Computer Networks — DU B.Sc. (Hons) Computer Science Previous Year Question Papers

Parts of a question must be attempted together. (g) A noiseless channel has bandwidth 4 kHz and uses 8 signal levels. A noisy 3 channel has the same bandwidth with SNR = 20 dB. Which channel has a higher maximum data rate? Justify. (h) A communication channel has a bandwidth of 10 Mbps between Device A and 3 (i) In Half-Duplex mode, A and B alternately transmit for 2 seconds each. Calculate the effective data rate experienced by each device over time. (ii) In Full-Duplex mode, both devices transmit simultaneously using the same 10 Mbps link. Explain how the bandwidth is utilized and determine the effective data rate for each device? (i) Modern computer networks rely on different devices operating at various layers 3 of the OSI model. Compare Hub, Switch and Router in terms of: (i) Layer of operation ) In a computer network, a host needs to send data to another host. It knows the 3 destination IP but not the MAC address. Write the name of the protocol and explain its working. 2 a) TCP is considered a reliable protocol, while UDP is called an unreliable and 7 connectionless protocol. Justify the above statement by comparing the mechanisms such as handshaking, error control, reliability, ordering of segments and congestion control. Provide examples of applications that benefit from each protocol. b) Answer the following questions with respect to the Stop and Wait Protocol: 8 (1) How does the Stop-and-Wait protocol handle duplicate frames? (ii) Why is a timer necessary at the sender side in the Stop-and-Wait protocol? What could happen if there's no timer? (iii) What is the significance of sequence numbers being only 1 bit in Stop-and-Wait ARQ? (iv) What happens if the sender sends a frame and the receiver receives it correctly, but the ACK frame is lost? Illustrate the complete flow with the help of a sequence diagram. a) Consider a network of six routers labelled A, B, C, D, E, and F. The cost of the 8 links between the routers is as follows: Using Dijkstra's algorithm, determine the shortest path from router A to router E and show all intermediate steps. Also, State the Optimality Principle. b) Discuss the advantages and disadvantages of allowing browsers to be extended using plug-ins and helper applications. Can a single-threaded web server handle multiple client requests at the same time? Justify your answer with reasons related to server architecture and performance. Describe the role of multithreading in improving Web server throughput. In a CSMA/CD network, a station experiences a collision after transmitting a frame. If this is the third collision, calculate the maximum wait time before the next transmission attempt. Assume a slot time of 50 us. What is the significance of the "backoff time" in CSMA/CD? An organization is assigned the IP address 192.168.10.0/24. The network 8 administrator needs to create two subnets to accommodate 120 and 30 hosts respectively. For each subnet: (i) Provide the subnet mask in dotted-decimal notation