Test Papers / Previous Question Papers of IGNOU CS09 Data Communications and Networking December 1996

ADCA / MCA (II Yr)
Term-End Examination

December, 1996

CS09 : Data Communications and Networking

Time: 3 hours
Maximum Marks: 75

1 (i) What is the difference between band width, baud rateand channel capacity? [5]

(ii) What is the difference between a confirmed service and unconfirmed service? For each of the following tell whether it might be a confirmed service and unconfirmed service, both or neither: [5]
· Connection establishment
· Data transmission
· Connection release

(iii) Why is a virtual terminal protocol needed? What kinds of applications are likely to use it? [2]

(iv) Sketch the Manchester encoding for the bit stream: 0001110101 [2]

(v) A group of N user stations share a 56 Kbps pure Aloha Channel. Each station outputs a 1000 bit frame on an average of once every 100 sec (stations are buffered). What is the max value of N? [5] (vi) If the bit string 0111101111101111110 is subjected to bit stuffing, what is the output string? [2]

(vii) X .21 does not provide for multiplexing at layer 3. Why? [4]

(viii) With reference to ISO reference model, point out which layer/layers carry the following functions: [5]

· Text/data compression
· Virtual terminal management
· Connection management
· Error free data transmission · Deadlock control

2 Explain the operations of CSMA/CD Bus and token passing bus. Compare advantages and disadvantages of each. Why is the latter favoured for real time application such as process control? [15]

3 (i) Explain the following ISO Terms: [6]
· Service data unit
· Interface data unit
· Protocol data unit

(ii) Describe a situation in which protocol data unit is different in size from interface data unit and service data unit. [6]

(iii) What are the different service primitives in the OSI model for connection oriented service? [3]

4 (i) Describe main message errors which typically occur at the data link layers. Explain how such errors occur and a method of correction. [7]

(ii) Compare the two data link protocols: Go back N and Selective Repeat in terms of flow control, error recovery and packet loss. [8]

5 (i) TCP uses a single transport header whereas OSI has many of them? Discuss the advantages and disadvantages of each method. [7]

(ii) Discuss the differences between OSI Class 4 and TCP. [8]

6 (i) With respect to point to point WAN, distinguish the following: [8]

* Virtual circuit service and datagram service.
* Adaptive routing and nonadaptive routing
(ii) What is deadlock in point to point subnet? How is deadlock prevented in such subnet? [7]