Seasonal trees that lose and grow foliage Visual and RF LOS between transmitters and receivers Link distances Weather hazards Tower accessibility and height Roof accessibility and height. 16.4.1 Gathering Information RF criteria to be gathered: Range and coverage patterns Data rate boundaries Documentation Throughput tests and capacity planning Interference sources Wired data connectivity and AC power requirements Outdoor antenna placement Spot checks. 16.4.2 Site Survey Report Some basic topics recommended for inclusion in site survey reports: Purpose and business requirements Methodology RF coverage areas Throughput Interference Problem areas Drawings Hardware placement Configuration information.
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17 Practice Exam 17.1 Questions Question 1 The amount of power has a direct affect on _____________. Choose all that apply. A) B) C) D)
Gain Link Viability Beamwidth Polarization
Question 2 What form of RF device is designed to generate and radiate RF signals? A) B) C) D)
Antennas Intentional radiators Access Points Transmitters
Question 3 Which member of the family of IEEE standards utilizes the 5GHz UNII frequency bands? A) B) C) D)
802.11 802.11b 802.11g 802.11a
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Question 4 If the power output for an antenna in a point-to-multipoint solution is 27, what is the allowable antenna gain to achieve the maximum EIRP? A) B) C) D)
15 dBi 9 dBi 29 dBi 36 dBi
Question 5 Which wireless network service set operates in ad hoc mode? A) B) C) D)
Extended Service Set Basic Service Set Infrastructure Free Service Set Independent Basic Service Set
Question 6 What frame category does the Acknowledge frame fall under? A) B) C) D)
Control frame Management frame Data frame Beacon Frame
Question 7 SSID are to wireless networks, what network names are to wired networks. A) This is never the case. B) Only when configured as the network name. C) This is always the case.
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Question 8 Which of the following statements are true? A) B) C) D)
Polling has a positive impact on network overhead TIM describe the time in sleep mode. Beacons are sent to identify when a client should wake up. Polling is best used with a IB Service Set
Question 9 The ability of a client to be able to identify the best access point to connect with while roaming through the networks is available because of ____________________. A) B) C) D)
Active scanning Reassociation process Passive scanning Roaming allowances
Question 10 How much blockage within the Fresnal Zone must be present before the RF signal is significantly disrupted? A) B) C) D)
10% 20% 35% 45%
Question 11 Wireless bridges are always half-duplex devices. A) The statement is always true B) Depends on the manufacture C) Bridges supporting 802.11a standards are full-duplex
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Question 12 IEEE has standardized the injected PoE voltage at ___________. A) B) C) D)
12 VDC 24 VDC 48 VDC 64 VDC
Question 13 What is the IEEE power output limit for a RF device running the middle UNII band. A) B) C) D)
40 mW 200 mW 250 mW 800 mW
Question 14 VPNs are typically found using ______________________. A) B) C) D)
Wireless Bridges Access Points Wireless Workgroup Bridges Wireless Residential Gateways
Question 15 If a hemispherical coverage pattern is required to provide wireless service to user, ______________ is the best choice for an antenna. A) B) C) D)
Omni0directional Yagi semi-directional Parabolic Dish Patch semi-directional
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Question 16 What is the power limit defined by the FCC for point-to-point communications? A) B) C) D)
3W 4W 5W 7W
Question 17 Which IEEE standard will only operate in the 2.4 GHz ISM band? A) B) C) D)
802.11 802.11a 802.11b 802.11g
Question 18 Which organization is responsible for wireless standards for companies which operate in London, England? A) B) C) D)
ETSI WECA IEEE FCC
Question 19 Wireless Workgroup Bridges are _______devices that multiple wired LAN clients to act as one. A) B) C) D)
Access points Bridge Client Receiver
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Question 20 On a point-to-point solution, if a gain of 21 dBi is required, how may dBm of power must the power output of the antenna be reduced? A) B) C) D)
25 dBm 21 dBm 15 dBm 5 dBm
Question 21 Which of the following describes the resistance to the current flow of power? A) B) C) D)
Resistor Ohms VSWR Impedance
Question 22 Which of the following is not specified as a license-free band? A) B) C) D)
902 MHz 2.4 GHz 3.6 GHz 5.0 GHz
Question 23 Which of the following DSSS channel combinations will not cause interference? A) B) C) D)
1 and 11 1, 6, and 10 2, 4, and 8 3 and 10
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Question 24 Which use of wireless LANs refers to the wireless connectivity services provided by telecommunications and cable companies to their customers, most of whom are in rural or hard to reach locations? A) B) C) D)
Point-to-point Last mile connectivity Point-to-multipoint Commercial wireless
Question 25 Why isn't WEP Authentication secure? A) B) C) D)
The method is too simple to be secure It is the default setting for all equipment The shared key is not large enough, or unique Both the plain text challenge and the encrypted challenge are easily obtained
Question 26 Which of the following features are commonly found on SOHO devices? Choose all that apply. A) B) C) D)
MAC filtering Telnet access Custom configuration applications 64-bit WEP
Question 27 Given an access point with 200 mW of output power connective through a 50 foot cable with 3 dB of loss to an antenna with 10 dBi of gain, what is the EIRP at the antenna in dBm? A) B) C) D)
27 dBm 29 dBm 30 dBm 33 dBm
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Question 28 The SSID is sent with what form of frame? A) B) C) D)
Association Request Frame Acceptance Frame Authentication Request Frame Beacon Management Frame
Question 29 What is a corrupt signal? A) B) C) D)
When the SNR is so low, the signal is lost to noise. When reflected waves decrease the signal amplitude When the signal is so out-of-phase the main signal is canceled When the signal is captured to gather more information.
