The Institution of Engineers,India 2006 Diploma Electronics and Communication ELECTRONIC SWITCHING SYSTEMS - - Question Paper

Code: D-20  Subject: ELECTRONIC SWITCHING SYSTEMS

Time: 3 Hours                                                       June 2006                                              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       Choose the correct or best alternative in the following:                                         (2x10)

a.       Side tone is the speech heard by 

                   (A)  the receiving subscriber

                   (B)  both the receiving and calling subscriber

(C)   by on looker

(D)  by calling subscriber

b.      Busy hour traffic is the

                   (A)  maximum average simultaneous traffic.

                   (B)  traffic during peak hour.

(C)     traffic when all subscribers are engaged.

(D)    the duration of maximum calls.

             c.   The final selector is connected to the 

(A)    calling subscriber.                         (B) switching network.

(C) called subscriber.                           (D) line finder.

             d.   In a DTMF phone a dialling of 8 generates

(A)    1336 Hz- 770 Hz                        (B)  1209 Hz - 1477 Hz

(C)  1209 Hz- 941 Hz                        (D)  1336 Hz-852 Hz       

             e.   SPC stands

(A)     Standard Protocol Control           (B)  Stored Program Control

(C)  Signaling and switching Centre      (D)  Signaling Process Center

             f.    For two stage network the switching elements for M inlets with r blocks and N outlets with s blocks is given by

(A) Ms + Nr                                       (B)  Mr + Ns

(C) (M + N) (r + s)                             (D)  (M + N)rs

             g.   As per Nyquist criterion the sampling rate is

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

(C) (1/2fs)                                           (D) (2/fs)

Where fs is the signal frequency

             h.   Common channel signalling in SS7 is

(A) outband control channel.                (B) inband control channel.

(C) speech control channel.                  (D) none of the above.

             i.    Broad Band ISDN handles data rate of about

(A)   64 kbps                                        (B) 100 mbps

(C) 5.4 mbps                                       (D) 2.048 mbps

             j.    MAC address helps in

(A)  multimedia access control.            (B)  media access control.

(C)  mobile access control.                  (D) master access point control.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

  Q.2     a.   In a hundred-line exchange 24 two-motion selectors are used. Draw the schematic you suggest for this exchange and explain its working. How many simultaneous calls can be made during peak hour in this exchange?                                           (10)

             b.   Compare electromechanical switching system with electronic switching system.                   (6)

  Q.3     a.   What is centralised SPC, what are its modes of operation, explain the working of any one of these?                                                                       (8)

             b.   Explain the architecture of SS7 and compare with seven-layer OSI architecture.                 (8)       

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

             b.   Show how finite state machine model helps in designing a switching system and give a typical example.                                                                   (8)

  Q.5     a.   Through two block diagrams explain the difference between Space division and time division switching.                                                            (8)

             b.   Define congestion and grade of service. In a particular exchange during busy hour 1200 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 and

(iv)              period of congestion                                                                   (8)

  Q.6     a.   Distinguish between single stage and multistage networks.                                 (10)

             b.   In a two stage network there are 512 inlets and outlets, r=s=24. If the probability that a given inlet is active is 0.8, calculate:                                     

(i)                  The switching elements

(ii)                Switching capacity

(iii)               Blocking probability                                                                   (6)

  Q.7     a.   Explain the CCITT hierarchical structure of switching and routing using block schematic.                 (8)

             b.   In a subscriber loop that contains a series resistance of 300 ohms to protect the batteries in the exchange, a normalized telephone draws 10 mA and  its standard input d.c. resistance is 50 ohms. Calculate the maximum distance at which a subscriber can get good speech reproduction if a cable of 52 ohms/km resistance is used. If a standard hand set of 30 mA current is used what will be the change.             (8)

  Q.8     a.   What are the advantages of CCS over in-channel signalling.                                (8)

             b.   Show how the signalling has progressed from SSI to SS7.                                  (8)

  Q.9     a.   What is the need of MODEM in data communication. Explain at least one modulation technique used for high speed modems.                            (10)                                                                      

             b.   What are the advantages and disadvantages of packet switching over circuit switching.                    (6)