TELCOM2310_MT_Fall2009_Solutions - University of Pittsburgh...

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TELCOM 2310 ± Midterm Exam ± Fall 2009 Page 1 of 5 University of Pittsburgh Name: …………………………………. TELCOM 2310: Computer Networks Midterm Exam ± Fall 2009 Solutions Part 1. True/False questions (1 pts each) 1. A lost TCP acknowledgement does not necessarily force a retransmission T 2. HFC (Hybrid Fiber-Coaxial) transmission rate is shared among users T 3. Getting an object from a Web cache may take more time than getting it from its source T 4. ICMP is reliable because ICMP packets are carried in TCP segments F 5. Consider a TCP connection C over IP between a host A and a host B. All packets of C will follow the same path (i.e., same sequence of routers) to host B F Consider a TCP connection between a host A and a host B. Host A sends a packet P that is fragmented into m fragments. 6. Either all m fragments of P will reach host B or none will F 7. The number of times a packet is fragmented depends on the route it takes to reach host B T 8. If a packet P and its fragments are fragmented several times, then host B will receive packet P as a set of several fragments of equal sizes F 9. Let C be a TCP connection between host A (sender) and host B (receiver) and let x be the current value of the base of its window (i.e., send_base) at time t . At time t , there may be, at most, one ACK segment still in transit from B to A that has a sequence number lower than x . F 10. The receiver of a UDP segment computes the Internet checksum for the received segment and compares it to the value carried in the checksum field. If the receiver finds that k ( k > 0) bits are different, then it can conclude that, at least, k bits are incorrect F 11. The initial phase of a TCP connection is called slow start because the sender’s transmission rate increases slowly by 1 MSS every RTT F 12. In general, TCP Reno achieves better throughput than TCP Tahoe T 13. If a router uses longest prefix matching, then the number of entries in its forwarding table cannot exceed the number of its interfaces F 14. Let R1 and R2 be two routers connected through a direct link L. If R1 always fragments packets sent to R2, then R2 alsways fragments packets sent to R1 F 15. A router has m input ports and n output ports. If n > 2. m , then there will never be any packet queued at one of the input ports F Part 2. Give short answers (1-2 lines) to the following questions (2 pts each)
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This note was uploaded on 12/11/2009 for the course TELECOM 2310 taught by Professor Rezgui during the Fall '09 term at Pittsburgh.

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TELCOM2310_MT_Fall2009_Solutions - University of Pittsburgh...

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