Test Papers / Previous Question Papers of IGNOU CS09 Data Communications and Networking December 2006

ADCA / MCA (II Yr)
Term-End Examination

December, 2005

CS09 (S): Data Communications and Networking

Time: 3 hours
Maximum Marks: 75

1. (a) How does fragmentation process of IPv6 differ from IPv4? (2)

(b) A router has just received the following new IP addresses 57.6.96.0/21, 57. 6.I04.0/21, 57. 6.112.0/21 and 57.6.120.0/21.If all of them use the same outgoing line, can they be aggregated? If so, to what? If not, why? Explain with reason. (6)

(c) Is it necessary that every autonomous system use the same intra-AS routing algorithm? Why or why not? Explain. (3)

(d) Consider a subnet with 720 routers. How many entries will be required at each router if there is no hierarchy? If the subnet is partitioned into 24 regions of 30 routers each, how many local and remote entries will be required at each router? (5)

(e) Generate a CRC code for the data word 110101010 using the data word 10101. If the code word is received as 1100100101011, check if there are errors in the code word. (5)

(f) Suppose there is a heavy traffic on both a CSMA/CD LAN and on a Token Ring LAN. A station on which system is more likely to wait longer to send a frame? Why? (3)

(g) List and explain the two basic types of ISDN services.Describe channel capacity in B-channel and D-channel and its applications. (6)

2. (a)List the advantages of QAM over PSK. Draw the constellation diagram for the following: (6)
(i) ASK with amplitude levels of 1 and 3 units. Also calculate the baud rate if the bit rate is 4800 bps.
(ii) 4-PSK. Also calculate the baud rate if the bit rate is 6400 bps.

(b) What is the purpose of 'Hamming Code'? How are the redundant bits computed fgt a data unit of m-bits? Find the Hamming Code for the data unit 1001101 . (5)

(c) Show the operation of a Sliding Window protocol with the help of a diagram. Also explain the concept of pipelining and piggybacking. (4)

3. (a) A large population of ALOHA users manages to generate 50 requests/sec., including both originals and retransmissions. Time is slotted in units of 40 msec. (7)
(i) What is the chance of success on the first attempt?
(ii) What is the probability of exactly K collisions and then a success?
(iii) What is the expected number of transmission attempts needed?

(b) Describe the following three fields of Ip header: (3)
(i) Fragmentation offset
(ii) Time to live
(iii) Service type

(c) A bit stream 1100101011 is transmitted using standard CRC method. The generator polynomial is x³+1. Show the actual bit transmitted. Suppose the third bit from left is inverted during transmission. Show how this error will be detected. (5)

4. (a) What is the purpose of cladding in an optical fiber? Discuss its density relative to the core. (3)

(b) State the criteria used to evaluate transmission media. (3)

(c) Write shortest path routing algorithm using Dijkstra's algorithm. (9)

5. (a)Differentiate between upward multiplexing and downward multiplexing. (2)

(b) A new virtual circuit is being set up in an ATM network. Three ATM switches lie between the source and destination hosts. How many messages will be sent to establish the circuit? (3)

(c) What is the major disadvantage in using NRZ encoding technique? How do RZ encoding and biphase encoding attempt to solve the problem? (4)

(d) List and explain the problems encountered by a bridge in forwarding a packet from one LAN to another LAN. (6)