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Friday, 12 June 2015

Computer and Communication Networks -Model question paper for B.E/B.Tech Engineering



1(a) Explain two types of Packet-Switched Networks. (6 Marks)
(b) Suppose that virtual paths are set up between every pair of nodes in an ATM network. Explain why connection setup can be greatly simplified in this case. (4 Marks)
(c) Find the average clipping time for each burst of information in statistical TDMs. (6 Marks)
(d) Consider a time division multiplexer having a frame time of 26 μs. Each user channel has 6 bits, and each frame has 10 bits of overhead information. Assume that the transmission line carries 2 Mb/s of information. How many user channels can be accommodated on the line? (4 Marks)
2(a) Write a note on orthogonal frequency division multiplexing. (8 Marks)
(b) For a local area network using CSMA/CD, assume a 12 percent frame error rate owing to noise and errors resulting from collisions. Discuss how the throughput U could be affected. (8 Marks)
(c) Consider a 2 Mb/s satellite transmission link through which 800-bit frames are transmitted. The propagation time is 200 ms. Find the link efficiency, using the stop-and-wait protocol. (4 Marks)
3(a) Mention some applications of Mesh networks. (4 Marks)
(b) What is Congestion? Explain the method to perform Congestion control at network layer. (6 Marks)
(c)  Distinguish between flood routing and deflection routing. (4 Marks)
(d) Consider a cellular network with 128 cells and a cell radius r=3km. Let g be 420 traffic channels for a N=7-channel cluster system. Find the area of each hexagonal cell, total channel capacity and the distance between the centers of nearest neighbouring cochannel cells. (6 Marks)
4(a) What are the two most important forms of transportation in the TCP/IP network? Explain. (8 Marks)
(b) Find out about an IP address that is well known to you, such as that of your college or your work server. Set up an experiment in which you look up the domain name for this IP address. (6 Marks)
(c) Write a computer program to find the cipher text for a message, using DES to encrypt a 64-bit message, including all 0s with a 56-bit secret key consisting of 1010…10. Assume that a 1-bit rotation in the key process. (6 Marks)
5(a) Explain Non-Markovian and Self-Similar models of queueing systems. (6 Marks)
(b) In a nonpreemptive priority queueing scheme, a low-priority flow is guaranteed to receive 10% of the total bit rate s of the transmission link. How much better does this low-priority flow perform? What would be the impact on the performance of the high-priority flows? (4 Marks)
(c) What are the three types of blocking switch fabrics? (6 Marks)
(d) Compare the complexity of large-scale three-stage and five-stage clos switching systems, where the number of ports varies from 1000 to 2000 ports. (4 Marks)
6(a) Write a note on classification of optical switch elements. (4 Marks)
(b) To design an 8 x 8 optical router, we are comparing three different structures, each using, respectively, a crossbar switching network, a Spanke-Benes network, and an 8 x 8 directional coupler. Which structure offers the best overall cross-talk suppression? Which structure has the lowest overall average switching delay? (6 Marks)
(c) What is multicast backbone? Explain. (4 Marks)
(d) To optimize the routing delay in a sparse-mode PIM, find the optimal place for the rendezvous point. Give an example of a spanning tree, and justify your answer. (6 Marks)
7(a) What are virtual private networks? Explain the two types. (6 Marks)
(b) Consider an overlay network that consists of five connected nodes. Compare two methods for a peer-to-peer connection on top of the internet using a ring topology. (8 Marks)
(c) Assume that a normal-distributed source with zero mean and variance of 2 is to be transmitted via a channel that can provide a transmission capacity of 4 bits/each source output. What is the minimum mean-squared error achievable? What is the required transmission capacity per source output if the maximum tolerable distortion is 0.05? (6 Marks)
8(a) Write a note on Self-Similarity with Batch Arrival Models. (6 Marks)
(b) Compare table-driven and source-initiated routing algorithms in terms of (a) Speed of routing table updates and (b) Point-to-point routing when there is a sudden change in the network topology. (8 Marks)
(c) What are the three main blocks of the sensor node? Explain. (6 Marks)

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