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Week 3 Tut Work
Networking Fundamentals (41092)
University of Technology Sydney
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41092 Network Fundamentals
Week 3. Tutorial Problems
P1. True or false? a. A user requests a Web page that consists of some text and three images. For this page, the client will send one request message and receive four response messages. b. Two distinct Web pages (for example, mit/research.html and mit/students.html) can be sent over the same persistent connection. c. With nonpersistent connections between browser and origin server, it is pos-sible for a single TCP segment to carry two distinct HTTP request messages. d. The Date: header in the HTTP response message indicates when the object in the response was last modified. e. HTTP response messages never have an empty message body.
P3. Assume you open a browser and enter yourbusiness/about.html in the address bar. What happens until the webpage is displayed? Provide details about the protocol(s) used and a high-level description of the messages exchanged.
P4. Consider the following string of ASCII characters that were captured by Wireshark when the browser sent an HTTP GET message (i., this is the actual content of an HTTP GET message). The characters <cr><lf> are carriage return and line-feed characters (that is, the italized character string <cr> in the text below represents the single carriage-return character that was contained at that point in the HTTP header). Answer the following questions, indicating where in the HTTP GET message below you find the answer. GET /cs453/index HTTP/1<cr><lf> Host: gai a.cs.umass<cr><lf> User-Agent: Mozilla/5 ( Windows;U; Windows NT 5; en-US; rv:1.7) Gec ko/20040804 Netscape/7 (ax) <cr><lf> Accept:ex t/xml, application/xml, application/xhtml+xml, text /html;q=0, text/plain;q=0,image/png,/;q=0 <cr><lf> Accept-Language: en-us,en;q=0<cr><lf> Accept-Encoding: zip,deflate<cr><lf> Accept-Charset: ISO -8859-1,utf-8;q=0,*;q=0<cr><lf> Connection:keep-alive<cr><lf> Keep-Alive: 300<cr><lf> <cr><lf>
a. What is the URL of the document requested by the browser? b. What version of HTTP is the browser running? c. Does the browser request a non-persistent or a persistent connection? d. What is the IP address of the host on which the browser is running? e. What type of browser initiates this message? Why is the browser type needed in an HTTP request message?
P5. The text below shows the reply sent from the server in response to the HTTP GET message in the question above. Answer the following questions, indicating where in the message below you find the answer. HTTP/1 200 OK<cr><lf> Date: Tue, 07 Mar 2008 12:39:45GMT<cr><lf> Server: Apache/2.0 (Fedora) <cr><lf> Last-Modified: Sat, 10 Dec2005 18:27:46 GMT<cr><lf>
Kurose & Keith, Computer Networking: A Top-Down Approach, 8th Edition. Pearson
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41092 Network Fundamentals
ETag: ”526c3-f22-a88a4c80”<cr><lf> Accept-Ranges: bytes<cr><lf> Content-Length: 3874<cr><lf> Keep-Alive: timeout=max=100<cr><lf> Connection: Keep-Alive<cr><lf> Content-Type: text/html; charset= ISO-8859-1<cr><lf> <cr><lf> <!doctype html public ”-//w3c//dtd html 4//en”><lf><html><lf> <head><lf> <meta http- equiv=”Content-Type” content=”text/html; charset=iso-8859-1”><lf> <meta name=”GENERATOR” content=”Mozilla/4 [en] (Windows NT 5; U) Netscape]”><lf> <title>CMPSCI 453 / 591 / NTU-ST550ASpring 2005 homepage</title><lf></head><lf> <much more document text following here (not shown)> a. Was the server able to successfully find the document or not? What time was the document reply provided? b. When was the document last modified? c. How many bytes are there in the document being returned? d. What are the first 5 bytes of the document being returned? Did the server agree to a persistent connection?
P7. Suppose within your Web browser, you click on a link to obtain a Web page. The IP address for the associated URL is not cached in your local host, so a DNS lookup is necessary to obtain the IP address. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur an RTT of RTT1,... , RTTn. Further suppose that the Web page associated with the link contains exactly one object, consisting of a large amount of HTML text. Let RTT0 denote the RTT between the local host and the server containing the object. Assuming transmission duration of 0 * RTT0 of the object, how much time elapses from when the client clicks on the link until the client receives the object?
P8. Consider Problem P7 again and assume RTT0 = RTT1 = RTT2 =... RTTn = RTT, Furthermore, assume a new HTML file, small enough to have negligible transmission time, which references nine equally small objects on the same server. How much time elapses with a. non-persistent HTTP with no parallel TCP connections? b. non-persistent HTTP with the browser configured for 6 parallel connections? c. persistent HTTP?
Kurose & Keith, Computer Networking: A Top-Down Approach, 8th Edition. Pearson
2
Week 3 Tut Work
Course: Networking Fundamentals (41092)
University: University of Technology Sydney