Question 30 Which access point mode is not recommended for use because it causes a loss in throughput? A) B) C) D)
Root mode Repeater mode Bridge mode Ad hoc mode
Question 31 Which RF behavior describes the bending of radio waves around an object? A) B) C) D)
Defraction Refraction Reflection Scatterng
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Question 32 What is oscillation as it relates to wireless communications? A) The greatest level of adjustment available to semi-directional antennas B) An opposing force to polarization, diminishing the size of the electromagnetic field C) The transfer of energy from electric to magnetic fields and back again D) The widest beam spread for data transmissions
Question 33 Bluetooth technology is 802.11 compliant and can work on any wireless network. A) Never True B) Absolutely correct C) Bluetooth is not compliant to any IEEE 802.1x standard
Question 34 What should Site Surveys for indoor Wi-Fi networks consider? Choose all that apply? A) B) C) D)
Wired network connectivity points Distances of links Cluttered areas Large bodies of water
Question 35 As a network administrator, you have a need to limit the bandwidths used by wireless users. Which equipment must you include in your solution? A) B) C) D)
Access points Wireless residential gateway Wireless workgroup bridge Enterprise wireless gateway
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Question 36 Fragmentation is only performed on ________________. A) B) C) D)
Broadcast frames Unicast frames Data frames Multicast frames
Question 37 Which of the following is a viable solution to hidden mode problems? A) B) C) D)
Adding more access points Increasing power Decreasing power RTS/CTS
Question 38 The PIFS interframe spacing for FHSS has an interval of how many microseconds? A) B) C) D)
50 78 15 28
Question 39 Which organization is responsible for the regulations that govern wireless communications in the United States? A) B) C) D)
DoD WECA FCC IEEE
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Question 40 How many co-located access points are possible using FHSS technology? A) B) C) D)
3 12 26 79
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18 Answer Guide 18.1 Answers Question 1 Answer: A, B Reasoning: Gain and link viability are impacted the level of power applied. Question 2 Answer: B Reasoning: The intentional radiator is defined by the FCC as a device which generates and radiates RF signals. Question 3 Answer: D Reasoning: IEEE 802.11a provides greater speeds at the 5GHz UNII frequency bands but is not backwards compatible. Question 4 Answer: B Reasoning: The limit for PtMP EIRP is 5 watts or 36 dBm. If the antenna power output is 27 dBm, than the allowable gain is 9 dBi. Question 5 Answer: D Reasoning: Independent Basic Service Set works in ad hoc mode, since no access points are present. Question 6 Answer: A Reasoning: The ACK frame is part of the family of control frames. Question 7 Answer: C Reasoning: SSID are wireless networks versions of network names.
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Question 8 Answer: C Reasoning: Clients do listen for beacons to identify if they are next in the TIM list. Polling does not have a positive effect on network overhead as all clients and access points are consistently communicating extra information to ensure that polling works. In an IBSS, the problem worsens as each client is responsible for managing the TIM list. Question 9 Answer: B Reasoning: Reassociation processes ensure that a client continues to be connected to the network through multiple access points as the user roams through the network coverage area. Question 10 Answer: D Reasoning: Blockages of 20% - 40% in the Fresnel Zone have little or no effect on the RF signal. Question 11 Answer: A Reasoning: Wireless bridges will always be half-duplex. Question 12 Answer: C Reasoning: The IEEE standard is 48 VDC, though most manufacturers are using only 12 or 24 VDC. Question 13 Answer: B Reasoning: IEEE specifies the power output at 200mW, the FCC is 250mW. Question 14 Answer: D Reasoning: A Virtual Private Network is most commonly found for residential wireless solutions.
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Question 15 Answer: D Reasoning: A patch semi-directional antenna provides hemispheric coverage, while Yagi coverage is cylindrical. Question 16 Answer: B Reasoning: The power limit for point-to-point communications between antennas is 4 Watts per the FCC. Question 17 Answer: A, C Reasoning: Each of these work in only the 2.4 GHz ISM band. 802.11a works in the 5 GHz UNII band. Future versions are compatible on the 2.4 GHz ISM bands and higher bands as well. Question 18 Answer: A Reasoning: The European Telecommunications Standards Institute is the IEEE equivalent in Europe and defines the standards for telecommunications, including wireless LANs. Question 19 Answer: C Reasoning: A WGB aggregates multiple clients into a single client. Question 20 Answer: D Reasoning: The power at the antenna must be reduced by 1 dB below 30 for every 3 dBi above the initial 6 dBi of antenna gain. A requirement for 21 dBi of gain is 15 dBi over the initial 6, or 5 intervals of 3 dBi. For each interval, a reduction of 1 in the antenna power is required. Question 21 Answer: D Reasoning: Impedance is the resistance to power flow. Ohms is the measurement of that resistance, VSWR happens when impedance between nodes are mismatched. Copyright The Art of Service Brisbane, Australia │ Email:
