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Application Layer
Introduction to network

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### Study guide1(1)

1. 1. CHAPTER 1 Computer Networks and the Internet 1 CH01-02_p1-30 6/15/06 4:34 PM Page 1
8. 8. c. When is the delay longer for packet switching than for circuit switching assuming Interpret your result. 18. Protocol layers. a. What are the five protocol layers, from top to bottom, in the Internet? b. For each of the five layers, what is the name of the packets processed at the layer? c. An end-system processes up to which layer? d. A router processes up to which layer? e. A link-layer switch processes up to which layer? h = 0.5? 8 STUDY COMPANION FOR COMPUTER NETWORKING, THIRD EDITION CH01-02_p1-30 6/15/06 4:34 PM Page 8
11. 11. Note that here we used the well-known fact that 15. Thus, we have: The transmission delay for each case is The total delay is the queuing delay plus the transmission delay. For the four cases, this is 14.3 msec, 25 msec, 100 msec, and 1 sec. 16. The roundtrip to router 8 is 13.1 msec and the roundtrip delay to router 9 is 12.7. Two separate roundtrip probes were sent to routers 8 and 9 at two (slight- ly) different times. During these times, congestion in the links along the path changed. Apparently there was more congestion in at least one of the first eight links during the first probe than in the second probe; hence, the roundtrip delay to router 8 is greater than the roundtrip delay to router 9. The two largest de- lays occur between routers 3 and 4 and between routers 4 and 5. Routers 3 and 4 appear to be located in Amherst Massachusetts (UMass) and Boston. Routers 4 and 5 appear to be located in Boston and New York City. 17. a. The time required to transmit the packet over one link is The time required to transmit the packet over Q links is Thus, the total delay for packet switching is b. For circuit switching, bits are not “store and forwarded” before each link. Thus, there is only one transmission delay of The total delay is c. The delay is longer for packet switching when or equivalently when Thus, if there are more than 16 links, packet switching has a larger delay, due to the store and forwarding. If there are fewer than 16 links, circuit switching has a larger delay, due to its reduced transmission rate 18. a. application, transport, network, link, physical b. message, segment, datagram, frame, packet c. an end-system processes up through the application layer d. a router processes up through the network layer e. a link-layer switch processes up through the link layer (R>24). Q 7 16.Q(1 + h)F>R + ts 7 24F>R + ts 24F>R + ts. F>(R>24) = 24F>R. Q(1 + h)F>R + ts. Q(1 + h)F>R. (1 + h)F>R. L>R = 10 msec. a = 99; I = .99, average queuing delay = (.99>.01) 10 msec = 990 msec a = 90; I = .9, average queuing delay = (.9>.1) 10 msec = 90 msec a = 60; I = .6, average queuing delay = (.6>.4) 10 msec = 15 msec a = 30: I = .3, average queuing delay = (.3>.7) 10msec = 4.3 msec L>R = 10 msec. 1 + 2 + Á + N = N(N + 1)>2. + (N - 1)) = LN(N - 1)>2RN = (N - 1)L>2R (L>R + 2L>R + Á + (N - 1)L>R)>N = L>RN(1 + 2 + Á CHAPTER 1 • COMPUTER NETWORKS AND THE INTERNET 11 CH01-02_p1-30 6/15/06 4:34 PM Page 11
12. 12. CH01-02_p1-30 6/15/06 4:34 PM Page 12
13. 13. CHAPTER 2 The Application Layer 13 CH01-02_p1-30 6/15/06 4:34 PM Page 13
17. 17. actual content of an HTTP GET message). The characters <cr><lf> are car- riage return and line feed characters (that is, the italicized 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 answers. CHAPTER 2 • THE APPLICATION LAYER 17 GET /cs453/index.html HTTP/1.1<cr><lf>Host: gai a.cs.umass.edu<cr><lf>User-Agent: Mozilla/5.0 ( Windows;U; Windows NT 5.1; en-US; rv:1.7.2) Gec ko/20040804 Netscape/7.2 (ax) <cr><lf>Accept:ex t/xml,application/xml,application/xhtml+xml,text /html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5 <cr><lf>Accept-Language: en-us,en;q=0.5..Accept- Encoding: zip,deflate<cr><lf>Accept-Charset: ISO -8859-1,utf-8;q=0.7,*;q=0.7..Keep-Alive: 300<cr> <lf>Connection:keep-alive<cr><lf><cr><lf> a. What is the URL of the document requested by the browser? Make sure you give the hostname and the file name parts of the URL. b. What version of HTTP is the browser running? c. Is a Netscape or an Internet Explorer browser making the request? d. Is the browser requesting a non-persistent or a persistent connection? e. What is the IP address of the computer on which the browser is running? 7. More HTTP basics. The text below shows the reply sent from the server in response to HTTPP GET message in Question 6. Answer the following ques- tions, indicating where in the message below you find the answers. HTTP/1.1 200 OK<cr><lf>Date: Tue, 07 Mar 2006 12:39:45GMT..Server: Apache/2.0.52 (Fedora) <cr><lf>Last-Modified: Sat, 10 Dec 2005 18:27:46 GMT<cr><lf>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 4.0 transitional//en"><lf><html><lf><head><lf> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><lf> <meta name="GENERATOR" content="Mozilla/4.79 [en] (Windows NT 5.0; U) Netscape]"><lf> <title>CMPSCI 453 / 591 / NTU-ST550A Spring 2005 homepage</title><lf></head><lf> <much more document text following here (not shown)> CH01-02_p1-30 6/15/06 4:34 PM Page 17