CS118 Midterm 10F Solutions

CS118 Midterm 10F Solutions - CS 118 Computer Networking...

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CS 118 Computer Networking Fundamentals Midterm Exam Fall 2010 Professor Mario Gerla 10/30/2010 Question Points Score 1 15 2 20 3 20 4 20 5 25 Total: 100 Name: _________________________ Student ID #: _____________________ Instructions: - Closed book, one A4 sized Sheet of notes allowed. - Calculators are allowed - This exam has 12 pages, including this cover page
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Problem 1: True/False (1 point each, total 15 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 (Application and Transport interface) b) To send emails, email clients such as Outlook Express connect directly to the recipient’s mail server and use SMTP to “push” the email into their mailbox. TRUE FALSE (Mail delivered to user mail agent which looksup target host’s mail agent) c) Go-Back-N gives better performance than SR on noisy channels. TRUE FALSE (Window will not slide fast) d) If buffer sizes weren’t a limitation, it would be faster in a packet-switched network to send large files as one packet because fewer overall header bits would be required to transmit the file. TRUE FALSE (Packet switched n/w used to allow multiple users to send together) e) Root Name Servers typically handle DNS queries iteratively, rather than recursively. TRUE FALSE f) TCP uses cumulative ACKs, and the ACK number is the number of the last correctly received byte. TRUE FALSE ( The value of ACK field is the next sequence number that the receiver is expecting ) g) The transport layer provides logical communication between two processes, while the network layer provides logical connections between two hosts. TRUE FALSE h) 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. TRUE FALSE (There is error checking in UDP) i) Assuming there is no packet loss, a reliable data transmission does not need error control. TRUE FALSE (Error may be introduced due to noise) j) Client host must know server host’s HTTP port number before making the connection. TRUE FALSE (HTTP runs on Port 80 : Well known port)
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k) HTTP and DNS are both application layer protocols that utilize TCP as their transport layer protocol to ensure that web pages are downloaded without errors, and from the correct server. TRUE FALSE (DNS uses UDP) l) 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 m) TCP’s congestion control mechanism responds differently to a timeout event and a 3- duplicate-ACK event. TRUE FALSE n) 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
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This note was uploaded on 01/15/2012 for the course CS 118 taught by Professor Chu during the Spring '08 term at UCLA.

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CS118 Midterm 10F Solutions - CS 118 Computer Networking...

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