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Question 22 Answer: C Reasoning: 902 MHz, 2.4 GHz, and 5.8 are ISM bands while all UNII bands are in the 5.0 GHz band. Question 23 Answer: A, D Reasoning: Channels must be at least 6 points apart. 1 and 11 comply as does 3 and 10. Question 24 Answer: B Reasoning: Last mile connectivity connects the commercial customer to the network backbone installed and managed by commercial vendors, such as telecommunications and cable companies. Question 25 Answer: D Reasoning: WEP is not secure because the plain text and encrypted challenge text can be sniffed out by hackers. Question 26 Answer: A, C, D Reasoning: Access to Telnet is available for enterprise solutions. Question 27 Answer: C Reasoning: 200 mW can be converted to 23 dBm. From here, simple addition and subtraction provides 23 dBm – 3 dB + 10 dBi = 30 dBm. Question 28 Answer: D Reasoning: The SSIS is always sent with the beacon so that network can identify the owning device. Question 29 Answer: A Reasoning: Corruption describes the condition when the signal strength is so close that the noise over takes it without canceling it Copyright The Art of Service Brisbane, Australia │ Email:
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out. Question 30 Answer: B Reasoning: Repeater mode is not recommended for several reasons, including reduced throughput. Question 31 Answer: A Reasoning: Reflecting is bouncing off an object. Refraction is the bending caused when going through an object. Scattering is a combination of all behaviors. Defection is the answer and occurs when the radio wave hits a dense object. Question 32 Answer: D Reasoning: Oscillation is the transfer of energy between electric and magnetic fields. Question 33 Answer: A Reasoning: Bluetooth is specified under IEEE 802.15 and is not compatible with the 802.11 family of standards. Question 34 Answer: A, C Reasoning: Link distances and large bodies are typically concerns on outdoor site surveys. Question 35 Answer: C Reasoning: Some wireless enterprise gateways support RBAC (role based access control) where user profiles can be created which describe the type of access is available to the user, such as rate limits. Question 36 Answer: B Reasoning: Unicast frames are the only data frames where fragmentation is performed, due the overhead created in the process. Copyright The Art of Service Brisbane, Australia │ Email:
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Question 37 Answer: B Reasoning: Increasing power is the best option. RTS/CTS does not solve the problem but will mitigate the effects of the problem. Setting up more access points is a possible solution, but only after increasing the power or moving the clients. Question 38 Answer: B Reasoning: 78 microseconds is the PIFS interframe spacing for FHSS. Question 39 Answer: C Reasoning: The Federal Communications Commission is responsible for the laws and regulations related to all communications technologies including wireless LANs. Question 40 Answer: D Reasoning: Up to 79 co-located access points are possible. 26 standard hop patterns have been defined by the FCC. The recommendation is a maximum of 12. The maximum number for DSSS is 3.
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19 References Certified Wireless Network Administrator Planet3 Wireless, Bremen Geargia: 2002 Online study resources:
www.ieee.org www.wi-fi.org CWNA information: http://www.cwnp.com/community/
Websites http://www.artofservice.com.au/ http://www.theartofservice.org/ http://www.theartofservice.com/
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INDEX* µ µS 92 128-bit keys 40-bit 35
35
A AC power outlet 85 AC power receptacles 59 AC power requirements Outdoor antenna Access Points 123, 126 accessories 3, 51, 62 Accessories for Wireless LAN 4, 62 ACKs 88-90, 96 Active attacks 114 Active scanning 70, 73, 82, 125 ad hoc mode 124, 130, 134 ad hoc network 81 adapter 45-6, 74 Adaptive Rate Selection (ARS) 90 Adjacent Channel 105, 108 adoption 32, 34, 111 Advance Encryption Standard (AES) 112 AES (Advance Encryption Standard) 112 air 12, 51, 108 all-band interference 37, 107 source of 107 Amazon 2 amplifiers 16, 62-5 power RF 65 right 63 amplitude 13-14, 62, 99-100, 107 Network 120 analysis, Answer 4, 134-9 Answer Guide 4, 134 antenna diversity 13, 101 antenna diversity work 101 antenna element 16, 30, 54 antenna gain 15-16, 30-1, 124, 136 Antenna Installation 3, 56 antenna power 136 antenna power output 134 antenna reception 58 Antenna Switching Diversity 101 Antenna type 55 Transmission power xf0b7 109
