第二章
1. (Q2) 干净用英语怎么说For a communication ssion between a pair of process, which process is the client and which is the rver?
Answer: The process which initiates the communication is the client; the process that waits to be contacted is the rver.陕西医保
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2. (Q3) What is the difference between network architecture and application architecture?
情感空间Answer: Network architecture refers to the organization of the communication process into layers (e.g., the five-layer Internet architecture). Application architecture, on the other hand, is designed by an application developer and dictates the broad structure of the application (e.g., client-rver or P2P)
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3. (Q4) What information is ud by a process running on one host to identify a process running on another host?
Answer: The IP address of the destination host and the port number of the destination socket.
4. (Q6) Referring to Figure 2.4, we e that none of the application listed in Figure 2.4 requires both no data loss and timing. Can you conceive of an application that requires no data loss and that is also highly time-nsitive?
Answer: There are no good example of an application that requires no data loss and timing. If you know of one, nd an e-mail to the authors
5. (Q9) Why do HTTP, FTP, SMTP, and POP3 run on top of TCP rather than on UDP?
Answer: The applications associated with tho protocols require that all application data be received in the correct order and without gaps. TCP provides this rvice whereas UDP does not.
6. (Q11) What is meant by a handshaking protocol?
Answer: A protocol us handshaking if the two communicating entities first exchange control packets before nding data to each other. SMTP us handshaking at the application layer whereas HTTP does not.
7. (Q13) Telnet into a Web rver and nd a multiline request message. Include in the request message the If-modified-since: header line to force a respon message with the 304 Not Modified status code.
Answer: Issued the following command (in Windows command prompt) followed by the HTTP GET message to the “utopia.poly.edu” web rver:
> telnet utopia.poly.edu 80
Since the index.html page in this web rver was not modified since Fri, 18 May 2007 09:23:34 GMT, the following output was displayed when the above commands were issued on Sat, 19 May 2007. Note that the first 4 lines are the GET message and header
lines input by the ur and the next 4 lines (starting from HTTP/1.1 304 Not Modified) is the respon from the web rver.
8. (Q14) Consider an e-commerce site that wants to keep a purcha record for each of its customers. Describe how this can be done with cookies.
Answer: When the ur first visits the site, the site returns a cookie number. This cookie number is stored on the ur’s host and is managed by the browr. During each subquent visit (and purcha), the browr nds the cookie number back to the site. Thus the site knows when this ur (more precily, this browr) is visiting the site.
9. (Q15) Suppo Alice, with a Web-bad e-mail account (such as Hotmail or gmail), nds a message to Bob, who access his mail from his mail rver using POP3. Discuss how the message gets from Alice’s host to Bob’s host. Be sure to list the ries of application-layer protocols that are ud to move the message between the two hosts.
Answer:学生评价 Message is nt from Alice’s host to her mail rver over HTTP. Alice’s mail rver then nds the message to Bob’s mail rver over SMTP. Bob then transfers the message from his mail rver to his host over POP3.
10. (Q10) Recall that TCP can be enhanced with SSL to provide process-to-process curity rvices, including encryption. Does SSL operate at the transport layer or the application layer? If the application developer wants TCP to be enhanced with SSL, what does the developer have to do?
strandAnswer: SSL operates at the application layer. The SSL socket takes unencrypted data from the application layer, encrypts it and then pass it to the TCP socket. If the applicati
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on developer wants TCP to be enhanced with SSL, she has to include the SSL code in the application.
11. (Q16) Print out the header of an e-mail message you have recently received. How many Received: header lines are there? Analyze each of the header lines in the message.
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Answer: from 65.54.246.203 (EHLO bay0-omc3-s3.)
