AMIETE – ET (NEW SCHEME)   –   Code: AE64

 

Subject: TELECOMMUNICATION SWITCHING SYSTEMS

Flowchart: Alternate Process: DECEMBER 2009Time: 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       Choose the correct or the best alternative in the following:                                  (210)

       

             a.  In a switching network connection between an incoming trunk and an outgoing trunk is called as _____________

       

                  (A) Outgoing call connection                 (B) Transit call connection

                  (C) Incoming call connection                 (D) Local call connection

 

             b. Step by step switching system employs a ______________ control system.

       

                  (A) Indirect control system                   

                  (B) No control system

                  (C) Direct control system                     

                  (D) Both direct and indirect control systems.

 

             c.  A cross bar switching system of size nm, employs _____________ number

                  electromagnets to select one of the nm sets of contacts.

                 

                                                                              (A) n electromagnets             (B) m electromagnets

                  (C) (n + m) electromagnets                   (D) (n  m) electromagnets

 

             d.  In a lost call system, full availability means every call that arrives can be connected to ______________

 

                  (A) First outgoing trunk which is free    

                  (B) Last outgoing trunk which is free

                  (C) Any outgoing trunk which is free    

                  (D) All outgoing trunks which are free

 

             e.  If the two stage switching network has N incoming trunks and N outgoing trunks, then the total number of cross points  is given by __________

 

                  (A)                                                 (B)

                  (C)                                            (D)


             f.   In designing a grading to provide access to ‘N’ outgoing trunks from switches having availability K, the number of graded- groups ‘g’ required is given by

                  ________________

                  (A)  g = NK                                         (B) g =

                   (C) g =                                        (D) g =

       

             g. In time division switches, with 8 KHz sampling rate, a sample occurs at every                                              ____________ microseconds.

 

                  (A) 100                                                (B) 125

                  (C) 256                                                (D) 64

 

             h.  In a simple telephone call ,call request or seize signal is a ____________

 

                  (A) Backward signal                             (B) Forward signal

                  (C) Forward and backward signal         (D) Status signal

       

             i.   Message switching enables circuits to attain an occupancy approaching __________ during the busy hour.

 

                  (A) 0.25 Erlang                                    (B) 0.50 Erlang

                  (C) 0.75 Erlang                                    (D) 1.0 Erlang

 

             j.   In narrow band ISDN networks, the data is transmitted at  _____________

 

                  (A) 1.5 Mbits/sec                                 (B) 2 Mbits/sec

                  (C) 64 Kbits/sec                                   (D) 2.4 Kbits/sec

 

 

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

 

 

  Q.2     a.   Briefly explain the functions of a switching system.                                               (4)

 

             b.   Briefly explain the principle of crossbar switching system                                     (5)

        

         c.  Draw and explain the trunking diagram of a 1000 line strowger exchange.            (7)

 

  Q.3    a.   Derive an expression for probability of x calls in progress,  P(x) =  P(0) and hence obtain an expression for Erlangs-Lost call formula for an exchange having N full availability trunks. Briefly explain the assumptions made in obtaining this expression.                                                                     (11)

 

b.   During the busy hour, on average 30E is offered to a group of trunks. On average the total period during which all trunks are busy is 12 seconds, and two calls are lost. Find the average number of calls carried by the group and the average call duration.  Show that the average number of calls offered to the group during a period equal to the average call duration is 30.                                                    (5)

       

Q.4            a. What is meant by the grading? Briefly explain skipping and homogeneous gradings.                      (7)

                                                             

             b.   Determine the total number of cross points for a two stage concentrator with M-incoming and N-outgoing trunks (given M>N).                            (3)

       

       .     c.  Design a three stage network for connecting 100 incoming trunks to 500 outgoing trunks.                 (6)

            

Q.5      a.  Explain time multiplexed time switching and compare it with time multiplexed space switching.                     (10)

 

             b.   An STS network has 10 incoming highways, 10 outgoing highways and 10 time switch links. The highways convey 32 PCM time slots. The average occupancy of incoming PCM channels is 0.7E.

                   (i)    Derive an equivalent space division network.

                   (ii)   Estimate the blocking probability.

                   (iii) Estimate the grade of service when an incoming call must be connected to a selected outgoing highway but may use any free channel on it.       (6)

 

  Q.6     a.   Explain the signals exchanged for a local call with the help of timing diagram.                                   (8)

 

             b.   Describe the architecture of the centralized SPC with its modes of operation for dual-processor architecture.                                                                                                                         (8)          

  Q.7     a.   With relevant sketches explain 30-channel PCM signalling scheme.                     (8)

 

             b.   Explain in detail the CCITT signalling system number 7 (CCITT  SS7).                                           (8)

  Q.8     a.   Explain the packet switching.  Compare it with circuit switching and message switching.                  (6)

 

             b.   List the features of ATM and explain the basic functions of ATM switch.           (10)

            

  Q.9     a.   Explain the need and architecture of intelligent networks.                                     (8)

 

             b.   What is ISDN? Sketch the ISDN user access reference configuration and explain each block.                                                                   (8)