121
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antenna wind loading 108 53 antenna antenna Power 16 antennae 58 antennas 3, 12, 14-17, 30-1, 34, 40, 44, 51-8, 63-6, 101, 108-9, 123-4, 126, 128-9, 136 dangerous 58 detachable 40 dipole 51 directional 10, 53 diversity 40 dual 54 grid 53 high-gain 41, 56, 58 installing 56 mount 57 multiple 40, 101 radio technologies xf0b7 7 organization outdoor 58, 108 panel 66 patch semi-directional 136 right 51 single RF 67 transmitting 15, 31, 63, 98, 100 wireless LAN 51 antenna's axis 51 antennas perpendicular 57 architectures 19 Wireless metropolitan 19 area network, arrestors 64-5 ARS (Adaptive Rate Selection) 90 association 4, 74-5, 78, 83 association table 43, 75 ATIM frames 86, 88 ATIM windows 86 attacks, passive 114 attenuators 16, 64-5 authenticate 75-7, 111 authenticate clients 79 authentication 4, 74-9 mutual 79 user 78 authentication methods 4, 75, 78 authentication process 74-5 Authentication Protocols 4, 77, 79 Authentication Server 78 awake 86 Copyright The Art of Service Brisbane, Australia │ Email:
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B backwards 10, 33-4, 134 bands 18, 24, 27-9, 108, 136 license-free 27-8, 128 lower 29 upper 29-30 bandwidth 18, 28, 89, 105, 120, 131 Basic Service Set (BSS) 80-1, 86, 124, 134 beacons 26, 70-3, 83, 86, 95, 113, 125, 135, 137 beamwidth 16, 55, 58, 123 horizontal 16, 55 vertical 55 BER 72 blockage 15, 125, 135 blocks 57, 82 Bluetooth 37, 107, 131, 138 Bluetooth devices 19, 37 Bluetooth signal 37 bodies 31-2, 100 book 1-2, 6 boundaries 84-5 bridges 19, 40, 42-4, 60, 62-4, 67, 125, 127 non-root 42-3 root 42 standard 43-4 workgroup 43-4, 64 Brisbane 2, 5-8, 11, 24, 26, 30-1, 50, 55-6, 69, 92, 97, 106, 110, 122, 129, 132-3 [1] broadcast 26, 95-6 BSS, see Basic Service Set buildings 10, 13, 19, 35, 52, 57, 118, 121 bytes 87 C CA 89 cables 12, 14, 16, 40, 44-5, 51, 59, 61-2, 66, 68-9 CAM (continuous aware mode) 85 card 44-6 radio 40 carrier 21 carrier sense, virtual 95-6 Cat5 cable 60-1 catalogue 2 cells 81-2, 84, 103, 109 single 81 certification 35 Copyright The Art of Service Brisbane, Australia │ Email:
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Certified Wireless Network Administrator (CWNA) 1, 3, 7-8 Certified Wireless Network Administrator discipline 1 Certified Wireless Network Administrator Exam 1 Certified Wireless Network Administrator methods 1 Certified Wireless Network Administrator Planet3 Wireless 140 CFP (Contention free period) 94-5 CFR (Codes of Federal Regulation) 20 channel assessment, clear 94 channels 22-5, 28, 72, 83-4, 105-6, 108-9, 119, 137 overlapping wireless LAN 47 chips 23, 33 circuit 22, 67, 69 client associates 83 client communication 87 client connectivity 40 client devices 42-3, 46, 53, 63 single 43 client matches 111 client node 103 client reassociating 82 client responses 78 client roams 84 clients 39-40, 43-4, 57, 70-2, 74-86, 89, 91, 93-6, 112-13, 115, 125, 127, 135, 139 destination 96 high-powered 103 sending 89, 95 single 136 clients contend 92 client's expectations 119 clients sense 94 clock 71 co-channel interference 108-9 coaxial transmission lines 64 codes 23, 97 Codes of Federal Regulation (CFR) 20 collisions 22, 89, 93, 102 communications 39, 42, 68, 71, 80, 85, 102 compliant 19, 25, 34, 131 compliant devices 32, 34 concepts 1, 3, 15, 36, 53 conditions 99-102, 106, 137 configuration 25, 34, 44-5, 59, 63-4, 66, 76, 80, 106 point-to-multipoint 42 connect 10, 39-40, 42-3, 45, 47, 73-4, 80, 85, 102, 113, 125 connection 11, 14, 30, 40, 44-5, 47, 62, 72, 78, 82-4 point-to-point 38 Copyright The Art of Service Brisbane, Australia │ Email:
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connectivity 10-11, 19, 46-9, 74, 83-4 connector types 65, 68 connectors 16, 58, 63, 65, 68-9 standard 69 Contention free period, see CFP contention period, see CP continuous aware mode (CAM) 85 control 41, 77, 94-5, 112, 138 conversation 82 core network 41, 84 cost 9, 34, 64, 98, 107 coverage 52-4, 84, 100, 103, 117 CP (contention period) 93-5 CSMA/CA 89, 96 CSMA/CA protocol 89, 91, 102, 104 CSMA/CD 89 Custom configuration applications 41-2, 129 CWNA, see Certified Wireless Network Administrator D Data frame 86, 124, 132, 138 data-link layer networks 10 data packets 113 data rates 22-3, 25, 32-4, 81, 91 data signal 18, 23 data speeds 33, 81 data throughput 22, 25 data transfer rates 9-10 dB 17, 30-1, 55, 62-3, 67, 129, 136-7 db/km attenuation 108 dBi 17, 30-1, 124, 128-9, 134, 136-7 initial 30 dBi of antenna gain 31, 136 dBm 17, 30-1, 63, 128-9, 134, 137 DC power 59 DC power jack, regular 60 DC voltage 60-2, 65, 68 DCF (Distributed Coordination Function) DCF mode 91, 93, 95 decibels 17, 56 Decreasing power 132 defraction 13, 130 degradation 44, 105, 107 RF signal 106 degrees 55 design revisiting network 104
91-3
