lab2_solution

lab2_solution - EC 441: Introduction to Computer Networking...

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EC 441: Introduction to Computer Networking Fall 2008 Lab 2 Solutions 2.0 Prelab Question 1 True or False: For credit, please provide a brief justification to every answer. a) Suppose a user requests a Web page that consists of some text and two images. For this page, the client will send one request and receives three responses. Answer: False. For both HTTP/1.0 & 1.1, N objects need N requests. Here, the web page consists of three objects: text and two images. Therefore, 3 requests are needed. b) Two distinct Web pages (for instance people.bu.edu/staro/index.html and people.bu.edu/staro/publications.html) can be sent over the same persistent connection. Answer: True. It’s possible with HTTP 1.1. Since these two pages are on the same server, they can be transmitted within one TCP connection. c) With non-persistent connections between a browser and an origin server, it is possible for a single TCP segment to carry two distinct HTTP request messages. Answer: False. Only 1 request can be carried in a non-persistent connection, as is the character of HTTP/1.0. d) The Date: header in the HTTP response message indicates when the object in the response was last modified. Answer: False. The “Date” refers to the time of response. The last modified time of the object is given in the “Last-Modified” entry instead.
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Question 2 Suppose a client downloads a Web page consisting of 1 base html file and N figures (e.g, gif or jpeg files). a) What is the end-to-end delay for downloading this Web page, if HTTP/1.0 is used? Express your answer as a function of the network round-trip-time between the client and the server. In this and the following two questions, ignore delays associated with DNS queries. Answer: In HTTP/1.0, every object needs a connection. For each of them, 1 RTT is mandatory for TCP connection and 1 RTT for request and response. Here we have N+1 objects. Thus, the total end-to-end delay is 2*( N+1 )* RTT , plus the transfer time of these files. b) What is the end-to-end delay for downloading this Web page, if HTTP/1.1 is used? Answer:
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lab2_solution - EC 441: Introduction to Computer Networking...

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