Computer Networks - 2004 2005 Exam - Electrical Engineering, Exams of Electrical Engineering

Download Computer Networks - 2004 2005 Exam - Electrical Engineering and more Exams Electrical Engineering in PDF only on Docsity! THE MANCHESTER METROPOLITAN UNIVERSITY FACULTY OF SCIENCE AND ENGINEERING DEPARTMENT OF ENGINEERING AND TECHNOLOGY SESSION 2004/2005 Examination for the BSc (HONS) INFORMATION TECHNOLOGY BSc (HONS) COMPUTER NETWORK TECHNOLOGY BSc (HONS) MEDIA TECHNOLOGY FINAL YEAR UNIT 64EE3038 : COMPUTER NETWORKS Tuesday 17 May 2005 2:00 pm to 5:00 pm Instructions to Candidates Answer FIVE questions. Students are permitted to use their own calculators, subject to Faculty conditions. S110 24/01/2005 1 1. (a) The ISO Reference Model is a framework for coordinating the development of OSI standards. Outline the abstractions used within the Reference Model and explain what it means for the network to be compatible with the Reference Model. Indicate whether two ISO compatible network products are guaranteed to work with one another. [8] (b) The ISO Reference Model uses connection-oriented communication and connectionless communication. Explain what is meant by these terms and discuss the characteristics of connection-oriented and connectionless communications. [12] S110 24/01/2005 Continued 4 4. (a) Discuss the video-on-demand (VOD) service, identifying the problems that would be associated with its implementation and the solution to these problems. Use the example of a 90 minute film to illustrate the difficulties that could occur with a strict implementation and the benefits of the solution. [5] (b) Explain what is meant by the terms bit interleaving and word interleaving and discuss their use in the plesiochronous digital hierarchy (PDH) and synchronous digital hierarchy (SDH). [5] (c) Explain how the synchronous digital hierarchy (SDH) overcomes the limitations of the plesiochronous digital hierarchy (PDH) and show the structure of the SDH. [5] (d) Figure Q4 shows the structure of a SDH synchronous transport module at level 1 (STM –1). Signals such as a single speech channel and a video signal (from a VOD type service) can be accommodated within a synchronous transport module. By use of appropriate shading, show how a single speech channel and a 4.096 Mbit/s video channel can be accommodated within the synchronous transport module using Figure Q4, which is also available as a separate sheet and should be included with your answer. [5] 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 9 9 (a)Frame alignment 270 columns9 columns of frame overheads SDH frame structure (STM-1). (a) Outline frame structure. (b) Frame structure in rows and columns 125 µs (b) Figure Q4 S110 24/01/2005 Continued 5 5. (a) Explain the purpose of congestion control as used in the transmission control protocol (TCP). [4] (b) Consider the effect of using slow start on a channel with a 10ms round-trip time and no congestion. Find the time that it takes before the first full window can be sent if the receive window is 24kB and the maximum segment size is 2kB. [4] (c) If a TCP congestion window is set to 18kB and a timeout occurs, calculate the window size if the next four transmission bursts are all successful. It may be assumed that the maximum segment size is 1kB. [4] (d) If the TCP round-trip time, RTT, is currently 30ms and acknowledgements arrive after 26, 32 and 24ms, respectively, find the new RTT estimate using the Jacobson algorithm if α = 0.9. [4] (e) Discuss the need for a persistence timer in the Transport Control Protocol. [4] 6. (a) Explain the meaning of the term deadlock and how it occurs in computer networks. [6] (b) Show and describe the relationship that throughput and network delay have with network loading for a routed computer network. [4] (c) Discuss the effects that routing and flow control have on the delay versus throughput characteristics of a routed computer network. [5] (d) Outline the flow control techniques available in such networks. [5] S110 24/01/2005 Continued 6 7. (a) List the services which can be envisaged via a broadband ISDN network. [6] (b) An ATM network operates with a transmission rate of 155Mbit/s and a propagation delay of 5µs per km. Determine the packetization delay for: (i) an 8-bit speech encoder transmitting at 64kbit/s; (ii) an 8-bit video encoder transmitting at 2Mbit/s. [4] (c) A telephone connection using the above network is 1000km in length. It passes through five switching centres, each introducing a maximum delay of 1ms. Find the maximum delay encountered by the speech signals. [5] (d) If the number of information bits per cell is trebled to improve the throughput of the network, discuss the effect which this has on telephone transmission. [5] S110 24/01/2005 Continued