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Point-to-multipoint 52 designations 6 destroy signals 13 detachable antennas 40, 43 devices 4, 13, 20-1, 23, 25, 29, 32-3, 35, 40-6, 50, 54, 59-60, 62, 64-7, 85-6, 93 [4] DHCP (Dynamic host configuration protocol) 48 differences, primary 34, 88-9 diffraction 13, 15 DIFS 92-3 dipole 51-2 Direct Sequence Spread Spectrum, see DSSS directional, single 31 distance 41, 53-6, 62, 91, 98, 102, 104, 109, 114 Distributed Coordination Function, see DCF Distribution systems 81 doughnut 52 downfade 99 DRS (Dynamic Rate Shifting) 90-1 DSSS (Direct Sequence Spread Spectrum) 3, 20, 23-5, 32, 36, 91-2, 139 DSSS systems 23, 32, 71 DSSS uses 24-5 duplex, half 38-9 Dynamic host configuration protocol (DHCP) 48 Dynamic Rate Shifting, see DRS E EAP (Extensible Authentication Protocol) 77-8, 115 EAP authentication 78 earth 13, 55 eBook 2 free 2 EIRP (Equivalent Isotropically Radiated Power) 16-17, 30-1, 56, 129 energy 52, 54 electrical 15 Enterprise wireless gateways 48-9 Enterprise Wireless Gateways 3, 48-9 enterprises 9 environments 76, 82, 85, 110 Equivalent Isotropically Radiated Power, see EIRP errors 90, 103 ESS (Extended Service Set) 81, 124 Ethernet 36, 39, 45, 48, 59, 87-8 Ethernet frames 87-8 ETSI (European Telecommunications Standards Institute) 24, 35-6, 127, 136 Copyright The Art of Service Brisbane, Australia │ Email:
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European Telecommunications Standards Institute, see ETSI Evolution of Wireless LANs 3, 9 exam 1, 7-8 Extended Service Set (ESS) 81, 124 Extensible Authentication Protocol, see EAP F facility 117-19 farther 81, 83, 98, 103 fault 61-2 fault protection 61-2 FCC (Federal Communications Commission) 3, 9, 16-17, 20-4, 27-31, 34, 37, 68, 127, 132, 134-6, 139 FCC power output 30 Federal Communications Commission, see FCC Federal Information Process Standard (FIPS) 112 FHSS (Frequency Hopping Spread Spectrum) 3, 20-1, 23, 25, 32, 91-2 FHSS systems 21, 23-5, 32, 71 fields 54 electrical 51, 54 filtering 112-13 FIPS (Federal Information Process Standard) 112 fog, thick 108 forwards 78 fragmentation 90, 132, 138 fragmentation level 90 frame format 87-8 frames 70, 86-9, 95-6, 124, 130 probe response 73, 88 Free Space Path Loss 55 Frensel Zone 15 frequencies 13, 15, 18, 20-3, 28-9, 52, 108 highest 65, 67 licensed 20 radio 9, 12, 89 frequency bands 20-1, 28 frequency hopping 20-1, 24-5, 71 Frequency Hopping Spread Spectrum, see FHSS frequency hopping systems 21-2 frequency response 63, 67-8 Fresnel Zone 15, 57, 135 functionality 43, 45-7, 78 functions 45, 67, 71, 82, 93, 95, 114 variable power output 41 G gain
10, 12, 16-17, 30, 51-2, 54, 63, 123, 128-9, 134, 136 Copyright The Art of Service Brisbane, Australia │ Email:
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gateways 47-50, 81, 84, 115 enterprise 49 residential 47-8, 131 Gaussian Frequency Phase Shift Key 97 Ghz 22, 24, 27-8, 63, 69 GHz 24, 29-30, 33, 128, 137 GHz frequencies 33 Ghz ISM band 22-3, 33, 97 GHz ISM band 29-30, 32-3, 37, 106, 127, 136 GHz networks and FHSS systems 37 GHz system 110 GHz UNII bands 30, 33, 106, 136 ground 54, 64-6 H hardware 16, 39-40, 60, 72, 80, 105, 107 heat 13, 57-8 hidden node 4, 98, 102-3 hidden node problems 102-3 High gain antennas 52 high-powered RF signal generator 114 Highly-Directional Antennas 53 HiperLAN 36 HomeRF 37 hop sequences 21, 23, 26, 71 hop times 21-2 hops 21, 37 I IBSS (Independent Basic Service Set) 81, 86, 124, 135 IEEE (Institute of Electrical and Electronics Engineers) 3, 9, 19, 21-3, 29, 31-2, 34, 36, 61, 64, 75-6, 87, 90-1, 126-7, 132, 135-6 [1] IEEE power output limit 126 impact network 91 impedance 13-14, 63, 65-9, 128, 136 Obstacle removal xf0b7 103 Increased power Increasing power 132, 139 Independent Basic Service Set, see IBSS indoor Wi-Fi networks 131 Industrial, Scientific, and Medical (ISM) 27-8 industry 59, 69 Infrared Data Association (IrDA) 38 Infrastructure Devices for Wireless LANs 3, 39 injector 60 insertion loss 65, 67-8 Institute of Electrical and Electronics Engineers, see IEEE intention 6, 95-6, 112 Copyright The Art of Service Brisbane, Australia │ Email:
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intentional radiator 16, 30-1, 123, 134 Power 16 intentional radiator Intentional radiators and Equivalent Isotropically Radiated Power interference 4, 15, 21, 23-4, 28, 35, 91, 105-8, 110, 117, 128 narrow band 21, 24-5 interoperability 9-10, 25, 35-6 intervals 92, 132, 136 standard time 92 IR 38 IrDA (Infrared Data Association) 38 ISM (Industrial, Scientific, and Medical) 27-8 ISM bands 29, 137 isolation 67 J jamming K keys
16
114
35, 111-13
L Large sized networks 60 laws 9, 20, 27, 31, 34, 139 layer 42, 47, 74, 78, 84, 88, 108 legitimate network 115 liability 6 license 27-8 lightning 64, 108 lightning arrestors 64-6 limitations 29-30, 41, 61, 118 line 15, 65, 67, 98 Line of Sight (LOS) 15, 98 link 2, 15, 30-1, 41, 78-9, 100, 131 high-power point-to-point wireless 20 local area networks 37 Antenna 109 locations, LOS, see Line of Sight loss 6, 12, 14, 16, 55-6, 69, 129-30 M MAC (Media Access Control) 26, 40, 43, 46, 71, 88, 113 maintenance 58 Man-in-the-Middle Attacks 115 manufacturers 6, 9-10, 25, 34, 41, 44-6, 59, 61, 68, 87, 111, 113, 135 match 45, 65, 68, 71, 77, 112 maximum output power 29 maximum power input 67 Copyright The Art of Service Brisbane, Australia │ Email:
