Homework #2 Problem 1,2,3,4,5 Solution



Consider the following string of ASCII characters that were captured by W ireshark when the browser sent an HTTP GET message (i.e., this is the actual content of an HTTP GET message). The characters <CR><LF> are carriage-return and line-feed characters. Answer the following questions, indicating where in the HTTP GET message below you nd the answer.

GET /classes/spring17/cs118/project-1.html HTTP/1.1<CR><LF>

Host: web.cs.ucla.edu<CR><LF>

Connection: keep-alive<CR><LF>

Upgrade-Insecure-Requests: 1<CR><LF>

User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10 12 3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36<CR><LF>


text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8<CR><LF> Referer: http://web.cs.ucla.edu/classes/spring17/cs118/homeworks.html<CR><LF> Accept-Encoding: gzip, deflate, sdch<CR><LF> Accept-Language: en-US,en;q=0.8,lv;q=0.6,ru;q=0.4<CR><LF>

If-None-Match: “5a17-54c4847c4f640-gzip”<CR><LF>

If-Modified-Since: Mon, 03 Apr 2017 19:36:49 GMT<CR><LF>

  1. What is the full URL of the document requested by the browser?

  1. What version of HTTP is the browser running?

  1. What type of browser initiates this message? Why is the browser type needed in an HTTP request message?

  1. Can you nd the IP Address of the host on which the browser is running from the captured HTTP request?

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CS 118 Winter 2019 : Homework 2

Problem 2

For each of the questions below, describe answer in terms of low-level packet sequences, drops, or network-level packet reordering.

  1. A speci c case where HTTP/1.1 wins in performance compared to HTTP/1.0

  1. A speci c case where HTTP with web caching wins in performance compared to HTTP without caching

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CS 118 Winter 2019 : Homework 2

Problem 3

Suppose within your Web browser you click on a link to obtain a Web page. The IP address for the associated URL is cached in your local host, so a DNS look-up is not needed. Suppose that the Web page associated with the link is a small HTML le, consisting only of references to 100 very small objects on the same server. Let RT T0 denote the RTT between the local host and the server containing the object. How much time elapses (in terms of RT T0) from when you click on the link until your host receives all of the objects, if you are using:

  1. HTTP/1.0 without parallel TCP connections?

  1. HTTP/1.0 with parallel TCP connections?

  1. HTTP/1.1 without parallel connections, but with pipelining?

Ignore any processing, transmission, or queuing delays in your calculation.

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CS 118 Winter 2019 : Homework 2

Problem 4

BitTorrent is a communication protocol for peer-to-peer le sharing which is used to distribute data (or les) over the Internet.

  1. Consider a new peer A that joins BitTorrent swarm without possessing any chunks. Since peer A has nothing to upload, peer A cannot become a top uploader for any of the other peers. How then will peer A get the rst chunk?

  1. Explain why BitTorrent is primarily useful for popular les but not for unpopular les.

  1. Consider two DHTs (Distributed Hash Table) with a mesh overlay topology and a circular overlay topology, respectively. What are the advantages and disadvantages of each design?

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CS 118 Winter 2019 : Homework 2

Problem 5

The server tries to distribute a le of F = 15Gbits to N clients (peers). The server has an upload rate of us = 30Mbps, and each peer has a download rate of dp = 2Mbps and upload rate of up = 1Mbps. How long does it take to distribute if there are 1,000 peers for both client-server distribution and P2P distribu-tion.

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