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VTU Electronics and Communication Engineering (Semester 8)
Digital Switching Systems
December 2013
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) What is the need for subdividing an exchange area? Explain the impact on network cost with number of exchanges.
4 M
1 (b) Explain the principle operation of frequency division multiplexing with neat diagram.
8 M
1 (c) Define gain in decibels and give their relation. An amplifier has input resistance of 600Ω and a resistive load of 75Ω. When it has an rms. input voltage of 100 mV, the RMS. output current is 20mA. Find the gain in dB.
8 M

2 (a) With a neat diagram, explain the basic operation of cross bar system.
4 M
2 (b) Explain the subscriber's line interface circuit for digital exchange.
6 M
2 (c) List all types of basic call processing techniques. Explain any two of them.
10 M

3 (a) Define the following: i) Erlang; ii) CCR; iii) Congestion; iv) Grade of service.
4 M
3 (b) Derive the expression for iterative form of Erlang's lost call formula.
10 M
3 (c) Four junctions are arranged in a full availability group. If the traffic offered to the group in busy hour is 0.8E Find: i) Grade of service and ii) Probability that only one trunk is busy.
6 M

4 (a) Differentiate between single and multistage networks.
5 M
4 (b) Briefly explain the principle of grading and list different types of grading.
5 M
4 (c) A grading is required to connect 30 out going trunks to switches of availability 10. Design a progressive grading.
10 M

5 (a) Explain the principle operation of S-T networks.
8 M
5 (b) What is frame alignment? Why is it required?
4 M
5 (c) A TST network has 20 incoming and 20 outgoing PCM highway, each conveys 30 channels. The required grade of service is 0.01 and 0.02. Find the traffic capacity of network in mode 1 and mode 2.
8 M

6 (a) Explain in brief three levels of software architecture.
10 M
6 (b) Explain software linkages during a call with a neat diagram. List three modes of operations of a features flow.
10 M

7 (a) Explain the strategy used for improvement of software quality.
14 M
7 (b) Explain the methodology for reporting and correcting the field problems with block diagram.
6 M

8 (a) With the aid of flowchart, discuss the basic steps necessary to complete a simple call.
8 M
8 (b) Explain common characteristics of digital switching system.
4 M
8 (c) Write short notes on: i) Reliability analysis: ii) Recovery strategy.
8 M

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