Telecom Transmission & Switching System Engr.Asaf khan
Email:
[email protected]
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COURSE OBJECTIVE To familiarize with different types of switching
systems
To have a understanding of various types signaling systems To have a knowledge of traffic engineering and concepts
To have a concept about Various Transmission Systems
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READINGS Class Notes/Discussions
Books Telecommunications Switching, Traffic & Networks J.E. Flood Data Communication and Networking, 4th Edition Behrouz A. Forouzan Data and computer Communication , 7th Edition William Stalling !
Signaling in Telecommunication Network John G.van Bose
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COURSE OUTLINE Introduction (Chapter1 J.E Flood) Evolution of Switching systems (Chapter 8 B.A Foruzan) Signaling in PSTN (John G.van Bose) ISDN (William Stalling) Next Generation Network SIGTRAN ATM and Signaling in ATM
Optical Fiber network-SDH (Siemens CBTs+Notes) DWDM networks (Misc) GPON (Misc) & Miscellaneous Topics 4
GRADING POLICY Assignments
5%
Quizzes
15%
First Sessional
15%
Second Sessional
15%
Final Exam
50%
Grading Policy is tentative 5
RULES & REGULATIONS You are expected to take active part during lectures You are strongly discouraged to enter the lecture room after the class has already begun You are strongly advised to attend lectures
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Overview ! !
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Introduction to telecommunication Early Telephone network Switching Transmission Media Signaling Standards
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INTRODUCTION TO TELECOM A telecommunications network can be considered as a system of the following interacting subsystems Switching Systems Transmission Systems
Signaling Systems
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EARLY TELEPHONE NETWORK Stringing a wire between every pairs of telephones that might want to communicate was not good Long Term Policy
A better idea was to connect all the telephones to a central switching office. There an operator could connect one telephone to another via a switch board
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SWITCHING OFFICE In this telephone system, each telephone user could connect to any other telephone in the town by a cranking handle This would ring a bell in the switching office to attract the attention of the operator The operator talked to the telephone user to enquire to whom they wished to be connected to. She then manually connected the caller to the calle using a jumper cable on a plug board to physically connect the telephone wires
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SWITCHING EXCHANGE
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EVOLUTION OF TRUNK EXCHANGES It was soon apparent that the callers did not just want to talk to the people in the same town but also to the peoples in the neighboring town To connect every telephone in a number of towns to a single switching office was impractical .The wires were too long and the operator would have been overloaded
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TRUNKS The answer was to have switching offices
Using this two-tier hierarchy It was possible to connect a caller to the switching office that could connect them in turn to the switching office in the destination town Automatic switching offices enables switching in a fraction of a second
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PUBLIC SWITCHED TELEPHONE NETWORK Soon Customer wanted to talk to different regions , states and other countries. To cope with this, even more tiers were added to the hierarchy.
To make a call we now dial a number. This number is examined by the local exchange, which decides if it can connect with local telephone exchange or if it needs to connect you via a higher level of hierarchy
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PSTN EXCHANGES HIERARCHY
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LOCAL EXCHANGE Provides POTs, PRIs, BRIs Serves the subscribers Features for subscribers
Either subscribers on both the ends or subscribers on one end and switch on other end Gets the clock from Tandem
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TANDEM EXCHANGE Provide POTS, PRIs, BRIs A center point for local exchanges More PRIs links
Subscribers Features Gets the clock from transit Can be connected to : Local Tandem Transit 17
TRANSIT EXCHANGE No provision of POTs Connection to Transit on one end and Tandem on other end Lots of PRI links
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TANDEM-TRANSIT EXCHANGE Serves same as local tandem No provision of POTS
Connected both ends to Transit Gets the clock from international gateway
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INTERNATIONAL GATEWAY EXCHANGE No provision of POTS Connected to Transit on one end and International
Gateway on other end Source of Clock
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CLASSIFICATION OF SWITCHES Class 1 exchanges are international gateways - handing off and receiving traffic from outside country or national networks. Class 2 exchanges are tandem exchanges which interconnected whole regions of the national network. Class 3 exchanges are tandem exchanges connecting major population centers within particular region of the national network. Class 4 exchanges are tandem exchanges connecting the various areas of a city or towns in a region.
Class 5 exchanges are the exchanges to which end-users telephone lines would connect.
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TRANSMISSION MEDIA In traditional analogue telephone systems the telephone is connected to the local exchange via Cat 3 UTP cables This connection is called local loop. It is typically between 1Km and 10 Km in length. Higher up in the hierarchy, higher bandwidth cables are used to carry multiple telephone calls. Specifically digital lines on fiber is used Analogue systems used a technique called Frequency Division multiplexing (FDM) is used to do so
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SIGNALING In telephony context ,signaling means the passing of info and instructions from one point to another relevant to setting up and supervision of a telephone call By Tradition signaling has been divided into two types Subscriber Signaling Trunk signaling
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SIGNALING The trunk Signaling has further been divided into Channel Associated signaling Common Channel Signaling Channel Associated Signaling (CAS) i.e. Signaling in the speech channel (in-band ) Common Channel Signaling (CCS) i.e signaling in a channel that is totally separated from the speech channels and where the signaling channel is common for a large number of speech channels
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TERMINOLOGIES
British System
North American System Customer’s loop Central office end office Inter-office trunk Junctor Toll office Trunk network
Local/Access Network Exchange Local Exchange Junction Trunk Trunk Exchange Trunk network
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STANDARDS ITU-T ( former Consultative committee of telephone and telegraph) : It studies technical questions, operating methods, tariffs and data communications. ITU-R ( former Consultative committee of international radio communication) : p2p communications, mobile services and broadcasting
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OSI REFERENCE MODEL Physical layer : defines interface of connections, voltage level and data rate (connectors, signal form, modulation) Link layer : error detection and correction (point to point communication) Network layer : establish connection b/w nodes (End to end connectivity) Transport layer : establish connection b/w hops (End to end reliable transfer and flow control) Session layer : setting up and maintaining a session (begin, end, suspend sessions, integrate connections) Presentation layer : concerned with the format of the data (Represent information, compression, encryption) Application layer : defines nature of the task to be performed. For example e-mail, word processing. (service to the end users 27
SUMMARY
Local loop connects subscriber to the local exchange Trunk connects different exchanges
In PSTN Local loop is analogue and trunk is digital employing digital multiplexing techniques e.g. TDM and WDM SS7 is a common channel signaling protocol 28
RECOMMENDED READING Chapter 1 : Introduction Telecommunications Switching, Traffic and networks by
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J.E Flood
