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UDHAY PRAKASH P

Uday3prakash @gmail.com

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Control of switching system

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Call processing functions

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A similar set of basic sequence of operations must be

performed by any (circuit or packet) switching network.

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CALL PROCESSING::SEQUENCE OF OPERATIONS

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IDLE STATE

CALL REQUEST STATE

CALLING LINEIDENTIFICATION

DETERMINATION OFORIGINATING CLASS OF SERVICE

IDENTIFICATION OF CALLING PARTY

CONNECTION TO THE CALLINGPARTY

CONNECTION TO THE CALLING LINE

PROCEED TO SEND SIGNAL

ADDRESS SIGNAL

SELECTION OF OUTGOING LINETERMINAL

DETERMINATION OF TERMINATINGCLASS OF SERVICE

TESTING CALLED LINETERMINATION

STATUS SIGNAL

CONNECTION TO THE CALLEDLINE TERMINATION

ALERTING CALLED CUSTOMER

ANSWER SIGNAL

COMPLETION OFTHE CONNECTION

CONVERSATIONAL STATE

CLEAR SIGNAL

RELEASE OFCONNECTION

0

1

2

3

0

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Timing of signals exchanged for a local call

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Handshake signal exchange diagram for

a local call

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Channel associated signaling Common channel signaling

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State transition diagram

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State boxes Event boxes

Action boxes

Decision boxes Connectors

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Common control

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Performs specific callprocessing functions.

Used either or both in timedivision and space division

basis.

Present output depends onpresent and previous inputs.

Contention for commoncontrol line is resolved by

using a one-only selector orarbitor.

Crank-back principle.

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Example: System 12 Architecture

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Reliability, Availability and Security

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Availability +Unavailability =1

Availability=MTBF/(MTBF+MTTR)

Unavailability=MTTF/(MTBF+MTTR)

CCITT UNAVAILABILITY LIMITS FOR

TELEPHONE EXCHANGES

Entire system

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Security

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Not for attacks, but for reliability. Security measures used for

Line Circuits: None

Switching Network: None or partial duplicationCommon Controls: 1 in n sparing

Central Processors: Replication

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Stored Program Control

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Processor architecture Worker and standby mode

cold standby hot standby

Load sharing mode Synchronous mode---replication

Processor Failure

Hardware fault----recovery by reconfiguration

Software fault-----recovery by Roll-back

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Stored Program Control

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Distributed ProcessingProcessor cost reduction lead to decentralization of switching

system control to certain extend.

Regional Processor

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Stored Program Control

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Software

Each time a processor returns to a call, it needs to determine itsstate by reading:

Line Store

Call Record( time of origin, Equipment no. of line, Actions already taken, Switch

paths involved, Last signal received, Current call status, address digits received, timeof answer signal ,time to clear down)

Translation Tables

A map of the switching networks( mainly in map-in-memory technique)

COMPLETE EXCHANGE SOFTWARE =Application Software + Operating System

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Stored Program Control

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Software

OS provides the environment in which the application programsrun, whose functions include:

Timing Control

Scheduling

Interrupt Handling Interrupt Handling

Inter-processor Communication

Input/output Control

Storage Management

Human-Machine Communication

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Stored Program Control

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Central Processor functions(SOFTWARE IMPLEMENTED) Call Processing

Database Management

Fault diagnosis and alarm Processing Automatic Testing

Traffic recording

Changing customers facilities and directory numbers

Changing routings and routing codes

Generation of exchange management statistics

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Software for SPC is written in CCCITT High LevelLanguage(CHILL).

Then, software code is compiled into final object code, andstored processor program memory .

For some time critical applications, written in assemblerlanguage.

SOFTWARE BUILD

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Stored Program Control

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SPC exchange capacity is specified in terms of: Number of Lines

Traffic in Erlangs

Number of Busy Hour Call Attempts

Overloads are prevented by Overload control and Input Queue

ManagementMMI message transfer even during overload condition