Computer fNetworking fA fTop-Down fApproach, f8th fEdition fby fJames fKuros
© f2020 fPearson fEducation, fHoboken, fNJ. fAll frights
freserved. stumerit@gmail.com
,Computer fNetworking: fA fTop-Down fApproach,
th f
f8 Edition
Solutions fto fReview fQuestions fand fProblems
Version fDate: fAugust f2020
This fdocument fcontains fthe fsolutions fto freview fquestions fand fproblems ffor fthe f8th
fedition fof fComputer fNetworking: fA fTop-Down fApproach fby fJim fKurose fand fKeith
fRoss. fThese fsolutions fare fbeing fmade favailable fto finstructors fONLY. f Please fdo
fNOT fcopy for fdistribute fthis fdocument fto fothers f(even fother finstructors). fPlease fdo
fnot fpost fany fsolutions fon fa fpublicly-available fWeb fsite. fWe’ll fbe fhappy fto fprovide
fa fcopy f(up-to-date) fof fthis fsolutionfmanual fourselves fto fanyone fwho fasks.
Acknowledgments: fOver fthe fyears, fseveral fstudents fand fcolleagues fhave fhelped fus
fprepare fthis fsolutions fmanual. fSpecial fthanks fgoes fto fHonggang fZhang, fRakesh
fKumar, fPrithula fDhungel, fVijay fAnnapureddy, fYifan fZhou. fAlso fthanks fto fall fthe
freaders fwho fhave fmade fsuggestions fand fcorrected ferrors.
All fmaterial f© fcopyright f1996-2020 fby fJ.F. fKurose fand fK.W. fRoss. fAll frights freserved
© f2020 fPearson fEducation, fHoboken, fNJ. fAll frights
freserved. stumerit@gmail.com
,Chapter f1 fReview fQuestions
1. There fis fno fdifference. fThroughout fthis ftext, fthe fwords f“host” fand f“end fsystem”
fare fused finterchangeably. fEnd fsystems finclude fPCs, fworkstations, fWeb fservers,
fmail fservers, fPDAs, fInternet-connected fgame fconsoles, fetc.
2. From fWikipedia: fDiplomatic fprotocol fis fcommonly fdescribed fas fa fset fof
finternational fcourtesy frules. fThese fwell-established fand ftime-honored frules fhave
fmade fit feasier ffor fnations fand fpeople fto flive fand fwork ftogether. fPart fof
fprotocol fhas falways fbeen fthe facknowledgment fof fthe fhierarchical fstanding fof fall
fpresent. fProtocol frules fare fbased fonfthe fprinciples fof fcivility.
3. Standards fare fimportant ffor fprotocols fso fthat fpeople fcan fcreate fnetworking fsystems
fandfproducts fthat finteroperate.
4. 1. fDial-up fmodem fover ftelephone fline: fhome; f2. fDSL fover ftelephone fline: fhome
for fsmall foffice; f3. fCable fto fHFC: fhome; f4. f100 fMbps fswitched fEthernet:
fenterprise.
5. HFC fbandwidth fis fshared famong fthe fusers. fOn fthe fdownstream fchannel, fall
fpackets femanate ffrom fa fsingle fsource, fnamely, fthe fhead fend. fThus, fthere fare fno
fcollisions fin fthe fdownstream fchannel.
6. In fmost fAmerican fcities, fthe fcurrent fpossibilities finclude: fdial-up; fDSL; fcable
fmodem;ffiber-to-the-home.
7. Ethernet fLANs fhave ftransmission frates fof f10 fMbps, f100 fMbps, f1 fGbps fand f10 fGbps.
8. Today, fEthernet fmost fcommonly fruns fover ftwisted-pair fcopper fwire. fIt falso fcan frun
foverffibers foptic flinks.
9. ADSL: fup fto f24 fMbps fdownstream fand f2.5 fMbps fupstream, fbandwidth fis
fdedicated; fHFC, frates fup fto f42.8 fMbps fand fupstream frates fof fup fto f30.7 fMbps,
fbandwidth fis fshared. fFTTH: f2-10Mbps fupload; f10-20 fMbps fdownload;
fbandwidth fis fnot fshared.
10. There fare ftwo fpopular fwireless fInternet faccess ftechnologies ftoday:
a. Wifi f(802.11) fIn fa fwireless fLAN, fwireless fusers ftransmit/receive fpackets
fto/from fan fbase fstation f(i.e., fwireless faccess fpoint) fwithin fa fradius fof ffew
ftens fof fmeters. fThe fbase fstation fis ftypically fconnected fto fthe fwired
fInternet fand fthusfserves fto fconnect fwireless fusers fto fthe fwired fnetwork.
b. 3G fand f4G fwide-area fwireless faccess fnetworks. fIn fthese fsystems, fpackets
fare ftransmitted fover fthe fsame fwireless finfrastructure fused ffor fcellular
ftelephony, fwith fthe fbase fstation fthus fbeing fmanaged fby fa
ftelecommunications fprovider. fThis fprovides fwireless faccess fto fusers
fwithin fa fradius fof ftens fof fkilometers fof fthe fbase fstation.
