宁波大学计算机网络协议题.doc

1.
ThequantityLa/Risusefulingaininganintuitiveunderstandingoftheextentofthequeuingdelay.Inparticular,iftrafficintensityisclosetozero,thenpacketarrivalsarefewandfarbetweenanditisunlikelythatanarrivingpacketwillfindanotherpacketinthequeue.Hence,theaveragequeuingdelaywillbeclosetozero.Ontheotherhand,whenthetrafficintensityiscloseto1,therewillbeintervalsoftimewhenthearrivalrateexceedsthetransmissioncapacity(duetotheburstinessofarrivals),andaqueuewillform.Asthetrafficintensityapproaches1,theaveragequeuelengthgetslargerandlarger.ThequalitativedependenceofaveragequeuingdelayonthetrafficintensityisshowninFigure1.20.
Figure1.20:Dependenceofaveragequeuingdelayontrafficdensity
OneimportantaspectofFigure1.20isthefactthatasthetrafficintensityapproaches1,theaveragequeuingdelayincreasesrapidly.Asmallpercentageincreaseintheintensitywillresultinamuchlargerpercentage-wiseincreaseindelay.
根据文献中的论述，用中文分析和回答以下问题：
什么条件下节点的排队延时非常小？（2分）
什么条件下节点的排队延时不断加大？（2分）
什么条件下节点的排队延时变得非常大？（2分）
用你生活中的例子解释“Asmallpercentageincreaseintheintensitywillresultinamuchlargerpercentage-wiseincreaseindelay.”（4分）

2.
ThegeneralformatforaHTTPrequestmessage,asshowninFigure2.7.
Figure2.7:Generalformatofarequestmessage
Weseethatthegeneralformatofarequestmessagecloselyfollowsourearlierexample.Youmayhavenoticed,however,thataftertheheaderlines(andtheadditionalcarriagereturnandlinefeed)thereisan"entitybody."TheentitybodyisnotusedwiththeGETmethod,butisusedwiththePOSTmethod.TheHTTPclientusesthePOSTmethodwhentheuserfillsoutaform--forexample,whenausergivessearchwordstoasearchenginesuchasGoogle.WithaPOSTmessage,theuserisstillrequestingaWebpagefromtheserver,butthespecificcontentsoftheWebpagedependonwhattheuserenteredintotheformfields.IfthevalueofthemethodfieldisPOST,thentheentitybodycontainswhattheuserenteredintotheformfields.TheHEADmethodissimilartotheGETmethod.WhenaserverreceivesarequestwiththeHEADmethod,itrespondswithanHTTPmessagebutitleavesouttherequestedobject.TheHEADmethodisoftenusedbyHTTPserverdevelopersfordebugging.
根据文