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

ADCA / MCA (II Yr)

Note: Question number 1 is compulsory. Answer any three questions from the rest.

1. (a) Under what conditions will satellite communication be prefened over fibre optics? (2)

(b) Sixteen bit messages are transmitted using Hamming Code. How many check bits are needed to ensure that the receiver can detect and correct single bit errors? Show the bit pattern transmitted for the message 1010110011001011. (4)

(c) Frames of 1500 bits are sent over 1 mbps channel using geostationary satellite whose propagation time from earth is 270 msec. Acknowledgements are always piggybacked onto data frames. Three bit sequence numbers are used. What is the maximum channel utilisation for Go-Back-n protocol? (5)

(d) Show the relationship between ASes, backbones and area routers in OSPF through a diagram and explain the operation of OSPF algorithms. (6)

(e) An organization is granted the IP address 130.34.12.64/26. The organization needs to have 4 subnets. What are the subnet addresses and the range of addresses for each subnet? (5)

(f) Distinguish between bit rate and baud rate. Give an example each, where both of them are same and different. (3)

(g) Calculate the maximum bit rate for a noiseless channel with a bandwidth of 3000 Hz, transmitting a signal with 4 signal levels. (5)

2. (a) Why does the maximum packet lifetime, T, have to be large enough to ensure that not only the packet but also its acknowledgement have reached? (2)

(b) A large token ring has 100 stations and token rotating time of 40 msec. The token holding time is 10 msec. What is the maximum achievable efliciency of the ring? (5)

(c) Explain the operation of Internet congestion algorithm through appropriate diagram. Also explain the purpose of the following parameters: (8)
(i) Congestion window
(ii) Slow start
(iii) Threshold

3. (a) Derive an expression for throughput of pure ALOHA and slotted ALOHA. Why is this value of throughput less for pure ALOHA and how is it improved in slotted ALOHA? (8)

(b) A stop and wait protocol uses a 100 kbps satellite link. It employs a round-trip propagation delay of 520 msec approximately. Find out the percentage of time the sender is blocked to wait for acknowledgement if the frame size is: (7)
(i) 1000 bits
(ii) 2000 bits
(iii) 10,000 bits

4. (a) Is it possible for an application to enjoy reliable data transfer even if the application runs over UDP rather than TCP? If so, how? (2)

(b) What is the relationship between the number of slots in a frame and the number of input lines for synchronous TDM? Repeat it for asynchronous TDM. (4)

(c) What is the primary difference between N-ISDN and B-ISDN? In B-ISDN, what is the difference between a distributive service and an interactive service? (5)

(d) what is count to infinity problem? Explain it through an example. (4)

5. (a) Why is Frame Relay unsuitable for real-time communication such as teleconferencing? (2)

(b) Draw the constellation diagrams for the following: (4)
(i) QAM-16
(ii) QAM-64

(c) You have a leaky bucket. What should be its capacity if the output rate is 5 gallons per minute, and there is an input burst of 100 gallons per minute for 12 seconds and there is no input for 48 seconds? (5)

(d) Define the following QoS parameters in the context of ATM with appropriate examples: (4)
(i) Constant bit rate
(ii) Real time variable bit rate
(iii) Non real time variable bit rate
(iv) Available bit rate