计算机网络课程作业.docx

计算机网络课程作业.docx

《计算机网络课程作业.docx》由会员分享，可在线阅读，更多相关《计算机网络课程作业.docx（18页珍藏版）》请在冰豆网上搜索。

计算机网络课程作业

Chapter1.

R1,R3,R8,R11,R12,R13,R15,R16,R18,R19,R23,R25,R26（R4,R7,R10,R14,R20,R22,R24）

p2,p5,p7,p8,p9,p12,p13,p22,p24,p26（p3,p6,p10,p11,p14,p15,p17,p18,p19,p20,p21）

R1.

None.

Serversandclients.

Yes.

R3.

Aclientprogramisaprogramrunningononeendsystemthatrequestsandreceivesaservicefromaserverprogramrunningonanotherendsystem.

Yes.

R8.

Dial-upmodems:

upto56kbps;dedicated.

HFC:

upto30Mbps,2Mbpsupstream;shared.

DSL:

upto1Mbpsupstream,upto8Mbpsdownstream;dedicated.

R11.

Moresuitableforreal-timeservices;providingastablebandwidth;noworryaboutdelayandloss;noneedofanalysiswhiledatatransfer

Moresuitablefordigitalsignaltransfer.

R12.

L/R1+L/R2

R13.

Becausepacketswitchingprovideson-demandsharingofresourcesinsteadofpre-allocated.WhileTDMdecidesthebandwidthofeachsender-receiverpairinadvance.

R15.

Tier-1ISPsareeachdirectlyconnectedonlytoeachoftheothertier-1ISPs,whilecanbeeachconnectedtoalargenumberoftier-2ISPs.

R16.

Processingdelay,transmissiondelay,propagationdelay,andqueuingdelay.Thequeuingdelayisvariable（dependsoncongestionlevelofrouter）andtheotherthreeareallconstant.

R18.

Rate:

RPropagationdelay:

DPacketsize:

L

WhenL/RD,thefirstbitofthepacketreachesthereceiverbeforethesenderfinishestransmitting.

R19.

a.250kbps

b.2M*8/250k=64s

c.200kbps;80s

R23.

Applicationlayer,transportlayer,networklayer,linklayer,physicallayer.

Application:

coversthereactionbetweendifferentapplications

Transport:

transferringmessagesbetweenapplicationendpoints

Network:

movingnetwork-layerpacketsfromonehosttoanother

Link:

routingadatagramthroughaseriesofroutersbetweenthesourcesanddestinations

Physical:

movingentireframesfromonenetworkelementtoanadjacentnetworkelement

R25.

Theyarethepacketdataunitsofeachlayer.

R26.

Wormsaremalwarethatcanenteradevicewithoutanyexplicituserinteraction.

Virusesaremalwarethatrequiresomeformofuserinteractiontoinfecttheuser’sdevice.

Trojanhorseismalwarethatisahiddenpartofsomeotherwiseusefulsoftware.

（?

）P2.

a.6

b.4

P5.

a.m/s

b.L/R

c.m/s+L/R

d.justlefthostA

e.adistanceofs*L/RfarfromhostA

f.hasreachedhostB

g.m=s*L/R=250M*100/28k=25,000km

P7.

a.10

b.0.1

c.0.1ⁿ*0.9⁽⁴⁰⁻ⁿ⁾*C₄₀ⁿ

d.λ=40*0.1=4,P（X≥11）=0.002840

P8.

a.1G/100k=1000

b.λ=p*M,P（X≥N+1）

P9.

a.L/R₁+d₁/s₁+L/R₂+d₂/s₂

b.2*1000*8bits/1Mbps+2*0.002second+（6000+3000）km/250000（km/s）=0.056second

P12.

a.3.5*1250*8bits/1Mbps=0.035second

b.（n*L-x）/R

P13.

（0+L/R+2L/R+…+（N-1）L/R）/N=（N-1）L/2R

P22.

a.（h=36000km）dprop=36000km/2*10⁸（km/s）=0.00018s

b.R∙dprop=10Mbps*0.00018s=1800Mb

c.x=R∙dprop=1800Mb

P24.

a.tothefirstpacketswitch:

8∙10⁶bits/2Mbps=4s

todestinationhost:

3*4s=12s

b.2000bits/2Mbps=0.001s

whent=0.001s

whent=0.002s

c.4000*0.001s+0.002s=4.002s

comment:

Messagesegmentationsavetimewhilepacketswitch

d.Ifoneofthedatasegmentsgetslost,mistakewilloccurinthereceivedfile,sothesegmentshavetobeaddedaordermark.

P26.

F/S*L/R+L/R=FL/SR+L/R

Chapter2.

R1,R3,R4,R5,R10,R11,R13,R15,R16,R20,R21,R22,R27,R28

P1,P4,P5,P7,P8,P16,P24,P25

R1.

TheWeb:

HTTP;Filetransfer:

FTP;ElectronicmailintheInternet:

SMTP;Remoteterminalaccess:

Telnet;Streamingmultimedia:

HTTP

R3.

Fromtheapplicationdeveloper’sperspective,thenetworkarchitectureisfixedandprovidesaspecificsetofservicestoapplications.Theapplicationarchitecture,ontheotherhand,isdesignedbytheapplicationdeveloperanddictateshowtheapplicationisstructuredoverthevariousendsystems.

R4.

Theportnumber.

R5.

Notexactly.Althoughthehostscanallperformaseitherclientsandservers,thereisstilladifferencebetweenthesenderandreceiverofthefileduringacommunicationsession.Thesendercouldbeseenastheserversideandthereceivercouldbeseenastheclientside.

R10.

Transportlayer.

Inparticular,ifanapplicationwantstousetheservicesofSSL,itneedstoincludeSSLcode（existing,highlyoptimizedlibrariesandclasses）inboththeclientandserversidesoftheapplication.

R11.

Ahandshakingprotocolisaprotocolwhichsendsacontrolmessagetothereceiverbeforestartingtotransferringtherequesteddata.（likeSMTP）

R13.

R15.

a.Aliceinvokesheruseragentfore-mail,providesBob’se-mailaddress,composesamessage,andinstructstheuseragenttosendthemessage.

b.Alice’suseraentsendsthemessagetohermailserver,whereitisplacedinamessagequeue.

c.TheclientsideofSMTP