Description
Questions:
You are required to ONLY answer the following questions from the attached
questions document “HomeAssign_2_Questions.pdf”:
Question
P.4
P.5
P.7
P.8
P.9
P.10
P4. Consider the following string of ASCII characters that were captured by Wireshark when the browser sent an HTTP GET message (i.e., this is the actual content of an HTTP GET message). The characters are carriage return and line-feed characters (that is, the italized character string 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.html HTTP/1.1Host: gai a.cs.umass.eduUser-Agent: Mozilla/5.0 ( Windows;U; Windows NT 5.1; en-US; rv:1.7.2) Gec ko/20040804 Netscape/7.2 (ax) Accept:ex t/xml, application/xml, application/xhtml+xml, text /html;q=0.9, text/plain;q=0.8,image/png,*/*;q=0.5 Accept-Language: en-us,en;q=0.5AcceptEncoding: zip,deflateAccept-Charset: ISO -8859-1,utf-8;q=0.7,*;q=0.7Keep-Alive: 300 Connection:keep-alive 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. 172 CHAPTER 2 • APPLICATION LAYER HTTP/1.1 200 OKDate: Tue, 07 Mar 2008 12:39:45GMTServer: Apache/2.0.52 (Fedora) Last-Modified: Sat, 10 Dec2005 18:27:46 GMTETag: “526c3-f22-a88a4c80”AcceptRanges: bytesContent-Length: 3874 Keep-Alive: timeout=max=100Connection: Keep-AliveContent-Type: text/html; charset= ISO-8859-1<!doctype html public “- //w3c//dtd html 4.0 transitional//en”>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
small amount of HTML text. Let RTT0 denote the RTT between the local host
and the server containing the object. Assuming zero transmission time of the
object, how much time elapses from when the client clicks on the link until
the client receives the object?
P8. Referring to Problem P7, suppose the HTML file references eight very small
objects on the same server. Neglecting transmission times, how much time
elapses with
a. Non-persistent HTTP with no parallel TCP connections?
b. Non-persistent HTTP with the browser configured for 5 parallel connections?
c. Persistent HTTP?
P9. Consider Figure 2.12, for which there is an institutional network connected to
the Internet. Suppose that the average object size is 850,000 bits and that the
average request rate from the institution’s browsers to the origin servers is 16
requests per second. Also suppose that the amount of time it takes from when
the router on the Internet side of the access link forwards an HTTP request
until it receives the response is three seconds on average (see Section 2.2.5).
Model the total average response time as the sum of the average access delay
(that is, the delay from Internet router to institution router) and the average
Internet delay. For the average access delay, use ∆/(1 – ∆!), where ∆ is the
average time required to send an object over the access link and ! is the
arrival rate of objects to the access link.
a. Find the total average response time.
b. Now suppose a cache is installed in the institutional LAN. Suppose the
miss rate is 0.4. Find the total response time.
P10. Consider a short, 10-meter link, over which a sender can transmit at a rate of
150 bits/sec in both directions. Suppose that packets containing data are
100,000 bits long, and packets containing only control (e.g., ACK or handshaking) are 200 bits long. Assume that N parallel connections each get 1/N
of the link bandwidth. Now consider the HTTP protocol, and suppose that
each downloaded object is 100 Kbits long, and that the initial downloaded
object contains 10 referenced objects from the same sender. Would parallel
downloads via parallel instances of non-persistent HTTP make sense in this
case? Now consider persistent HTTP. Do you expect significant gains over
the non-persistent case? Justify and explain your answer.