CompNetMidtermFall09

CompNetMidtermFall09 - EPFL-logo Midterm - Computer...

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EPFL-logo Midterm - Computer Networks Prof. J.-P. Hubaux and Dr. M. H. Manshaei November 3, 2009 Duration: 1:45 hours, closed book. Please write your answers on these sheets, at the end of each question; use extra sheets if necessary (put your name on them). You may write your answers in English or in French. The total number of points is 40. This document contains 19 pages. Student First name: Last name: Division: 2 Communication Systems 2 Computer Science 2 Other (mention it): . . . . . . . . . Year: 2 Bachelor Year 2 2 Bachelor Year 3 2 Other (mention it): . . . . . . . . . (answers to the questions are shown in italic and blue)
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1 Short questions (5 points) For each question, please circle a single best answer . 1. What advantage does a circuit-switched network have over a packet-switched network? (a) It can support wireless connections. (b) It can be implemented over fiber-optic link. (c) It can provide the same services with less overhead. (d) It can guarantee a certain amount of end-to-end bandwidth. CORRECT (e) All of the above. 2. A tier-1 ISP: (a) is connected to all other tier-1 ISPs. CORRECT (b) is connected to only a few of tier-1 ISPs. (c) is a customer of one or more tier-2 ISPs. (d) Both (a) and (c) 3. What information is used by a process running on one host to identify a process running on another host? (a) The data rate between the source and the destination in bits/sec. (b) IP address of the destination host. (c) Port number of the destination socket. (d) Both (b) and (c). CORRECT (e) All of the above. 4. FTP sends control information out of band . This means that: (a) FTP usually uses more bandwidth than HTTP or SMTP. (b) FTP uses two UDP connections simultaneously. (c) FTP uses two TCP connections simultaneously. CORRECT (d) Both (a) and (b). (e) Both (a) and (c). 2
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5. Suppose that you want to do a transaction from a remote host to a server as fast as possible. Which transport protocol would you use? (a) FTP. (b) HTTP. (c) UDP. CORRECT (d) TCP. 6. With the Selective Repeat protocol: (a) the receiver sends individual ACK packets. CORRECT (b) the sender has a timer for the oldest unacked packet. (c) the receiver sends cumulative ACK packets. (d) Both (a) and (b). 7. Which parameter is used to calculate the timeout interval in TCP? (a) Sample Round Trip Time (RTT). (b) RTT variation. (c) Average congestion window size. (d) Both (a) and (b). CORRECT 8. After a loss event detected by triple duplicate ACK, TCP Reno (a) cuts its congestion window to 1 Maximum Segment Size (MSS). (b) goes to fast recovery phase. CORRECT (c) goes to slow-start phase. (d) Both (a) and (c). 9. Consider a server socket object: socket = ServerSocket(12345); What does the invocation of socket.accept() return? (a) true if there is a new TCP segment in the socket’s buffer; false otherwise. (b) A new TCP segment from the socket’s buffer (blocks if no segments are available). (c) true if a new TCP connection request has arrived; false otherwise (d) A socket associated with a new TCP connection (blocks if no connections are available).
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This note was uploaded on 01/09/2012 for the course CS cs464 at Bilkent University.

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CompNetMidtermFall09 - EPFL-logo Midterm - Computer...

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