Cisco - Introduction to Dial Services 201

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© 1999, Cisco Systems, Inc.

Introduction to Dial Services Session 201

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© 1999, Cisco Systems, Inc.

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Agenda • Circuit Types POTS, BRI, T1, E1, T3, E3 Signaling CAS, CCS, PRI

• Call Types Analog and Digital Calls “56K” Explained 201 1018_05F9_c2

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© 1999, Cisco Systems, Inc.

Dial Access Mobile User

Home User

POTS

POTS

Switch

PSTN

Switch

Switch

T1/E1/PRI

Enterprise / ISP Small Office

BRI

Local Loop 201 1018_05F9_c2

Switch

Public Switched Telephone Network

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Local Loop 4

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Plain Old Telephone Service (POTS) Mobile User

PSTN POTS

Switch

Switch

T1/E1/PRI

Enterprise / ISP

• Analog service delivered over a single pair of copper wires • Digitized at Central Office for transport • Ubiquitous, inexpensive and familiar 201 1018_05F9_c2

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Basic Rate Interface (BRI) Small Office

PSTN BRI

Switch

Switch

T1/E1/PRI

Enterprise / ISP

• Digital service delivered over same copper wire as POTS • Includes three separate data channels Two bearer or “B” channels operating at 64Kbps each and one signaling or “D” channel operating at 16Kbps 201 1018_05F9_c2

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T1, E1 and PRI Mobile User

Home User

POTS

POTS

PSTN

Switch

T1/E1/PRI

Switch

Switch

Enterprise / ISP Small Office

BRI

Switch

• Digital circuit used for dedicated access to the PSTN • Carried over two copper wire pairs 201 1018_05F9_c2

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© 1999, Cisco Systems, Inc.

T1 Frame 1

24

1 Channel Time Slot

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1

0

1

0

0

0

1

• 24 channels • 8 bits/channel • Each T1 data frame includes a framing bit • 24 channels * 8 bits + 1 framing bit = 193 bits per frame • 8kHz sampling frequency • 193 bits * 8,000 samples/sec = 1.544Mbps 201 1018_05F9_c2

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E1 Frame 11

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= Frame Synchronization 1 Channel Time Slot

• 32 channels

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1

0

1

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0

0

1

• 8 bits/channel • Each E1 frame includes a timeslot for frame Synchronization • 32 channels * 8 bits = 256 bits per frame • 8kHz sampling frequency • 256 bits * 8,000 samples/sec = 2.048Mbps 201 1018_05F9_c2

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PSTN Circuits—T3

• 28 T1s • 28 * 23 = 644 B channels • 28 * 24 = 672 DS0s

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PSTN Circuits—E3

• 16 E1s • 16 * 30 = 480 B channels • 16 * 30 = 480 DS0s

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Signaling

• A method for one end to inform the other end of control information Call setup, phone numbers, etc… Responsible for maintaining state information On-hook, off-hook, dial tone, etc…

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Channel Associated Signaling (CAS) T1 / CAS E1 / CAS

Signaling

Signaling

• Utilizes a signaling element for each channel T1 CAS—Robs the 8th bit of each timeslot in every 6th frame E1 CAS—Multiplexed in time slot 16

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Frame Synchronization 13

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Common Channel Signaling (CCS) Signaling

T1 / PRI E1 / PRI

Signaling

• Signaling is in a common dedicated 64K timeslot T1 PRI—Uses time slot 24 E1 PRI—Uses time slot 16 201 1018_05F9_c2

Frame Synchronization © 1999, Cisco Systems, Inc.

