CS118 Midterm 11F SOLUTION

CS118 Midterm 11F SOLUTION - CS 118 Computer Networking...

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CS 118 Computer Networking Fundamentals Midterm Exam Solution Fall 2011 Professor Mario Gerla 10/29/2011 Question Points Score 1 20 2 20 3 20 4 15 5 25 Total: 100 Name: _________________________ Student ID #: _____________________ Instructions: - Open book and Open notes - Open laptop without Internet connectivity - Calculators are also allowed
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Problem 1: True/False (2 points each, total 20 points) Determine if each of the following statements is true or false . Circle your answer. a) Sockets provide the interface between the transport layer and the network layer. TRUE FALSE b) FTP differs from HTTP in that it runs on two parallel TCP connections, and it maintains state information for each connected user. TRUE FALSE c) DNS can be used to support load distribution amongst several servers for a heavily visited website. TRUE FALSE d) Root Name Servers typically handle DNS queries iteratively, rather than recursively. TRUE FALSE e) The transport layer provides logical communication between two processes, while the network layer provides logical connections between two hosts. TRUE FALSE f) If a UDP checksum adds up to all 1’s at the receiver, we can be certain that the packet was not corrupted during transmission. TRUE FALSE g) Go-Back-N gives better performance than SR on noisy channels. TRUE FALSE h) In Go-Back-N, a receiver may slide its window as soon as it ACKs a packet that was received correctly and in order. TRUE FALSE i) TCP uses cumulative ACKs, and the ACK number is the number of the last correctly received byte. TRUE FALSE j) TCP’s congestion control mechanism responds differently to a timeout event and a 3- duplicate-ACK event. TRUE FALSE
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Problem 2: Short Answer (20 points) Answer the following questions. Be brief and concise. a) (8) Consider two TCP connections sharing the same link. The connections have very different round trip propagation delays (eg, one is a local connection, with RTT = 5 ms; the other goes over a satellite link, with RTT = 500 ms). Both TCP
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CS118 Midterm 11F SOLUTION - CS 118 Computer Networking...

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