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measure output power 17 Media Access Control, see MAC medium 53, 79, 84, 89, 93-4, 105 medium-sized networks 60 medium-traffic networks 22 meters 56, 59 Mhz 23-5, 27 MHz 21, 28-9, 37, 106, 108, 128, 137 microseconds 22, 65, 92, 94, 132, 139 milliwatts 17 MIMO (Multiple Input Multiple Output) 34 mobile clients 115 hijack 115 Mobile IP network 79 mobility 9-10, 102 models 41, 62, 67 walk-up point-to-point user 38 modes 39, 42-3, 130 infrastructure 80-1 power management 85 Power 85 Modulation 4, 96 Most amplifiers 62-3 Most highly-directional antennas 53 mounting 57, 67-8 ms 22 multipath 4, 98-101 multipath effects 13, 99, 101 multiple antennas support 101 multiple clients 44, 136 Multiple Input Multiple Output (MIMO) 34 multiple inputs 40, 101 multiple wired LAN clients 43, 127 mW 17, 25, 29-30, 37, 63, 126, 137 mW of output power 37, 129 N Narrowband signals 106 narrowband transmissions 18 NAT (Network address translations) 48 NAV (Network Allocation Vector) 95 NAV field 96 Near/Far 4, 103-4 near/far problems 104 network 9, 11, 20, 39-40, 44, 46-7, 60, 63-5, 70-5, 78-80, 82-7, 89, 92-7, 103-4, 113-15, 119 [9] Network address translations (NAT) 48 Copyright The Art of Service Brisbane, Australia │ Email:
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network administration 70 network administrator programs 113 Network administrators 87, 90, 119, 131 Network Allocation Vector (NAV) 95 Network Architecture 4, 7, 9, 70 network authentication 78 network backbone 137 wired 39 network clients 86, 111 network connections 45 network connectivity 81 losing 82 network coverage area 135 network devices 79 network environment 51 network language 92 network management 84 network names 70, 124, 134 network nodes 102 Network Operating Systems 119 network overhead 125, 135 network restrictions 41 network segmentation 112 network sluggishness 102 network throughput 103 network types 41 113-14 network networking base, growing 120 nodes 96, 102-4, 136 farthest client 103 multiple client 103 remote 104 noise 18, 99, 110, 130, 137 noise floor 18, 99, 110 notation 75 mathematical 17 notebook computers 44, 46 O objects 13, 15, 64, 90, 98, 100, 108, 130, 138 obstacles 98, 102-3 OFDM (Orthogonal Frequency Division Multiplexing) ohms 14, 63, 66-8, 128, 136 omni-directional antennas 10, 16, 30, 51-3, 56 online 2, 140 Open System authentication 76 Open System Authentication 76
33, 97
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OpenAir 10, 25, 38 operation 29, 32 options, best 11, 65, 89, 107, 139 organizations 3, 10-11, 34, 36, 38, 98, 127, 132 orientation 57 Orthogonal Frequency Division Multiplexing (OFDM) outdoors 29, 52 output connectors 66 output ports 60, 67-8 output power 37, 67, 109, 129 high 105 radio cards Variable 40, 43 overhead 89-91, 96, 102, 104, 138 Grounding 58 overhead power lines overpowering 18
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P packet transmissions 82 packets 72, 89-90, 96, 109 buffer 86 parallel 54-5, 57, 68 parameters, configurable 47 password 78-9, 113 PAT (Port address translation) 48 Path Loss 55, 100 PC cards 44-6, 74 PCF (Point Coordination Function) 91-3, 105 PCF and DCF mode clients 94 PCMCIA cards 44-5, 54 PCMCIA slots 40 PCS (Personal communications system) 19 PDAs 44-5 peak power 18 low 18 peer-to-peer network 82 perpendicular 54-5 Personal communications system (PCS) 19 phase 13, 100-1 picker 60-1 PIFS 92-5 pins 59 placement 53, 56, 64, 119 planes 54 plug-n-play 45 PoE (Power over Ethernet) 4, 59-61 PoE devices 59-60 Point Coordination Function, see PCF Copyright The Art of Service Brisbane, Australia │ Email:
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Point Coordination Function Interframe Space 92 Point Options 40 point-to-multipoint 10, 30, 129 point-to-multipoint wireless LANs 17 Point-to-Point 31 point-to-point, see PtP point-to-point communications 53, 127, 136 point-to-point connectivity 38 points 3, 22, 25, 29, 39-41, 43, 47, 49, 72-5, 79-85, 93, 105-6, 108-9, 112-13, 131-5, 139 [11] points 46 grounding 120 polarization 13, 54, 57, 123, 131 vertical 54 polling 95, 125, 135 polls 95 Port address translation (PAT) 48 ports 60, 67 power 4, 14, 16-18, 25, 27-8, 30-1, 41, 47, 54-5, 58-9, 62, 65, 85-6, 103-4, 109-10, 128 [6] battery 86 calculating 16 conserve 85 low 37-8, 103 restore 62 uses 45 power classes 37 power considerations 16 Equipment placement xf0b7 118 power consumption 34 power flow 136 power levels 17 power limit 29-30, 127, 136 sliding 31 power lines 58 power loss 17 Power Management Features 4, 85 power meter 66 Power of Ethernet 59 power output 16, 25, 29-30, 66, 100, 124, 128, 135 track 66 Power over Ethernet, see PoE power requirements 60 Power-Save Poll 88 Power Save Polling 85 power save polling (PSP) 85 power settings, high 103 Copyright The Art of Service Brisbane, Australia │ Email:
