Test Papers / Previous Question Papers of IGNOU CS09 Data Communications and Networking June 2005

ADCA / MCA (II Yr)
Term-End Examination

June, 2005

CS09 : Data Communications and Networking

Time: 3 hours
Maximum Marks: 75

1. (a) How has the PCM sampling time been set at 125 μ sec ? Explain the process. (5)

(b) A processo n Host t has been assigned port P, and a process on Host 2 has been assigned port Q. ls it possible for there to be two or more TCP connections between these two ports at the same time ? Explain. (4)

(c) Consider a half duplex point-to-point link using the stop and wait scheme. What is the effect online utilization if
(i) the message size is increased so that fewer messages will be required?
(ii) the number of frames are increased for a constant message size ?
(iii) the frame size is increased ? (5)

(d) PPP is based closely on HDLC, which has user bit stuffing to prevent accidental flag-bytes within the payload from causing confusion. Give one reason why PPP uses character stuffing instead. Explain your choice of reason. (3)

(e) Differentiate between ARP and RARP with an example of each. (4)

(f) Give two reasons, and explain, why network might use an error-correcting code instead of error detection and retransmission. (5)

(g) Why is CSMA/CD not applicable to a wireless environment ? (4)

2. (a) What is the reason for using an encoding scheme in FDDI that is different from the one used in CSMA/CD ? Explain the FDDI token ring operation, with an example. (10)

(b) Why does ATM use small, fixed length cells ? (5)

3. (a) Consider the Internet congestion control algorithm.
(i) Explain all ihe parameters used in the algorithm. (3)
(ii) Plot the congestion window as a function of the transmission number, and explain the function of the algorithm. (7)

(b) What is a subnet ? How do you implement subnetting? Explain this with an example. (5)

4. (a) Why is compression required ? Compare the JPEG and MPEG formats, with explanation. (5)

(b) Write the shortest path routing algorithm, and explain each stage. (10)

5. (a) Explain the following in the context of transport layer : (7)
(i) Addressing scheme
(ii) Flow control and Buffering schemes

(b) A channel has a bit rate of 4 kbs and a propagation delay of 40 m sec. For what range of frames does stop-and-wait give an efficiency of at least 60 percent ? (8)