June 1999

Question Paper of CS-09 – Data Communication & Network of June 1999 from IGNOU

1 Consider a half-duplex point to point link using a stop and wait scheme.

(i) What is the effect on line utilization of increasing the message size so that fewer messages will be required? Other factors remain constant.

(ii) What is the effect on line utilization of increasing the number of frames for a constant message size?

(iii) What is the effect on line utilization of increasing frame size?

(iv) In the following figure, frames are generated at node A and sent to node C through B. Determine the minimum transmission rate required between B and C so that the buffers of node B are not flooded, base don the following:

� The data rate between A and B is 100 Kbps.
� The propagation delay is 10 m sec/mile for both sides.
� Full duplex lines between nodes.
� All data frames are 1000 bits long; track frames are separate frames of negligible length.
� Between A and B, a sliding-window protocol with a window size of 3 is used.
� Between B and C, stop and wait is used.
� No errors.

(v) Using Dijkstra�s algorithm, generate a least-cost route to all other nodes for nodes A to K. Do the same for Bellman-Ford algorithm.

(vi) Could HDLC be used as a data link control proto col for a LAN? If not, what is missing?

2 Discuss in detail about the physical description, applications and transmission characteristics of the following:
(i) Coaxial Cable
( ii) Microwave
(iii) Satellite
(iv) Broadcast Radio

3 (a) How does digital transmission work? How does DM (deta modulation) improve the performance of PCM (Pulse Code modulation)?

(b) Discuss the characteristics of T1 carrier.

(c) Why should PCM be preferable to DM for encoding analog signals that represent digital data.

4 Discuss the following in context of FDDI MAC protocol:
(a) List two key differences between FDDI and IEEE 802.5
(b) Illustrate graphically the operation of FDDI token ring.
(c) FDDI frame formats description
(d) Priority scheme

5 Answer the following questions related to IP (Internet Protocol):

� Describe a way to do reassembly of IP fragments at the destination.

� The protocol field used in the IPV4 header is not present in the fixed IPV6 header. Why not?

� Describe IP address formats.

6 Compare the following through examples.
� Transparent bridge and source routing bridge.
� Two-way handshake and three-way handshake.
� Credit allocation flow control and sliding window flow control mechanism.
� Upward multiplexing and downward multiplexing.

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