计算机网络英文版复习知识教材课程PPT格式课件下载.ppt

1、Computer NetworkingFinal Review,Jinghui Qin,Content,Computer Networks and the InternetApplication Layer Transport LayerThe Network LayerThe Link and Local Area NetworksWireless and Mobile Networks,Computer Networks and the Internet,Some basic conceptsprotocolcircuit switchingpacket switchingetc.Dela

2、y,Loss and Throughput in Packet-Switched Networksprocessing delayqueuing delaytransmission delay,Computer Networks and the Internet,propagation delayend-to-end delay computationthroughput:#instantaneous,averageProtocol Layers and Their Service ModelsSeven-layer ISO OSI reference modelFive-layer Inte

3、rnet protocol stackThe function of each layer,Computer Networks and the Internet,Problem 1-P5,Computer Networks and the Internet,Problem 1-P5,Computer Networks and the Internet,Solution 1-P5,Computer Networks and the Internet,Problem 2-P17,Computer Networks and the Internet,Solution 2-P17Throughput=

4、minRs,Rc,R/M,Application Layer,Some basic conceptsclientserversocketTransport Services Provided by InternetTCP services:#connection-oriented&#reliable data transferUDP services Application-Layer Protocol,Application Layer,HTTPNon-persistent and Persistent HTTP Message FormatRequest MessageResponse M

5、essageCookies,Application Layer,FTPtwo parallel connections out-of-band&#in-bande-mailSMTPPOP3IMAP,Application Layer,DNSService provided by DNSDNS Working MechanismDNS Records and Message,Application Layer,Problem-P2,Application Layer,Problem-P2,Application Layer,Problem-P2,Application Layer,Solutio

6、n-P2a）The document request was http:#/gaia.cs.umass.edu/cs453/index.html.The Host:#field indicates the servers name and/cs453/index.html indicates the file name.b）The browser is running HTTP version 1.1,as indicated just before hte first pair.c）The browser is requesting a persistent connection,as in

7、dicated by the Connection:#keep-alive.,Application Layer,Solution-P2d）This is a trick question.This information is not contained in an HTTP message anywhere.So there is no way to tell this from looking at the exchange of HTTP messages alone.One would need information from the IP datagrams（that carri

8、ed the TCP segment that carried the HTTP GET request）to answer this question.,Transport Layer,UDPUDP Segment StructureUDP ChecksumThe advantages of UDPPrinciples of Reliable Data TransferSRGBN,Transport Layer,TCPTCP Segment StructureTCP flow controlTCP congest controlAIMDSlow startReaction To Timeou

9、t Events,Transport Layer,Problem 1-P23Consider transferring an enormous file of L bytes from Host A to Host B.Assume an MSS of 1,460 bytes.a.What is the maximum value of L such that TCP sequence numbers are not exhausted?#Recall that the TCP sequence number field has 4 bytes.,Transport Layer,Problem

10、 1-P23b.For the L you obtain in（a）,find how long it takes to transmit the file.Assume that a total of 66 bytes of transport,network,and data-link header are added to each segment before the resulting packet is sent out over a 100 Mbps link.Ignore flow control and congestion control so A can pump out

11、 the segments back to back and continuously.,Transport Layer,Solution 1-P23,Transport Layer,Solution 1-P23,Transport Layer,Problem 2-P34,Transport Layer,Problem 2-P34,Transport Layer,Problem 2-P34,Transport Layer,Solution 2-P34a）TCP slowstart is operating in the intervals 1,6 and 23,26b）TCP congesti

12、on advoidance is operating in the intervals 6,16 and 17,22c）After the 16th transmission round,packet loss is recognized by a triple duplicate ACK.If there was a timeout,the congestion window size would have dropped to 1.,Transport Layer,Solution 2-P34d）After the 22nd transmission round,segment loss

13、is detected due to timeout,and hence the congestion window size is set to 1.e）The threshold is initially 32,since it is at this window size that slowtart stops and congestion avoidance begins.f）The threshold is set to half the value of the congestion window when packet loss is detected.When loss is

14、detected during transmission round 16,the congestion windows size is 42.Hence the threshold is 21 during the 18th transmission round.,Transport Layer,Solution 2-P34g）The threshold is set to half the value of the congestion window when packet loss is detected.When loss is detected during transmission

15、 round 22,the congestion windows size is 26.Hence the threshold is 13 during the 24th transmission round.i）The congestion window and threshold will be set to half the current value of the congestion window（8）when the loss occurred.Thus the new values of the threshold and window will be 4.,Transport

16、Layer,Solution 2-P34H）During the 1st transmission round,packet 1 is sent;#packet 2-3 are sent in the 2nd transmission round;#packets 4-7 are sent in the 3rd transmission round;#packets 8-15 are sent in the 4th transmission round;#packets15-31 are sent in the 5th transmission round;#packets 32-63 are sent in the 6th transmission round;#packets 64 96 are sent in the 7th transmission round.Thus packet 70 is sent in the 7th transmission round.,The Network Layer,Virtual-Circuit NetworksDatagram Networkslongest pre