lOMoAR cPSD| 10861280
Solution to Computer Networking A Top-
g g g g g
Down Approach (7thEdition)
g g g
Computer Networks (University of Massachusetts Amherst)
g g g g g
StuDocugisgnotgsponsoredgorgendorsedgbyganygcollegegorguniversity
DownloadedgbygZiadgMysarag(
, lOMoAR cPSD| 10861280
Computer Networking: A Top-
g g g
Down Approach,7th Edition
g g g
Solutions to Review Questions and Problems
g g g g g
Version Date: December 2016
g g g
Thisgdocumentgcontainsgthegsolutionsgtogreviewgquestionsgandgproblemsgforgtheg 7thgeditiong
ofgComputergNetworking:gAgTop-
DowngApproachgbygJimgKurosegandgKeithgRoss.gThesegsolutionsgaregbeinggmadegavailablegt
oginstructorsgONLY.gPleasegdogNOTgcopygorgdistributegthisgdocumentgtogothersg(evengotherg
instructors).gPleasegdognotgpostganygsolutionsgongagpublicly-
availablegWebgsite.gWe’llgbeghappygtogprovidegagcopyg(up-to-
date)gofgthisgsolutiongmanualgourselvesgtoganyonegwhogasks.
Acknowledgments:gOvergthegyears,gseveralgstudentsgandgcolleaguesghaveghelpedg usgprepare
gthisgsolutionsgmanual.gSpecialgthanksggoesgtogHongganggZhang,gRakeshgKumar,gPrithulagD
hungel,gandgVijaygAnnapureddy.gAlsogthanksgtogallgthegreadersgwhoghavegmadegsuggestions
gandgcorrectedgerrors.
Allgmaterialg©gcopyrightg1996-2016gbygJ.F.gKurosegandgK.W.gRoss.gAllgrightsgreserved
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Chapter 1 Review Questions
g g g
1. Theregisgnogdifference.gThroughoutgthisgtext,gthegwordsg“host”gandg“endgsystem”gareguse
dginterchangeably.gEndgsystemsgincludegPCs,gworkstations,gWebgservers,gmailgservers,g
PDAs,g Internet-connectedggamegconsoles,getc.
2. FromgWikipedia:gDiplomaticgprotocolgisgcommonlygdescribedgasgagsetgofginternationalgc
ourtesygrules.gThesegwell-establishedgandgtime-
honoredgrulesghavegmadegitgeasiergforgnationsgandgpeoplegtoglivegandgworkgtogether.gPart
gofgprotocolghasgalwaysgbeengthegacknowledgmentgofgtheghierarchicalgstandinggofgallgpre
sent.gProtocolgrulesgaregbasedgongthegprinciplesgofgcivility.
3. Standardsgaregimportantgforgprotocolsgsogthatgpeoplegcangcreategnetworkinggsystemsgand
gproductsgthatginteroperate.
4. 1.gDial-
upgmodemgovergtelephonegline:ghome;g2.gDSLgovergtelephonegline:ghomegorgsmallgoffic
e;g3.gCablegtogHFC:ghome;g4.g100gMbpsgswitchedgEthernet:genterprise;g5.gWifig(802.11):
g homegandgenterprise:g6.g3Ggandg4G:gwide-areagwireless.
5. HFCgbandwidthgisgsharedgamonggthegusers.gOngthegdownstreamgchannel,gallgpacketsgem
anategfromgagsinglegsource,gnamely,gthegheadgend.gThus,gtheregaregnogcollisionsgingthegdo
wnstreamgchannel.
6. IngmostgAmericangcities,gthegcurrentgpossibilitiesginclude:gdial-
up;gDSL;g cablegmodem;gfiber-to-the-home.
7. EthernetgLANsghavegtransmissiongratesgofg10gMbps,g100gMbps,g1gGbpsgandg10gGbps.
8. Today,gEthernetgmostgcommonlygrunsgovergtwisted-
pairgcoppergwire.gItgalsogcangrungovergfibersgopticglinks.
9. Dialgupgmodems:gupgtog56gKbps,gbandwidthgisgdedicated;gADSL:gupgtog24gMbpsgdowns
treamgandg2.5gMbpsgupstream,gbandwidthgisgdedicated;gHFC,gratesgupgtog42.8gMbpsgand
gupstreamgratesgofgupgtog30.7gMbps,gbandwidthgisgshared.gFTTH:g2-10Mbpsgupload;g10-
20gMbpsgdownload;gbandwidthgisgnotgshared.