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power supply 61 power utilization 27 power wireless LAN devices 59 powering 85 priority 92-3 high 93 PRNG (pseudo-random number generator) 111 problem 10, 14, 35, 44, 58, 85, 98, 100, 102-4, 106-9, 135, 139 process 12, 54, 72, 74-6, 78-9, 84, 86, 94-5, 117, 138 products 1, 6, 25, 32-3, 35-8 professionals 1 protocols 40, 77-9, 89, 103, 113, 119 Point-to-point 48 pseudo-random number generator (PRNG) 111 PSP (power save polling) 85 PSP mode 85-6 PtMP 30 PtMP links 30 PtMP Power Compensation Table 30 PtP (point-to-point) 10, 30-1, 42, 129 publisher 6 Q QoS (Quality of Service) quality, best signal 85 Quality of Service (QoS) quality signal 101
48 48
R Radiated Power 16 radiator, isotropic 17, 52 Radio Frequency (RF) 3, 12, 15, 27, 51, 69, 91, 98, 117 Radio Frequency Antennas 3, 51 radio waves 12-13, 15-16, 54, 100, 102, 119, 130, 138 radios 27, 29, 40, 101 RADIUS (Remote Authentication Dial-In User Service) 74, 78 rain 108 rate hop 37 packet error 90, 110 ratio, signal-to-noise 72, 99 RBAC (Role-Based Access Control) 49 RC4 stream cipher 111-12 Reasoning 134-9 reassociation 83 Received Signal Strength Indicator (RSSI) 95 receivers 15, 17, 72, 100-1 Copyright The Art of Service Brisbane, Australia │ Email:
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recommendation, high power 58 reconnection 72-3 redirect 64 refraction 13, 15, 130, 138 regulations 20-1, 27, 34, 64, 118, 132, 139 Remote Authentication Dial-In User Service (RADIUS) 74, 78 repeater mode 39, 43, 130, 138 repeaters 39-40, 43 request 74, 76, 78, 88 point's 78 probe 73 resistance 14, 67, 128, 136 signal's 23 resistant 24-5 response, positive 76-7 Restoring power 62 returned power 14 review 2 RF, see Radio Frequency RF antennas 53, 58 RF Antennas 3, 53 RF band 105-8 RF carrier signal 95 RF device 16, 123, 126 RF signal 14, 16, 30, 55, 62-4, 66-7, 99-101, 106, 108, 114, 123, 125, 134-5 RF signal interference 15 RF signal peaks 107 RF signal travels 98 RF splitters 66-8 RF waves 99-100 roam 71, 83-5 roaming 4, 73, 82-3, 115, 125 roaming requirements 118, 120 Role-Based Access Control (RBAC) 49 RSSI (Received Signal Strength Indicator) 95 RTS/CTS 4, 89, 92, 95-6, 132, 139 S scanning 70 passive 72, 125 Scattering 14, 138 secret, shared 77 security 51, 79-80, 84, 111, 113, 116 security policy 116 security solutions 115-16 semi-directional antennae 52 Copyright The Art of Service Brisbane, Australia │ Email:
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semi-directional antennas 11, 52-3, 131 placed 53 sense 100, 102-3 sequence 21, 23 servers 42, 78-9 Service Set Identifier 70 services 6, 11, 36, 48 set 23, 30, 81, 84, 96 basic service 80-1, 124 wireless network service 124 shared key authentication 76-7 Short Interframe Spaces, see SIFS SIFS (Short Interframe Spaces) 92-4 sight 15, 98 signal 12-18, 21, 51, 55-7, 62-3, 65, 67, 71-2, 83, 98-101, 106-9, 115, 130 amplified 62 corrupt 130 digital 97 disrupt RF 106 incoming 101 main 100, 130 measuring narrowband RF 107 multiple independent 66 primary 98-9 radio 12, 17 radio frequency 98 sending 53 single 66 total 100 weak 104 wired 12 signal amplitude 130 decreased 99 radio frequency's 12 Increased 99 signal beam 53 signal dispersion 55 signal farther 109 signal interception, preventing 51 signal leaking, reducing 51 signal level 63 signal loss 12, 62-3, 65, 67, 69 signal path 14, 68 signal separation 67 signal strength 12, 64, 72-3, 83, 91, 95, 101, 109, 137 strong 73, 117 Copyright The Art of Service Brisbane, Australia │ Email:
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signal strength Copyright 46 47 signal-to-noise ratios signal travels 55, 100 signals collide 102 SIM (Subscriber Identity Module) 79 site survey 99-100, 104, 117-18, 120 sleep 85-6 slot times 94 Small Office, Home Office (SOHO) 41 smog 107-8 sniffer 77, 109, 113-14 software 46 software network design xf0b7 7 SOHO (Small Office, Home Office) 41 SOHO devices 41, 129 solutions 10, 82, 98, 100-1, 103-5, 108-9, 116, 131-2, 139 architect wireless network 73 point-to-multipoint 124 point-to-point 108, 128 source 12, 38, 66, 107, 114 external power 12 spaces 92 spacing 92 interframe 4, 92 spatial streams 34 spectrum 18-20, 107 Spectrum analyzers 26, 107-8, 114 spectrum communication 18-19 spectrum technologies 3, 18-20, 28, 71, 104-6, 119 splitters 16, 60, 66-7 SSID 70-3, 81, 112-13, 115, 124, 130, 134 broadcast 73 Signal strength xf0b7 72 SSID value 70 standards 3, 9-10, 25, 27, 31-4, 36, 61, 75, 82, 85, 112, 118, 125, 136, 138 states 27, 75 stations 70-3, 104 strength, signal's 12 Subscriber Identity Module (SIM) 79 superframe 94-5 support 18, 28, 33, 36, 42, 49, 60, 65, 71, 78-9, 88, 101 Supported types of semi-directional antennas 52 surface 13-14, 55, 57, 99 survey 83, 117 switches active Ethernet 60 Copyright The Art of Service Brisbane, Australia │ Email:
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client's 115 Antenna 101 Switching Diversity, system transmits 22 systems 9, 14, 22, 25, 28, 32-3, 37, 115 higher-power 28 operating 45 T Table of Contents 3 technologies 9, 19, 21, 23, 32, 36, 81, 87, 92, 107, 112 frequency hopping 37 telecommunications 11, 129, 136-7 Temporal Key Integrity Protocol (TKIP) 113, 115 text 77, 137 thresholds 13, 96 manufacturer-defined signal strength 83 throughput 22, 25, 43-4, 62, 89, 102, 104-6, 120, 130 TIM (Traffic Indication Map) 71-3, 86, 125 TIM list 135 time 8, 17, 19-22, 32, 37, 43, 47, 58, 66-7, 72, 83, 86, 89-90, 92-4, 99, 101-2 [2] short 85, 93 time expires 22, 94 timestamp 71, 73 TKIP (Temporal Key Integrity Protocol) 113, 115 towers 119-20 trademarks 6 Traffic Indication Map, see TIM transmission medium 92-3 transmission output power 104 transmissions 14, 18, 22-3, 38, 71, 80-1, 94, 96-7, 99, 103-4 transmit 15, 28, 30, 77, 81, 93, 95, 101-2, 109 transmitted power 14 transmitters 14-15, 63-4, 100, 104, 121, 123 transmitting device 16, 21 trees 57, 108 troubleshoot network problems 96 tubes 65 tunnel 79-80, 84 types 4, 9, 20, 23, 44, 52-3, 56, 59-63, 68, 70, 78-9, 87-8, 92-3, 101, 106, 118 [4] basic 97, 112 U understanding 1, 16, 27, 41, 78, 118-19 Understanding Antennas 3, 15 UNII (Unlicensed National Information Infrastructure)
27, 29
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UNII bands 27-8, 33, 36, 137 unit 59 United States 9, 27, 31, 34, 36, 132 Unlicensed National Information Infrastructure (UNII) 27, 29 upfade 99-100 USB Adapters 45 USB Client 74 USB clients 45 users 11, 40, 47-8, 74, 78-9, 84, 113, 119, 126, 138 Using Power-over-Ethernet 60 utilities 46-7 V VDC 61, 126, 135 verification, informing sending clients 93 Virtual Private Network 135 Virtual private networks, see VPN voltage 61, 65 Voltage Standing Wave Ratio 3, 14 VPN (Virtual private networks) 48, 77, 79-80, 84, 126 VPN server 84 VSWR 3, 14, 65, 128, 136 W walls 13, 52, 100, 103 water 57-8, 100, 131 watts 17, 30-1, 134, 136 wave 13-14, 98-100 radio frequency 15 reflected 99-100, 130 WECA (Wireless Ethernet Compatibility Alliance) 10, 25, 35, 127, 132 WEP 37, 76, 111-13, 137 WEP key 76-7, 111-12 WGBs 43-4 Wi-Fi 9, 25, 32, 35 Wi-Fi Alliance 35 Wi-Fi Protected Access 113 wind 107-8 Varied types of 40, 43 wired connectivity, wired LAN connections points 119 Wired network connectivity points 131 Wired network connectivity points Ladders 120 wired network distribution 39 wired networks 10, 39, 80, 84, 89, 124 wireless 10-11, 40, 45, 47-8, 87, 109, 131 wireless bridges 3, 42-3, 58, 125-6, 135 wireless client 48, 70, 74-5, 80, 82-3, 85, 87, 95, 112, 115 Copyright The Art of Service Brisbane, Australia │ Email:
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poll 95 95 polling wireless client uses 85 wireless communications 98, 119, 131-2 wireless devices 13, 27, 44, 51, 59-60, 84, 86, 98, 102 manufacture 34 Wireless Ethernet Compatibility Alliance, see WECA Wireless frames 87 Wireless LAN antennas 51 Wireless LAN Association (WLANA) 35-6 Wireless LAN Attacks 4, 114 Wireless LAN Client Devices 3, 44 wireless LAN clients 70, 91 single collective 43 wireless LAN components 68-9, 108 wireless LAN connections 45, 78 wireless LAN devices 9, 29, 59, 68 Wireless LAN devices 20 wireless LAN devices, radio frequency spectrum 27 wireless LAN equipment 23, 27, 76 Wireless LAN frames 87 wireless LAN implementations 89, 117 Wireless LAN Interoperability Forum (WLIF) 10, 38 wireless LAN manufacturers 77 Wireless LAN Organizations and Standards 3, 27 Wireless LAN Security 4, 111 Wireless LAN Standards 9 wireless LANs 1, 15-17, 27, 31-2, 36, 67, 69-70, 74, 87-9, 92-3, 95-6, 102-4, 106-7, 109, 114, 119 [12] Wireless LANs 3-4, 9-10, 19, 29, 54, 62, 70, 87, 91, 102, 105 Wireless LANS 11, 27 Wireless LANs uses 10, 89 Wireless local area network (WLANs) 19-20 Wireless metropolitan area network (WMANs) 19-20 wireless network 10, 19-20, 35, 39, 41, 47, 51, 62, 70, 72, 79-80, 89, 94-5, 104-5, 114, 119-20 [6] wireless network sniffer 109 wireless networking 34, 36, 102 wireless nodes 47, 74-5 Wireless personal area network (WPANs) 19-20 wireless signal 12 wireless solutions 10-11, 27, 117 wireless technologies 1, 9, 34, 36, 94 Wireless wide area network (WWAN) 19-20 Wireless Wide Area Networks 20 wireless workgroup bridges 3, 43-4, 126-7, 131 WLAN clients Use WEP and WPA compliant hardware xf0b7 115 Copyright The Art of Service Brisbane, Australia │ Email:
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WLANA (Wireless LAN Association) 35-6 WLANs (Wireless local area network) 19-20 WLIF (Wireless LAN Interoperability Forum) 10, 38 WMANs (Wireless metropolitan area network) 19-20 WPANs (Wireless personal area network) 19-20 WWAN (Wireless wide area network) 19-20 www.emereo.org 2 www.theartofservice.com 140
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