Transmission and Switching PDF

8/3/2019 Transmission and Switching PDF

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Telecom Overview

Tuan May 2011


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Transmission & Switching: Switching in Telephone Network

Transmis

sion

Switching

Switching

Switching

Transm

ission


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Switching

Switching types

Connectionless/ connection oriented

Packet/circuit

Node 1 Node 2

Node 3

Access

Trunk Network

TerminalsTerminals

Access


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Circuit Switching

Cross-point

controlled

by CS

Cross-point

controlledby CS

TDMA

Time switch

- Makes switching between time slots

- In the figure incoming slot 3 is moved to

outgoing slot 3 for one voice direction

- Each coming timeslot stored in Speech Store (SS)

- Control store (CS) determines the order the slot

are read from SS

- The info in CS is determined during setupphase of the call

Space switch

- makes switching between PCM lines

- works with electronic gates controlled by CS

Circuit switching

- dedicated path

- constant delay/bandwidth

- voice/data

- paid by time

- examples: PSTN, VPN


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The Time-Space-Time (TST) Switch

Works in local exchange and subscriber stage

Performs PCM concentration, usually 10:1 3:1

Connects subscribers also to information tones

and test equipment

Time switch contains one bus for incoming and outgoing calls (full-duplex)

Subscrib

erstage

Space switch

Time switch

Time switch


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Switching: Telephone Exchange (Conceptual Model)

Switching

Matrix

Line Circuit

Line Circuit

Line Circuit

Line Circuit

Line Circuit

Control Computer

trunk lines +Inter-office

signaling

Register

Register

Register

Register


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Packet Switching

Node structure

Packet structure

Seq: sequence number

Op code: message/control

identifier

CRC: Cyclic Redundancy

Code

Note:

- source address

required for retransmission

in ARQ (Automatic Repeat reQuest)

- byte count could be also an

end flag


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Connection-oriented and Connectionless Switching

Connection oriented

- Applies same route

- QoS well defined

- Phases

- Connection setup

- Data transmission

- Release

- Packets received in same order

- Example: ATM, Frame Relay, PCM

Connectionless

- Use of different routes foreach packet possible

- Each packet have address fields

- QoS not guaranteed

- Packets may come in different order

- Example: IP (Internet Protocol),

TCP takes care of cleaning the mess


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Transfer Modes & Connections summarized

Circuit switching

Packet switching

Connection oriented

Connectionless

- hand-shaking

- strict error requirements

- for fast data transfer

- broadcasting

- modest error ratesoften accepted

- fast data in good channels

Transfer modes Connection types

- developed for data

- nowadays also for voice- Statistical multiplexing

- variable delays

- developed for voice

- nowadays also for data

- well-specified delays

- echo problems

PSTN

ISDN

PCM

IP, Frame-relay

ATM

X.25

ATM

Frame-relay

IP, UDP*

*User Datagram Protocol


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Transmission & Switching: Transmission in Telephone Network

Analog / Digital

PABX

SW

SW

SW

SW

SW

PABX

SW

SW

Satellite


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Optical Transmission

Optical Fiber or Microwave Link

Digital

switch

Digital

switch

HighTDM

HighTDM

Low

TDM

Low

TDM

TDM

Packet

IWF

TDM

Packet

IWF

TDM Frames

Packets with Gap

Native Packets Native Packets


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Low Time Division Multiplexing (TDM)

Unique bit pattern to

delimit frames

1 0 0 1

0 1 0 1

1 0 0 10 1 0 1

Low

TDM

XX

1 Frame


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Thank You !

Documents

Transmission and Switching PDF