10. TheregaregtwogpopulargwirelessgInternetgaccessgtechnologiesgtoday:
a) Wifig(802.11)gIngagwirelessgLAN,gwirelessgusersgtransmit/receivegpacketsgto/fromgangba
segstationg (i.e.,gwirelessgaccessgpoint)gwithingagradiusgofgfewgtensgofgmeters.gThegbasegst
ationgisgtypicallygconnectedgtogthegwiredgInternetgandgthusgservesgtogconnectgwirelessgus
ersgtogthegwiredgnetwork.
b) 3Ggandg4Ggwide-
areagwirelessgaccessgnetworks.gIngthesegsystems,gpacketsgaregtransmittedgovergthegsameg
wirelessginfrastructuregusedgforg cellulargtelephony,g withg the
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baseg stationg thusg beingg managedg byg ag telecommunicationsg provider.g Thisg providesg
wirelessgaccessgtogusersgwithingag radiusgofgtensgofgkilometersgofgthegbasegstation.
11. Atgtimegt0gthegsendingghostgbeginsgtogtransmit.gAtgtimegt1g=gL/R1,gthegsendingghostgcompl
etesgtransmissiongandgthegentiregpacketgisgreceivedgatgthegrouterg(nogpropagationgdelay).g
Becausegthegrouterghasgthegentiregpacketgatgtimegt1,gitgcangbegingtogtransmitgthegpacketgtog
thegreceivingghostgatgtimegt1.gAtgtimegt2g=gt1g+gL/R2,gthegroutergcompletesgtransmissionga
ndgthegentiregpacketgisgreceivedgatgthegreceivingghostg(again,gnogpropagationgdelay).gThu
s,gthegend-to-endgdelaygisg L/R1g +gL/R2.
12. Agcircuit-switchedgnetworkgcangguaranteegagcertaingamountgofgend-to-
endgbandwidthgforgthegdurationgofgagcall.gMostgpacket-
switchedgnetworksgtodayg(includinggthegInternet)gcannotgmakeganygend-to-
endgguaranteesgforgbandwidth.gFDMgrequiresgsophisticatedganalogghardwaregtogshiftgsig
nalgintogappropriategfrequencygbands.
13. a)g 2gusersgcangbegsupportedgbecausegeachgusergrequiresghalfgofgtheglinkgbandwidth.
b) Sincegeachgusergrequiresg1Mbpsgwhengtransmitting,gifgtwogorgfewergusersgtransmitgsi
multaneously,gagmaximumgofg2Mbpsgwillgbegrequired.gSincegthegavailablegbandwidt
hgofgthegsharedglinkgisg2Mbps,gtheregwillgbegnogqueuinggdelaygbeforegtheglink.gWhere
as,gifgthreegusersgtransmitgsimultaneously,g theg bandwidthg requiredgwillgbeg3Mbpsg
whichgisgmoregthangthegavailablegbandwidthgofgthegsharedglink.gIngthisgcase,gtheregwi
llgbegqueuinggdelaygbeforegtheglink.
c) Probabilitygthatgaggivengusergisgtransmittingg=g0.2
3 3
3 gpg (1g g p )
3 3
d) Probabilitygthatgallgthreegusersgaregtransmittinggsimultaneouslyg= g
g
=g(0.2)3g=g0.008.gSincegthegqueueggrowsgwhengallgthegusersgaregtransmitting,gthegfrac
tiongofgtimegduringgwhichgthegqueueggrowsg(whichgisgequalgtogthegprobabilitygthatgall
gthreegusersgaregtransmittinggsimultaneously)gisg0.008.
14. IfgthegtwogISPsgdognotgpeergwithgeachgother,gthengwhengtheygsendgtrafficgtogeachgothergth
eyghavegtogsendgthegtrafficgthroughgagprovidergISPg (intermediary),gtogwhichgtheyghavegt
ogpaygforgcarryinggthegtraffic.gBygpeeringgwithgeachgothergdirectly,gthegtwogISPsgcangred
ucegtheirgpaymentsgtogtheirgprovidergISPs.gAngInternetgExchangegPointsg(IXP)g(typicall
ygingagstandalonegbuildinggwithgitsgowngswitches)gisgagmeetinggpointgwheregmultiplegISP
sgcangconnectgand/orgpeergtogether.gAngISPgearnsgitsgmoneygbygcharginggeachgofgthegtheg
ISPsgthatgconnectgtogthegIXPgagrelativelygsmallgfee,gwhichgmaygdependgong theg amountg of
g trafficg sentg tog org receivedg fromg theg IXP.
