Code: DE21/DC11                                 Subject: DATA COMMUNICATION & NETWORKS

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:                                   (2x10)

a. Which of the following performs modulation and demodulation?

(A) Fiber optic                                   (B)  Satellite

(C)  Coaxial cable                               (D)  Modem

b. The process of converting analog signals into digital signals so that they can be processed by a receiving computer is referred to as:

(A)  Modulation                                   (B)  Demodulation

(C) Synchronizing                               (D)  Asynchronizing

             c.   A required characteristic of an on-line real-time system is:

(A)  More than one CPU                    (B)  Offline batch processing

(C)  No delay in processing                 (D)  All the above

  d.   The systematic access of small computers in a distributed data processing system is referred to as:

(A)  Dialed service                               (B)  Multiplexing

(C)  Polling                                          (D)  Conversational mode

             e.   A teleprocessing system may consist of

(A) User systems                                (B)  Communications Systems

(C)  Computer center systems              (D)  All of the above

             f.     Computer network often work on the principle of

(A)  Remote switching                         (B)  Hybrid switching

(C)  Packet switching                           (D)  Message switching

             g.   In a __________ topology,  if there n devices in a network, each device has (n–1) ports to Band is always equivalent to

(A) Mesh                                           (B)  Star

(C)  Bus                                              (D)  Ring

h.   Communication circuits that transmit data in both directions but not at the same time are operating in:

(A) A Simplex mode                            (B) A Half-duplex mode

(C) A full-duplex mode                        (D) Asynchronous mode

             i.    An example of the medium-speed, switched communications services is:

(A)  Series 1000                                  (B) Data phone 50

(C) DDD                                             (D) All of the above

             j.    A Communications device that combines transmission form several I/O devices into online is a:

(A)  Concentrator                                (B) Modifier

(C)  Multiplexer                                   (D) Full-duplex line

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2       a.    What is Packet switching? Write the advantages and disadvantages of packet switch network. (8)

 b.    What are the different activities of Data link layer? (8)

Q.3     a.   State the principles that are applied to arrive at seven layers in OSI reference model.                      (6)

             b.   Television channel is 6 M Hz wide. How many bits per second can be sent if four level digital signals are used? (4)

c.   Discuss the various factors, affecting the performance of Network at the router level.          (6)

Q.4     a.   Write a short notes on ISDN and explain the advantages of it.                             (6)

b.   How does Errors Happen?  Give the name of the concerned network layer in which error control exists and explain the basic services of that layer.  (6)

             c.    A binary signal is sent over a 3000 Hz channel whose (S/N) = 10 dB.    

                                                                              What is the maximum achievable data rate? (4)

Q.5     a.   Illustrate different network topologies.  Explain one topology in detail, which is widely used in computer networking and comment as to why it is widely used.                                               (6)

     b.   State the design issues for the layers in Network Architecture.                             (6)

             c.   What is encoding and why it is needed in digital transmission? (4)

Q.6     a. What is the function of routing algorithm? Explain Link -Static routing. (7)

             b.   What are the functions of the ATM adaptation layer?  List the various ATM services.                     (5)

c.   What are X.25 protocol layer? How does each relate to the OSI layers? Name the frame types of X.25 and cite their primary functions.                                                                                (4)

Q.7     a.   What do you mean by TCP/IP?  Explain TCP segment format with a detailed diagram.                   (10)

             b.   Write short notes on Error Correction. (6)

Q.8     a.   Give a brief description of the application and discuss the advantages of the following types of transmission media:

(i) Twisted pair lines.

(ii) Microwaves.                                                                                            (10)

b.   Briefly explain the following with reference to application layer:

                   (i)   WWW

                   (ii)  HTTP

                   (iii) SNMP                                                                                                       (6)

Q.9     a.   Discuss the three main switching methods.  How is space division switching superior to time division switching.                                            (8)

             b.   Explain briefly the design issues of an application layer including FTAM, E-mail and virtual terminals.                                                                      (8)