Code: DE20                                                     Subject: ELECTRONIC SWITCHING SYSTEMS

Time: 3 Hours                                                                                                     Max. Marks: 100

NOTE: There are 9 Questions in all.

· Question 1 is compulsory and carries 20 marks. Answer to Q. 1. must be written in the space provided for it in the answer book supplied and nowhere else.

· Out of the remaining EIGHT Questions answer any FIVE Questions. Each question carries 16 marks.

· Any required data not explicitly given, may be suitably assumed and stated.

Q.1 A    Choose the correct or the best alternative in the following:                                   (2x10)

a. Engaged tone is generated in the:

(A)  Telephone instrument of calling subscriber      

(B)  Telephone instrument of called subscriber

(C)  Exchange   

(D)  Repeater

b. One Erlang is equal to

(A)  3600 CCS                                  

                   (B)  36 CCS

(C) 60 CCS                                      

(D)  24 CCS

             c.   The analog signal needs to be sampled at a minimum sampling rate of:

(A) 2fs                                               (B) 1/(2fs)

(C)  fs/2                                              (D) 2/fs

             d.   In a time division space switch the size of the control memory is N and its Width:

(A) (B)

(C) (D)

                   where N are the outlets and M the number of data samples

             e.   In a single stage network:

(A) There is no redundancy               

(B)  There is redundancy

(C)  Alternative crosspoints are available   

(D)  Alternative paths are available

             f.    Signaling transfer point (STP) exist in

(A)  Strowger exchange                       (B)  SS7

(C)  Local area network                      (D)  PABX

             g.    ARQ is transmitted in the event of:

(A)  Loss of signal                               (B)  Error in received data

(C)  Improve reliability                         (D)  During time out

             h.    Computer to computer communication is:

(A)  Simplex                                        (B)  Duplex

(C)  Half Duplex                                  (D)  Both Duplex and Half Duplex

             i.    A distributed network configuration in which all data/information pass through a central computer is

(A) Bus network                                 (B) Star network

(C)  Ring network                                (D) Point to point network

             j.    An important terminal that is required between DTE and PSTN is

(A)  Server                                          (B) MODEM

(C)  Relay                                           (D) Network card

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Describe the nature of signals produced on the subscriber’s loop by a pulse dialer, and a touch tone dialer.                                                            (8)

             b.   Draw a 100 line exchange using two motion selectors and explain, how switching takes place in it.              (8)

Q.3     a.   List the major difference in Single Stage, Two Stage and Three Stage Networks. Also discuss their blocking characteristics.                                     (8)

             b.   How time slot interchange switch works in time multiplexed time switching, explain using schematic.                                                                         (8)

Q.4     a.   What are different control function categories, explain how they help in signalling and control.                                                                     (8)

b.   Explain the following:                                                                                         (8)

                   (i) Busy Hour                                       (ii)  Peak Busy Hour

                   (iii) Time consistent Busy Hour             (iv) Traffic intensity

Q.5     a.   Explain the principles of operation of centralized SPC and distributed SPC and compare their performance.                                                                                                                         (8)

     b.   Draw the schematic of a CCS and explain, giving its advantages.                         (8)

Q.6     a. What is the difference between message switching and packet switching, explain typical packet switching network configuration.                         (8)

             b.   Explain CSMA/CD and CSMA/CA protocols used in LAN’s, discuss its advantages and limitations.                                                                    (8)

Q.7     a.   Describe the architecture of SS7 common channel signaling network with the help of a neat labeled diagram.                                                                                                                         (8)

b.   Define congestion and grade of service. In a particular exchange during busy hour 900 calls were offered to a group of trunks, during this time 6 calls were lost. The average call duration being 3 minutes. Calculate:

                   (i) Traffic offered in erlangs                  (ii) Traffic lost

                   (iii) Grade of service                            (iv) Period of congestion                        (8)

Q.8     a.   Explain how presentation layer helps in establishing and processing data in End to End layers.                                                                    (8)

             b.   Explain the need of network and channel graphs in designing a multistage network giving examples.                                                            (8)

Q.9           Write short notes on:                                                                                      (4x4)

                   (i)  DTMF

                   (ii) Numbering plan

                   (iii) OSI layer

                   (iv) Topologies used in networking