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8/14/2019 Telecommunication Switching system Control of Switching system.pdf
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UDHAY PRAKASH P
Uday3prakash @gmail.com
10/15/2012TSSN 4ECE JNTUHCEH1
Control of switching system
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Call processing functions
10/15/2012TSSN 4ECE JNTUHCEH3
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
10/15/2012TSSN 4ECE JNTUHCEH4
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
10/15/2012TSSN 4ECE JNTUHCEH5
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Handshake signal exchange diagram for
a local call
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10/15/2012TSSN 4ECE JNTUHCEH7
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
10/15/2012TSSN 4ECE JNTUHCEH13
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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10/15/2012TSSN 4ECE JNTUHCEH18
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