TELCOM2310_MT_Fall2008_Sols - University of Pittsburgh...

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TELCOM 2310 Midterm Exam Fall 2008 Page 1 of 7 University of Pittsburgh Name: Smart Studious Lucky TELCOM 2310: Computer Networks Midterm Exam Fall 2008 Grade: 105 / 105 Part 1. True/False questions (16 pts) 1. F The use of conditional GET in HTTP enables Web servers to periodically delete objects that have not been requested since a certain date. 2. T A single access to an object on a Web server may benefit simultaneously from DNS caching and Web caching. 3. F Unlike IMAP, POP3 enables users to create folders on mail servers. 4. F Consider two TCP connections: one (C1) between Host A (sender) and Host B (receiver), and another (C2) between Host C (sender) and Host D (receiver). If the senders A and C have identical congestion window sizes, then their throughputs are also identical. 5. F Let H1 and H2 be two Internet hosts. Host H1 executes the command Traceroute H2 and obtains the path: H1, R1, R2, .., Rn, H2. If host H2 executes the command Traceroute H1 at the same time H1 executes Traceroute H2 , then the path returned to H2 will necessarily be: H2, Rn, Rn-1, .., R2, R1, H1. 6. F TCP uses selective acknowledgements. 7. F In ATM networks, congestion control does not use direct network feedback. 8. T When tunneling is used to transmit an IPv6 packet, fragmentation is possible. 9. F ICMP is reliable. 10. F GBN (with a window size of N) works properly when the sequence number space (number of unique sequence numbers) is M such that M > N. 11. The timer’s expiration in GBN triggers the retransmission of: T at least one packet F at most one packet F exactly one packet T one or more packets 12. All F When the sender receives an ACK in SR, it advances its window by: at least one position at most one position exactly one position one or more positions 13. F 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 can be no ACK segment still in transit from B to A that has a sequence number lower than x . 14. T Consider a packet P sent from an IPv4 source A to an IPv4 destination B. Assume that one or more routers fragment the packet P while it is traveling to B into n fragments ( n 2). If any of the n fragments is lost (i.e., is not received at B), then the sender A will have to resend the packet P entirely. 15. F Consider a NAT-enabled router R that is (the only router) connected to a home network. Assume that the router runs a DHCP server that assigns IP addresses to computers within the home network. The router R must update its NAT translation table each time the DHCP server assigns a new IP address to a host on the network. 16. F The initial phase of a TCP connection is called slow start because the sender’s transmission rate increases slowly by 1 MSS every RTT.
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