第一章
1. Consider nding a packet of F bits over a path of Q links. Each link transmits at R bps. The network is lightly loaded so that there are no queuing delays. Propagation delay is negligible.
a. Suppo the network is a packet-switched virtual-circuit network. Denote the VC tup time by ts conds. Suppo the nding layers add a total of h bits of header to the packet. How long does it take to nd the file from source to destination?
b. Suppo the network is a packet-switched datagram network and a connectionless rvice is ud. Now suppo each packet has 2h bits of header. How long does it take to nd the packet?
c. Finally, suppo that the network is a circuit-switched network. Further suppo that the transmission rate of the circuit between source and destination is R bps. Assuming ts tup time and h bits of header appended to the packet, how long does it take to nd the packet?
1、
a. ts+(F+h)/R*Q
b. (F+2h)/R*Q
c. C.ts+(F+h)/R
2. This elementary problem begins to explore propagation delay and transmission delay, two central concepts in data networking. Consider two hosts, A and B, connected by a single link of rate R bps. Suppo that the two hosts are parated by m meter, and suppo the propagation speed along the link is s meters/c. Host A is to nd a packet of size L bits to Host B.
a. Express the propagation delay, dprop, in terms of m and s.
b. Determine the transmission time of the packet, dtrans, in terms of L and R.
c. Ignoring processing and queuing delays, obtain an expression for the end-to-end dealy.
d. Suppo Host A begins to transmit the packet at time t=0. At time t=dtrans, where is the last bit of the packet?
e. Suppo dprop is greater than dtrans. At time t= dtrans, where is the first bit of the packet?
f. Suppo dprop is less than dtrans. At time t=dtrans, where is the first bit of the packet?
g. Suppo s=2.5·108, L=100bits, and R=28kbps. Find the distance m so that dprop equals dtrans.
2、
a) m/s
b) L/R
c) m/s+ L/R
d) Interface of host A
e) s*dtrans=s*L/R
f) Host B
g) m/s= L/R=> m=8.928*105
第二章
1. In the following figure, Alice nds an e-mail to Bob, and Bob gives a reply to Alice. If Alice and Bob both u mail ur agent, plea write what protocol is ud in procedure①～⑥? If both Alice and Bob u Web browr, what protocol is ud in procedure①～⑥?
（1）①SMTP; ②POP3 or IMAP; ③SMTP; ④SMTP; ⑤POP3 or IMAP; ⑥SMTP
（2）①HTTP; ②HTTP; ③SMTP; ④SMTP; ⑤HTTP; ⑥HTTP
2. A client requests a Web page jw./jwzx/index.do from a rver through IE browr. The version of HTTP is 1.1 and default connection is persistent connection. The page is supported in Chine. Plea write the request message.
If the rver gives a reply to the client, the respon message is created at 8:00:00 on 27-09-2011, and the object is modified at 00:00:00 on 18-09-2011. Plea write the respon message.
The known-conditions are: rver is apache/2.0.40; the object is a text file and consists 1796 bytes.
If there is a proxy rver between the client and the Web rver, how does the proxy rver check the page it caches is newer or older?
（1） GET /jwzx/index.do HTTP/1.1
Host: jw.
Connection: Keep-Alive
Ur-agent: Mozilla/4.0
Accept-language: zh-cn
（2） HTTP/1.1 200 OK
Date: Tue, 27 Sep 2011 08:00:00 GMT
Server: Apache/2.0.40
Content-Length: 1796
Content-Type: text/html
Last-Modified: Sun, 18 Sep 2011 00:00:00 GMT
（3） the proxy rver us conditional GET
GET /jwzx/index.do HTTP/1.1
Host: jw.
If-modified-since: Sun, 18 Sep 2011 00:00:00 GMT
第三章
1. Consider a TCP connection between Host A and Host B. Suppo that the TCP gments traveling from Host A to Host B have source port number x and destination port number y. What are the source and destination port numbers for the gments traveling from Host B to Host A?
Source port number is y, destination port number is x.
2. True of Fal?
(1) Host A is nding Host B a large file over a TCP connection. Assume Host B has no data to nd Host A. Host B will not nd acknowledgments to Host A becau Host B can not piggyback the acknowledgments on data.×
(2) The size of the TCP RcvWindow never changes throughout the duration of the connection. ×
(3) Suppo Host A is nding Host B a large file over a TCP connection. The number of unacknowledged bytes that A nds cannot exceed the size of the receive buffer. ×
