Chap 5 Telecom Switching [Compatibility Mode] - Copy.pdf

7/27/2019 Chap 5 Telecom Switching [Compatibility Mode] - Copy.pdf

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TELECOM SWITCHING

MODULE 1

BY:- GAURAV KUMAR


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Chapter 03

Topics to be covered in this session :-

History of Telephone Exchange Types Of Switching

Redundancy Methods

Session Objective:-

BY:- GAURAV KUMAR

g a w c ng


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SWITCH

In a telecommunications network, a switch is a device

that channels incoming data from any of multiple inputports to the specific output port that will take the datatoward its intended destination.

BY:- GAURAV KUMAR

The process of channelizing the data to the correct inletsand outlets is termed as switching.

It plays an important role in the telecommunication

field as this is the main unit which takes the datafrom one end of the user terminal to the other userend.


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History

First automatic exchange (Electro mechanical) appeared in 1892.

Strowger Exchanges: disadvantages, large number of mechanicalparts, limited availability, inflexibility, bulky in size etc.

Crossbar Exchanges (1926): improved many short- comings of

BY:- GAURAV KUMAR

Strowger system by many common equipments like Register,Marker, Translator etc.

Electronic Exchanges: a large number of moving parts werereplaced en-block by a single computer. Smaller in size, faster and

reliable, highly flexible, noise-free, easily manageable with nopreventive maintenance etc.


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Redundancy Methods

Load Sharing

BY:- GAURAV KUMAR

N+1 Redundancy


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Load Sharing

In load-sharing, each processor has access to all inputs

and outputs. Calls are randomly distributed for processing to either oftwo processors.

Two processors share the resources dynamically, but

BY:- GAURAV KUMAR

. An inter-processor link exchange information for mutual

coordination and for hardware or software exclusionmechanism to prevent both processors accessing the sameperipheral device.


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Load Sharing

Telephone Environment

BY:- GAURAV KUMAR

A B

MA MB

Ex


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Hot Stand By

Provide redundancy in a single processor operation.

Active processor handles total traffic and other onstandby.

Standby is totally decoupled from active both in HW &

BY:- GAURAV KUMAR

.

Standby will be in place on-line only if active fails.

When active processor failed, it is incapable of doing anyoperation.

To avoid this problem, processor must have acommon memory.


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Hot Stand By


BY:- GAURAV KUMAR

A B

Common Memory

an y


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N+1 Redundancy

Multiprocessor systems have the N+1 system

configuration One processor is added as a redundant unit.

This unit can, under normal conditions, take part of thetraffic handling

BY:- GAURAV KUMAR

N+1 configuration has a larger capacity than theengineered value

In case of failure of any processor, the redundantprocessor takes up the entire load of the failed

processor.


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N+1 Redundancy


BY:- GAURAV KUMAR

P1 P2 Pn P n+1

M

M1 M2 Mn M n+1


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Types Of Switching

BY:- GAURAV KUMAR


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Circuit Switching

CS network establishes a fixed circuit between exchangesand terminals before the users may communicate

Exchanges were physically connected with an electricalcircuit.

Delay is constant during the connection.

BY:- GAURAV KUMAR

released

In CS, a route is reserved from source to destination. CS, relatively inefficient because capacity is wasted on

connections, which are set up but are not incontinuous use. Connection is immediately available and capacity is

guarantee until the call is disconnected.


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Circuit Switching

BY:- GAURAV KUMAR


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Packet Switching

PS splits traffic data into packets that are routed over a shared

network. PS is the process of segmenting a message/data to betransmitted into several smaller packets.

Each packet is labeled with its destination and the number of

BY:- GAURAV KUMAR

t e pac et to e p t e pac et n ts est nat on. Each is dispatched and many may go via different routes. At the destination, the original message is reassembled in the

correct order, based on the packet number.

PS networks do not require a circuit to beestablished and allow many pairs of nodes tocommunicate almost simultaneously over thesame channel.


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Digital Switching

Digital switching system carries several time division

multiplexed (PCM) samples. Samples are conveyed on PCM highways.

Switching environment requires placing digital samples

BY:- GAURAV KUMAR

TS of another PCM

Types Of Digital Switching:-Space Division SwitchingTime Division SwitchingHybrid Division Switching


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Space Division Switching

In space-switching mode, corresponding time-slots of I/C

and O/G PCM highways are interconnected.I/P O/P

HW 1

TS 6

BY:- GAURAV KUMAR

Space DivisionSwitch

HW 2HW 3

HW 4

HW 5

Highway Changer


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Time Division Switching

Time Switching involves interconnection of different time

slots on the incoming and outgoing highways by re-assigning the channel sequence.

HW 1

BY:- GAURAV KUMAR

Time DivisionSwitch

HW 2

HW 3

HW 4HW 5

Time slot Changer


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Digital Time Switching

Speech or Buffer memory(SM)

Digital Time Switch Memories

BY:- GAURAV KUMAR

time-slots arrive

Control or Connection or Address Memory

(CM)Controls writing and reading of samples in

Buffer memory


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Time Switch Operating Modes

Output associated controlSamples of I/C PCM are written in SM sequentially andindependent of CM while reading is controlled by CM,

BY:- GAURAV KUMAR

Input associated control

Samples of I/C PCM are written in a controlled way, i.e.,in the order specified by CM and read sequentially.


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Output Associated Control

TS 4

I/C PCM TS1TS2

TS 3

TS 4

O/G PCM

TS 6

Speech sample

BY:- GAURAV KUMAR

TS 31

Speech memory

Four

TS 6Time slotcounter

Control memory


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Input Associated Control

Speech sampleTS 4 TS 6

I/C PCM O/G PCMTS1

TS2

TS 6

BY:- GAURAV KUMAR

Time slotcounter

Six

TS 31

TS 4

Speech memory

Control memory


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Limitations by the use single Space or Time Switch

Space Switch, become complex as the switch sizeincreases.

Memory location requirements go up as a Time Switch isexpanded, making it uneconomical.

It is economical to employ number of stages, using small

BY:- GAURAV KUMAR

switches to build a large network. This result in necessity of changing both TS and HWY in

large networks.


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Hybrid Switching

TS 6

TS 14

HW 1HW 2

HW 3

BY:- GAURAV KUMAR

SwitchHW 4

HW 5


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Two Dimension Network

Network employing both Space and Time switches is

known as Two Dimensional network.

BY:- GAURAV KUMAR


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REVIEW

In this session we discussed about the:-

History of Telephone Exchange Types Of Switching

Redundancy Methods

BY:- GAURAV KUMAR

Digital Switching


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Documents

Chap 5 Telecom Switching [Compatibility Mode] - Copy.pdf