B.E./B.Tech. DEGREE EXAMINATION, MAY/JUNE 2007.
Electronics and Communication Engineering
EC 054 – TELECOMMUNICATION SWITCHING AND NETWORKS
Time: Three hours
PART A — (10 x 2= 20 marks)
1. What is the inherent error present in PCM system? Why does it occur?
2. Why are electronic switching systems _called as stored program control systems?
3. Can circuit switching be employed for data traffic?
4. How many four-wire voice circuit connections can be provided by a
bi directional PAM switching bus if the minimum achievable pulse width is 250 nsec?
5. “Exponential call holding times represent a random process” Justify.
6. Distinguish channel associated signaling from common channel signaling.
7. Why the structure of a cell is hexagonal?
8. What is the capacity of T1-carrier system? How is this rate arrived?
9. What is a WAN?
10. What are the advantages of CDMA?
PART B — (5 x 16 = 80 marks)
11. (a) (i) What is a fully connected network? Illustrate with an example. How many links are required to fully interconnect 50 subscribers? (4) (ii) What is a side tone? Is it necessary or not necessary? With the help
A of circuit diagram describe the working of side tone coupling circuit. (8) (iii) What is aliasing? Why does it occur? How is it avoided in a PCM system? (4)
(b) (i) Design a 100 line stronger switching system (by any one method).(8) I (ii) With the help of a diagram corresponding to multi exchange network, describe how common control system over comes the basic difficulties faced by a stronger system. (8)
12. (a) (i) Prove that the total number of cross points Nx required by a three N 2 stage switch is Nx = 2Nk +kn
Where N = number of inlets — outlets, n = size of each inlet- outlet group, k = Number of centre stage arrays. (6)
(ii) Determine the implementation complexity of the TS switch where
A the number of TDM input lines N: 80. Assume each input line
P contains a single DS1 signal (24 channels). Assume that a single stage matrix has been used for the space stage. (6)
(iii) What is TSI? Explain its working using a suitable diagram. (4)
(b) (i) What is combination switching? Why is it employed? (4)
(ii) what is message switching? Is it employed commonly nowadays? Why? (4)
(iii) With a suitable diagram, explain the operation of random input/random output time switch. (8)
13. (a) (i) Describe SS7 protocol architecture. (10)
(ii) A switching system serves 10000 subscribers with a traffic intensity of 0.1 E per subscriber. If there is a sudden spurt in the traffic
increasing the average traffic by 50%, what is the effect on the arrival rate? (3)
(iii) What is the probability that a 1000-bit data block experiences exactly four errors while being transmitted over a transmission link with a BER of 10•5? (3)
(b) (i) Compare loss systems and delay systems. (4)
(ii) Over a 20 minute observation interval, 40 subscribers initiate calls. Total duration of the calls in 4800 seconds. Calculate the load
offered to the network by the subscribers and the average subscriber traffic. (4)
(iii) How are Birth-Death processes used to model the steady state behavior of a telecommunication switching system? With the help of appropriate equations, prove the point. (8)
14. (a) (i) Describe the layered architecture of SONET/SDH transmission scheme. (10)
(ii) Describe BORSCHT(6)
(b) (i) “The performance requirements of ISDN are much greater than conventional networks”. Why? (4)
(ii) Distinguish between synchronous and asynchronous multiplexing. Which one is preferred and when? (4)
(iii) Describe with appropriate diagrams, the salient features of cellular mobile communication.(8)
3 A 1186
15. (a) (i) Describe TCP/IP protocol architecture. Compare and contrast it with ISO-OSI
(ii) Compare CSMA protocol with CSMA/CD protocol. i (4) (iii) ls ATM a connection oriented protocol? Why? . (2)
(b) (i) What is packet switching? List out its merits and demerits. (4) (ii) Describe the functioning of the internet. (8)
(iii) Why is the cell in ATM protocol chosen as 53 bytes long? What is the role of CLP bit in
ATM cell? (4)