15. Google'sgprivategnetworkgconnectsgtogethergallgitsgdatagcenters,gbiggandgsmall.gTrafficgb
etweengthegGooglegdatagcentersgpassesgovergitsgprivategnetworkgrathergthangovergthegpub
licgInternet.gManygofgthesegdatagcentersgareglocatedgin,gorgclosegto,glowergtiergISPs.gTher
efore,gwhengGooglegdeliversgcontentgtogaguser,gitgoftengcangbypassghighergtiergISPs.g Wha
tg motivatesg contentg providersg tog createg theseg networks?g First,g theg content
DownloadedgbygZiadgMysarag(
)
Solution to Computer Networking A Top-
g g g g g
Down Approach (7thEdition)
g g g
Computer Networks (University of Massachusetts Amherst)
g g g g g
StuDocugisgnotgsponsoredgorgendorsedgbyganygcollegegorguniversity
DownloadedgbygZiadgMysarag(
, lOMoAR cPSD| 10861280
Computer Networking: A Top-
g g g
Down Approach,7th Edition
g g g
Solutions to Review Questions and Problems
g g g g g
Version Date: December 2016
g g g
Thisgdocumentgcontainsgthegsolutionsgtogreviewgquestionsgandgproblemsgforgtheg 7thgeditiong
ofgComputergNetworking:gAgTop-
DowngApproachgbygJimgKurosegandgKeithgRoss.gThesegsolutionsgaregbeinggmadegavailablegt
oginstructorsgONLY.gPleasegdogNOTgcopygorgdistributegthisgdocumentgtogothersg(evengotherg
instructors).gPleasegdognotgpostganygsolutionsgongagpublicly-
availablegWebgsite.gWe’llgbeghappygtogprovidegagcopyg(up-to-
date)gofgthisgsolutiongmanualgourselvesgtoganyonegwhogasks.
Acknowledgments:gOvergthegyears,gseveralgstudentsgandgcolleaguesghaveghelpedg usgprepare
gthisgsolutionsgmanual.gSpecialgthanksggoesgtogHongganggZhang,gRakeshgKumar,gPrithulagD
hungel,gandgVijaygAnnapureddy.gAlsogthanksgtogallgthegreadersgwhoghavegmadegsuggestions
gandgcorrectedgerrors.
Allgmaterialg©gcopyrightg1996-2016gbygJ.F.gKurosegandgK.W.gRoss.gAllgrightsgreserved
DownloadedgbygZiadgMysarag(
)
, lOMoAR cPSD| 10861280
Chapter 1 Review Questions
g g g
1. Theregisgnogdifference.gThroughoutgthisgtext,gthegwordsg“host”gandg“endgsystem”gareguse
dginterchangeably.gEndgsystemsgincludegPCs,gworkstations,gWebgservers,gmailgservers,g
PDAs,g Internet-connectedggamegconsoles,getc.
2. FromgWikipedia:gDiplomaticgprotocolgisgcommonlygdescribedgasgagsetgofginternationalgc
ourtesygrules.gThesegwell-establishedgandgtime-
honoredgrulesghavegmadegitgeasiergforgnationsgandgpeoplegtoglivegandgworkgtogether.gPart
gofgprotocolghasgalwaysgbeengthegacknowledgmentgofgtheghierarchicalgstandinggofgallgpre
sent.gProtocolgrulesgaregbasedgongthegprinciplesgofgcivility.
3. Standardsgaregimportantgforgprotocolsgsogthatgpeoplegcangcreategnetworkinggsystemsgand
gproductsgthatginteroperate.
4. 1.gDial-
upgmodemgovergtelephonegline:ghome;g2.gDSLgovergtelephonegline:ghomegorgsmallgoffic
e;g3.gCablegtogHFC:ghome;g4.g100gMbpsgswitchedgEthernet:genterprise;g5.gWifig(802.11):
g homegandgenterprise:g6.g3Ggandg4G:gwide-areagwireless.
5. HFCgbandwidthgisgsharedgamonggthegusers.gOngthegdownstreamgchannel,gallgpacketsgem
anategfromgagsinglegsource,gnamely,gthegheadgend.gThus,gtheregaregnogcollisionsgingthegdo
wnstreamgchannel.
