Code: C-12 / T-10                                  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 best alternative in the following:                                         (2x10)

a. What is the main function of transport layer?

(A)  Node-to-Node delivery               

                   (B)  Synchronization

(C)  Process-to-Process delivery        

(D) Updating and maintenance of routing tables

b. Communication between a computer and a keyboard involves _________ transmission.

(A) Simplex                                        (B)  Half-Duplex

(C)  Full-Duplex                                  (D)  Automatic

             c.   If the data unit is 111111 and the divisor 1010, and the remainder 110, what is the dividend at the receiver?

(A) 111111011                                  (B)  111111110

(C)  1010110                                      (D)  1101111111

             d.   Which type of switching uses the entire capacity of a dedicated link?

(A)  Circuit switching                         

(B)  Datagram packet switching

(C)  Virtual circuit packet switching          

(D)  Message switching                      

             e.   In Go-Back-N ARQ, if frames 4,5 and 6 are received successfully, the receiver may send an ACK _____________ to the sender.

(A) 5                                                  (B)  6

(C)  7                                                  (D)  Any of A, B, C

             f.    An ARP reply is _________ to _______.

(A) Broadcast; all hosts                      (B)  Multicast; one host

(C)  Unicast; all hosts                           (D)  Unicast; one host

             g.   The access method for wireless LANs as defined by IEEE802.11 is based on __________.

(A) CSMA                                        (B)  CSMA/CD

(C)  CSMA/CA                                  (D)  Token passing

             h.   Dijkstra’s algorithm is used to ______________

(A) Create LSAs                                (B) Flood an Internet with Information

(C) Calculate the routing tables            (D) Create a link state database

             i.    The IP header size is __________

(A) 20 to 60 bytes long                       (B) 60 bytes long

(C) 20 bytes long                                 (D) Depends on the MTU

             j.    In an ATM network, all cells belonging to a single message follow the same __________ and remain in their original order until they reach their destination.

(A)  Transmission path                         (B)  Virtual path

(C)  Virtual circuit                                (D)  None of A, B, C

Answer any FIVE Questions out of EIGHT Questions.

Each question carries 16 marks.

Q.2     a.   Differentiate between

(i) Services and Protocols

(ii) Connection oriented and Connectionless service.                    (6+4)

             b.   What signal-to-noise ratio is needed to put a T-1 carrier on a 50 kHz line?          (6)

Q.3     a.   An  picture is scanned by a scanner having a resolution of  pixels per square inch.  How many bits are produced if the scanner uses 8 bits/pixel?  How many bits are required if each pixel uses 256 colours?                                                                                                     (6)

             b.   What are polynomial codes?  Explain the various steps involved in generating CRC code with an example.                                                           (10)

Q.4     a.   What is multiplexing?  Explain the T-1 carrier system and the hierarchy in T-series.             (10)

b.   Discuss SS7 network architecture with suitable diagrams.                                   (6)

Q.5     a.   Explain Go-Back-N ARQ protocol with a diagram.  Derive an expression for utilization efficiency. How it overcomes the inefficiency of stop-and-wait ARQ protocol?                                              (12)

     b.   Write the frame format of HDLC and explain the need for bit stuffing with an example.                    (4)

  Q.6     a. Differentiate between ARP and RARP.                                                              (8)

             b.   In an Ethernet LAN, only working speed has been increased from 10 Mbps to 100 Mbps.  Find the minimum length of data field.                (8)

Q.7     a.   Discuss datagram and virtual circuit packet switching with suitable examples.                      (5+5)

b.   Consider the network shown.

Use the shortest path algorithm to obtain

(i) The shortest path from node 2 to node 6.

(ii) The shortest path from node 2 to node 6 when the link between node 2 and node 4 goes down.                                               (6)

Q.8     a.   How are IP addresses assigned when using CIDR?  Explain with an example.                     (5+5)

             b.   Discuss the real time Transport protocol.                                                            (6)

Q.9     a.   Describe the header format of an ATM cell.                                                       (8)

b.   Explain UNI signalling with a suitable diagram.                                                    (8)