11. At ftime ft0 fthe fsending fhost fbegins fto ftransmit. fAt ftime ft1 f= fL/R1, fthe fsending
fhost fcompletes ftransmission fand fthe fentire fpacket fis freceived fat fthe frouter f(no
fpropagation fdelay). f Because f the f router f has f the f entire fpacket f at f time f t1, fit f can
f begin f to f transmit f the
© f2020 fPearson fEducation, fHoboken, fNJ. fAll frights
freserved. stumerit@gmail.com
, packet fto fthe freceiving fhost fat ftime ft1. fAt ftime ft2 f= ft1 f+ fL/R2, fthe frouter
fcompletes ftransmission fand fthe fentire fpacket fis freceived fat fthe freceiving fhost
f(again, fno fpropagation fdelay). fThus, fthe fend-to-end fdelay fis fL/R1 f + fL/R2.
12. A fcircuit-switched fnetwork fcan fguarantee fa fcertain famount fof fend-to-end
fbandwidth ffor fthe fduration fof fa fcall. fMost fpacket-switched fnetworks ftoday
f(including fthe fInternet) fcannot fmake fany fend-to-end fguarantees ffor fbandwidth.
fFDM frequires fsophisticated fanalog fhardware fto fshift fsignal finto fappropriate
ffrequency fbands.
13. a) f 2 fusers fcan fbe fsupported fbecause feach fuser frequires fhalf fof fthe flink fbandwidth.
b) Since feach fuser frequires f1Mbps fwhen ftransmitting, fif ftwo for ffewer fusers
ftransmit fsimultaneously, fa fmaximum fof f2Mbps fwill fbe frequired. fSince fthe
favailable fbandwidth fof fthe fshared flink fis f2Mbps, fthere fwill fbe fno fqueuing
fdelay fbefore fthe flink. fWhereas, fif fthree fusers ftransmit f simultaneously, f the
fbandwidth f required fwill fbe f3Mbps fwhich fis fmore fthan fthe favailable
fbandwidth fof fthe fshared flink. fIn fthis fcase, fthere fwill fbe fqueuing fdelay
fbefore fthe flink.
c) Probability fthat fa fgiven fuser fis ftransmitting f= f0.2
d) Probability fthat fall fthree fusers fare ftransmitting fsimultaneously f= f
3
= f (0.2) f= f 0.008. f Since f the f queue f grows f when f all f the f users f are
f transmitting, f theffraction f of f time f during f which f the f queue f grows f (which f is
f equal f to f the f probability
that fall fthree fusers fare ftransmitting fsimultaneously) fis f0.008.
14. If fthe ftwo fISPs fdo fnot fpeer fwith feach fother, fthen fwhen fthey fsend ftraffic fto
feach fother fthey fhave fto fsend fthe ftraffic fthrough fa fprovider fISP f(intermediary),
fto fwhich fthey fhave fto fpay ffor fcarrying fthe ftraffic. fBy fpeering fwith feach fother
fdirectly, fthe ftwo fISPs fcan freduce ftheir fpayments fto ftheir fprovider fISPs. fAn
fInternet fExchange fPoints f(IXP) f(typically fin fa fstandalone fbuilding fwith fits fown
fswitches) fis fa fmeeting fpoint fwhere fmultiple fISPs fcan fconnect fand/or fpeer
ftogether. fAn fISP fearns fits fmoney fby fcharging feach fof fthe fthe fISPs fthat fconnect
fto fthe fIXP fa frelatively fsmall ffee, fwhich fmay fdepend fon f the f amount f of f traffic
f sent f to f or f received f from f the f IXP.
15. Google's fprivate fnetwork fconnects ftogether fall fits fdata fcenters, fbig fand fsmall.
fTraffic fbetween fthe fGoogle fdata fcenters fpasses fover fits fprivate fnetwork frather
fthan fover fthe fpublic fInternet. fMany fof fthese fdata fcenters fare flocated fin, for
fclose fto, flower ftier fISPs. fTherefore, fwhen fGoogle fdelivers fcontent fto fa fuser, fit
foften fcan fbypass fhigher ftier fISPs. fWhat fmotivates fcontent fproviders fto fcreate
fthese fnetworks? fFirst, fthe fcontent fprovider fhas fmore fcontrol fover fthe fuser
fexperience, fsince fit fhas fto fuse ffew fintermediary fISPs. fSecond, fit fcan fsave
fmoney fby fsending fless ftraffic finto fprovider fnetworks. fThird, fif fISPs fdecide fto
fcharge fmore fmoney fto fhighly fprofitable fcontent fproviders f (in fcountries fwhere fnet
fneutrality fdoesn't fapply), fthe fcontent fproviders fcan favoid fthese fextra fpayments.
16. The fdelay fcomponents fare fprocessing fdelays, ftransmission fdelays, fpropagation
fdelays, fand fqueuing fdelays. fAll fof fthese fdelays fare ffixed, fexcept ffor fthe fqueuing
© f2020 fPearson fEducation, fHoboken, fNJ. fAll frights
freserved. stumerit@gmail.com