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PRI Circuits Signaling

T1 / PRI

23 ‘B’ channels for data and voice Single ‘D’ channel used for signaling

Signaling

E1 / PRI 30 ‘B’ channels for data and voice Single ‘D’ channel used for signaling 201 1018_05F9_c2

Frame Synchronization 15

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Circuit Comparisons Signaling

T1 / CAS 24 Channels Signaling

T1 / PRI 23 B-Channels / 1 D-Channel

E1 / CAS

Signaling

30 Channels / 1 Signaling Channel

E1 / PRI

Signaling

30 B-Channels / 1 D-Channel 201 1018_05F9_c2

Frame Synchronization © 1999, Cisco Systems, Inc.

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Remote Access Scenarios Mobile User

Home User

POTS

POTS

Switch

PSTN

Switch

Switch

T1/E1/PRI

Enterprise / ISP Small Office

BRI

Local Loop 201 1018_05F9_c2

Switch

Digital Network

Digital Local Loop 17

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Analog and Digital • Analog can be represented by a wide range of possible values Off, Low, Med, High

• Digital has a finite number of possible values Off, On 201 1018_05F9_c2

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Modulation and Demodulation • MOdulate—DEModulate The modem accepts digital data, typically from a PC, and converts it to an analog wave that can be transported over a normal analog phone line (and vice versa)

PSTN Digital

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Analog

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Analog to Analog

Analog Modem Switch

Switch

POTS

Analog

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Analog Modem

PSTN POTS

Digital

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Analog

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Analog to Digital Conversion

Analog Modem

Analog Modem

PSTN Switch

Switch

POTS

POTS

• Transmitting end is converted from analog to digital at the Central Office switch 201 1018_05F9_c2

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© 1999, Cisco Systems, Inc.

Digital to Analog Conversion

Analog Modem

Analog Modem

PSTN Switch

POTS

Switch

POTS

• Receiving end is converted from digital to analog at the Central Office switch 201 1018_05F9_c2

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Sampling and Noise

01100011

10110111

00101101

• Waveform is sampled 8,000 times per second and converted to one of 256 possible binary values • Analog sample may not correspond to one of the 256 possible binary values which results in noise (quantization) 201 1018_05F9_c2

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Analog to Digital “56K”

NAS with V.90

PSTN

Analog V.90 Modem Switch

Modem Switch

POTS

Analog

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T1/PRI

Digital

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“56K” Modem Call

• No A/D conversion since NAS modem is directly connected to the PSTN • Digital modems transmit digital values • Signal is only converted from digital to analog so no noise is introduced

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© 1999, Cisco Systems, Inc.

Client Only Receives “56K” No A/D Conversion POTS

PSTN Switch

Switch

Receive

56K Send

A/D Conversion POTS

Switch

PSTN Switch

Send 201 1018_05F9_c2

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T1/PRI

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T1/PRI

56K Receive 26

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“56K” Characteristics • Any analog to digital conversion will prevent 56K operation

Switch

Channel bank

Channel bank

Switch

Receive

Send

Switch

ü

Switch

Receive 201 1018_05F9_c2

56K

56K Send

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“56K” Limitations • Problems at the local loop Noisy analog lines caused by nearby power lines or other environmental factors

• Problems at the central-office Old equipment in the central-office may introduce additional A/D conversions Only obligated to provide a line capable of handling 4.8Kbps 201 1018_05F9_c2

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Federal Communications Commission Regulations • Sending a signal requires electrical power • The more power used, the greater chance of a problem called crosstalk • To avoid crosstalk, the FCC limits amount of power that can be used, limiting data throughput to 53Kbps

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Digital to Digital ISDN

Router

PSTN Terminal Adapter

Switch

NAS Switch

PRI

Digital

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ISDN Call

• Requires terminal adapter or router for client side • Requires ISDN circuits from Telco • BRI on client side • PRI on server side • All digital network 201 1018_05F9_c2

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© 1999, Cisco Systems, Inc.

Dial Services Review Mobile User

Home User

POTS

POTS

Switch

PSTN

Switch

Switch

T1/E1/PRI T3/E3

Enterprise / ISP Small Office

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BRI

Switch

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Please Complete Your Evaluation Form Session 201

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