DipIETE – ET (OLD SCHEME)

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:                                 (2 10)

a. The lowest level network in the data network is:

(A)  Metropolitan area network       

(B)  Local area network

(C)  Wide area network        

(D)  Wi-Fi network

b. POTS stands for

(A)  Public operated Telephone System                                                                           

                   (B)  Post Office Telegraph System

(C) Plain old telephone system           

(D)  Packet operation telephone system

             c.   In a strowger exchange subscriber is generally connected to:

(A) Two motion selector                     (B) Uniselector

(C)  Line relay                                     (D) Multiselector

             d.   Common control requires:

(A)  A separate channel                      (B)  The data channel

(C)  Both voice and data channel         (D)  None of the above

             e.   The 8 bit PCM VF channel requires a frame of:

(A) 2 microsec                                   (B)  64 microsec

(C)  20 microsec                                 (D)  125 microsec

             f.    The time taken for the two phase operation is given by:

(A)  Ts = Nt_d + N (t_d+t_c) (B)  Ts = t_d + N (t_d+t_c)

(C)  Ts = Nt_d + Nt_c (D)  Ts = Nt_d + (t_d+t_c)

             g.    In DTMF touch tone pad, the combination of frequencies 1209 Hz and 770 Hz is used to transmit digit:

(A)  0 (B)  2

(C)  1                                                  (D)  4

             h.    In a non blocking network the cross points should be

(A)  (n–1)N (B)  n(N–1)

(C)  nN                                               (D)  n(N+1)

             i.    MAC address is used for

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

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

             j.    ISO/OSI reference model for computer network is

(A)  Five layered model                       (B) Seven layered model

(C)  nine layered model                        (D) consists of tables

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Classify switching systems and explain the importance of trunking.                       (8)

             b.   Explain the importance of Grade of service and Blocking Probability. Over a 20 minute observation interval, 60 subscribers make calls. Total duration of calls is 5000 seconds. Calculate the load offered to the network by the subscribers and the average subscriber traffic.                                         (8)

Q.3     a.   What is input controlled time division space switch, explain how this enhances the Performance.                                                                 (8)

             b.   List out and explain the function of various basic circuits used for selector control in switching stages.                                                                       (8)

Q.4     a.   Draw the schematic and explain the working of a DTMF instrument.                   (8)

b.   Explain how 30 voice frequency channels are transmitted using a 125 microsecond PCM frame.                 (8)

Q.5     a.   Draw n-stage time and space combination switching system and show how blocking can be reduced by this design concept.                                    (8)

     b.   Design a three stage network for 100 incoming and 200 outgoing trunks indicate the configuration and number of cross points required. Draw the configuration.                                                    (8)

  Q.6     a. How SPC helps in enhanced services, explain with examples.                             (8)

             b.   What does grade of service and blocking probability signify in a switching network and how are these taken care of.                                                (8)

Q.7     a.   What are the effects of delay, explain how delays are taken care of in telephone Networks.                                                                       (8)

b.   What is the advantage of common channel signalling, how this is implemented. Draw the signalling message format for Single Unit Message (SUM).                                                                             (8)

Q.8     a.   What are the major differences between voice and data traffic. Explain briefly the switching techniques used for data transmission.                           (8)

             b.   Explain the importance of Presentation layer in data communication.                    (8)

Q.9           Write short notes on any TWO of following:                                        (8  2 = 16)

                   (i)   State transition diagram.

                   (ii)  Concentrators.

                   (iii) Subscriber loop system.