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VTU Electronics and Communication Engineering (Semester 8)
Digital Switching Systems
December 2014
Total marks: --
Total time: --
INSTRUCTIONS
(1) Assume appropriate data and state your reasons
(2) Marks are given to the right of every question
(3) Draw neat diagrams wherever necessary

1 (a) Explain briefly the network structures used in telecommunication network.
10 M
1 (b) With neat diagram, explain the hierarchy used in the national Public Switched Telephone Network (PSTN).
6 M
1 (c) With neat diagram of elementary time-division multiplexing system, explain the principle of time-division mutiplex transmission.
4 M

2 (a) Briefly explain the functions of a switching system.
8 M
2 (b) With the neat block-diagram of subscribers line interface circuit, mention the functions implemented by it.
4 M
2 (c) With neat block-diagram explain the different functions performed by stored program control switching system.
8 M

3 (a) Define traffic intensity, holding time, congestion, grade of service and occupancy.
5 M
3 (b) Derive the expression for Grade of Service (GOS) of a lost-call system having N trunks, when the offered traffic is A Erlangs.
10 M
3 (c) 10 E of traffic is offered to switches that hunt sequentially over a group of trunks. Estimate the traffic carried by each of the first three trunks.
5 M

5 M
4 (b) Design a grading for connecting 20 trunks to switches having 10 outlets. Find the best grading. Represent the different possible gradings using grading diagram.
10 M
4 (c) Design a three stage network for 100 incoming and 100 outgoing trunks.
5 M

5 (a) With a neat diagram, briefly explain the space switch K incoming and m-outgoing PCM highways.
6 M
5 (b) With neat diagram explain time-space-time switching (T-S-T) network.
6 M
5 (c) With neat diagram explain the frame-alignment of PCM signals entering a digital exchange.
8 M

6 (a) With a neat diagram, explain the classification of digital switch software.
10 M
6 (b) Write a short note on a basic call model.
10 M

7 (a) Write a short note on the interface of typical digital switching system central office.
10 M
7 (b) Write a short note on strategy for improving software quality.
10 M

8 (a) Write a short note on digital switching system hardware architecture.
10 M
8 (b) Write a short note on digital switching system software architecture.
10 M

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