AMIETE – ET/IT (OLD SCHEME)

Code: AE17 / AT17                                          Subject: TELECOMMUNICATION 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       Choose the correct or the best alternative in the following:                                  (210)

a.  The traffic in a telecommunication network is measured by an

internationally accepted unit known as  

(A)  Erlang.                                         (B)  Hertz.

                    (C) Decibel.                                       (D)  None of the above.                                       

b.   Step by step switching system is a

(A) direct control system.                    (B)  indirect control system.

(C)  hybrid control system.                   (D)  None.

             c.   The process of first compressing and then expanding is referred to as  

(A) encoding.                                     (B) modulation.

(C) companding.                                  (D) None of the above.

             d.   Delay systems are sometimes known as      

(A) first line theory.                              (B)  second line theory.

(C) waiting line theory.                        (D) None of the above.

             e.   Loss formula is also called as

(A) Erlang A formula.                        (B)  Erlang B formula.

(C)   Erlang C formula.                        (D)  Erlang D formula.

             f.    A combined modulator/demodulator unit is called

(A) CODEC.                                     (B) EPABX.

(C)  MODEM.                                    (D) None.

g.   PSTN stands for  

(A) Public Switched Telephone Network.

(B) Private System Transmission Network.

(C)  Private Subscriber Telephone Network.        

(D)  Public Switched Transmission Network.

             h.   The type of hand-off found in CDMA system is

(A) hard hand-off.                               (B)  medium hand-off.

(C) soft hand-off.                                 (D)  None.

             i.    Decryption and encryption of data are the responsibility of ________ layer.    

(A)  Physical                                        (B)  Data link

(C) Presentation                                  (D) Session

             j.    The bandwidth of an optical fiber is

(A)  1300-1550 nm.                            (B)  1300-1550 .

(C)  1300-1550 mm.                           (D)  None.

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   What do you understand by a switching system?  Classify different switching systems and explain each one of them, briefly.                                        (10)

             b.   Explain the 2-wire and 4-wire transmission system.                                             (6)

Q.3     a.   Explain different switching network configurations in detail.                                (10)

b.   Explain the concept Echoes and Singing.                                                             (6)

Q.4     a.   Discuss the following with reference to telecommunication traffic.

(i)   Traffic characterization.

                   (ii)  Loss systems.

                   (iii) Delay systems.                                                                                           (10)

b.    Determine the implementation complexity of a 2048-channel STS switch implemented for 16 TDM links with 128 channels on each link. The desired maximum blocking probability is 0.002 for channel occupancies of 0.1.                                                                                                                   (6)

Q.5     a. What are the basic advantages of a cellular architecture in mobile telephony?                         (5)

     b.   Explain the structure of a GSM channel.                                                             (5)

     c.   What do you understand by the term CDMA?  Draw and explain the architecture of a CDMA system.                                                                  (6)

  Q.6     a. Explain different elements of optical fiber transmission system.                             (8)

             b.   Write a short note on line codes used in optic transmission.                                 (6)

             c.   Determine the difference in wavelength of two optical signals separated by 2 GHz and centered at 1500 nm.                                                                                                                         (2)

Q.7     a.   What are the factors responsible for the developments towards ISDN?               (4)

b.   Draw the architecture of ISDN network and explain.                                          (6)

             c.   Explain briefly the different schemes of signalling used in ISDN systems.              (6)

Q.8           Write short note on the following:

(i) Circuit switching.

(ii)  ISO-OSI reference model

                   (iii) LAN, MAN and WAN.

                   (iv) ATM networks                                                                             (4  4 = 16)

Q.9     a.   Describe the advantages and disadvantages of optic fibre used as a transmission medium.  Also describe its various applications.                             (8)

b. A subscriber makes three phone calls of three minutes, four minutes and two minutes duration in a one hour period.  Calculate the subscriber traffic in Erlangs, CCS and CM.                                       (6)

c. Explain VPCs and VCCs supported by ATM.                                                   (2)