chap 5 telecom switching [compatibility mode] - copy.pdf
TRANSCRIPT
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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
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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
Telephone Environment
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
Telephone Environment
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
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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
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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
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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
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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
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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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