SampleMidterm1sol - CS 118 Fall 2002 Sample Midterm#1...

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CS 118 – Fall 2002 Sample Midterm #1 Solutions You may use a single 8 ½ x 11 sheet of paper, front and back, with any notes you like. You may also use a calculator. 1. (7) True or False: (a) Error control for reliable transfer is implemented only at the link layer. FALSE – Implemented at many layers (b) In a circuit switched network, after setting up an end-to-end circuit, the transfer time of a file is deterministic, not random. TRUE – no congestion occurs in circuit switched networks (c) UDP is an unreliable datagram protocol because it does not check packets for errors upon arrival, whereas TCP does verify the checksum on incoming packets. FALSE – UDP does calculate checksums and check for corrupt packets (d) Reliable data transfer can not be achieved if an unreliable transport protocol such as UDP is used. FALSE – RDT may be implemented at the application layer (e) Congestion control is not needed over circuit switched networks. TRUE – no congestion since circuits are reserved (f) The number of entries in the root DNS servers grows linearly with the number of end- systems (hosts) using the Internet. FALSE – The DNS database is stored hierarchically, so not every host has an entry at the RNS’s. (g) Sockets provide the interface between the transport layer and the network layer. FALSE – Sockets provide the interface between the Application Layer and the Transport Layer 2. (3) For each of the following scenarios, indicate (with an X in the appropriate column) whether it favors packet switching, circuit switching, or neither. Scenario: Favors Packet Switching Favors Circuit Switching Neither i. Bursty Data X ii. Narrow bandwidth relative to user demand for transferring data X X iii. Delay Sensitive Applications X (for ii. Both answers are acceptable)
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3. (5) List and briefly describe all of the application and transport layer protocols used to download a webpage. Application Layer – HTTP for downloading web content DNS for obtaining IP address of server Transport Layer – TCP for carrying HTTP requests/responses UDP for carrying DNS requests/responses 4. (15)
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