6. IngmostgAmericangcities,gthegcurrentgpossibilitiesginclude:gdial-
up;gDSL;g cablegmodem;gfiber-to-the-home.
7. EthernetgLANsghavegtransmissiongratesgofg10gMbps,g100gMbps,g1gGbpsgandg10gGbps.
8. Today,gEthernetgmostgcommonlygrunsgovergtwisted-
pairgcoppergwire.gItgalsogcangrungovergfibersgopticglinks.
9. Dialgupgmodems:gupgtog56gKbps,gbandwidthgisgdedicated;gADSL:gupgtog24gMbpsgdowns
treamgandg2.5gMbpsgupstream,gbandwidthgisgdedicated;gHFC,gratesgupgtog42.8gMbpsgand
gupstreamgratesgofgupgtog30.7gMbps,gbandwidthgisgshared.gFTTH:g2-10Mbpsgupload;g10-
20gMbpsgdownload;gbandwidthgisgnotgshared.
10. TheregaregtwogpopulargwirelessgInternetgaccessgtechnologiesgtoday:
a) Wifig(802.11)gIngagwirelessgLAN,gwirelessgusersgtransmit/receivegpacketsgto/fromgangba
segstationg (i.e.,gwirelessgaccessgpoint)gwithingagradiusgofgfewgtensgofgmeters.gThegbasegst
ationgisgtypicallygconnectedgtogthegwiredgInternetgandgthusgservesgtogconnectgwirelessgus
ersgtogthegwiredgnetwork.
b) 3Ggandg4Ggwide-
areagwirelessgaccessgnetworks.gIngthesegsystems,gpacketsgaregtransmittedgovergthegsameg
wirelessginfrastructuregusedgforg cellulargtelephony,g withg the
DownloadedgbygZiadgMysarag(
)
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baseg stationg thusg beingg managedg byg ag telecommunicationsg provider.g Thisg providesg
wirelessgaccessgtogusersgwithingag radiusgofgtensgofgkilometersgofgthegbasegstation.
11. Atgtimegt0gthegsendingghostgbeginsgtogtransmit.gAtgtimegt1g=gL/R1,gthegsendingghostgcompl
etesgtransmissiongandgthegentiregpacketgisgreceivedgatgthegrouterg(nogpropagationgdelay).g
Becausegthegrouterghasgthegentiregpacketgatgtimegt1,gitgcangbegingtogtransmitgthegpacketgtog
thegreceivingghostgatgtimegt1.gAtgtimegt2g=gt1g+gL/R2,gthegroutergcompletesgtransmissionga
ndgthegentiregpacketgisgreceivedgatgthegreceivingghostg(again,gnogpropagationgdelay).gThu
s,gthegend-to-endgdelaygisg L/R1g +gL/R2.
12. Agcircuit-switchedgnetworkgcangguaranteegagcertaingamountgofgend-to-
endgbandwidthgforgthegdurationgofgagcall.gMostgpacket-
switchedgnetworksgtodayg(includinggthegInternet)gcannotgmakeganygend-to-
endgguaranteesgforgbandwidth.gFDMgrequiresgsophisticatedganalogghardwaregtogshiftgsig
nalgintogappropriategfrequencygbands.
13. a)g 2gusersgcangbegsupportedgbecausegeachgusergrequiresghalfgofgtheglinkgbandwidth.
b) Sincegeachgusergrequiresg1Mbpsgwhengtransmitting,gifgtwogorgfewergusersgtransmitgsi
multaneously,gagmaximumgofg2Mbpsgwillgbegrequired.gSincegthegavailablegbandwidt
hgofgthegsharedglinkgisg2Mbps,gtheregwillgbegnogqueuinggdelaygbeforegtheglink.gWhere
as,gifgthreegusersgtransmitgsimultaneously,g theg bandwidthg requiredgwillgbeg3Mbpsg
whichgisgmoregthangthegavailablegbandwidthgofgthegsharedglink.gIngthisgcase,gtheregwi
llgbegqueuinggdelaygbeforegtheglink.
c) Probabilitygthatgaggivengusergisgtransmittingg=g0.2
3 3
3 gpg (1g g p )
3 3
d) Probabilitygthatgallgthreegusersgaregtransmittinggsimultaneouslyg= g
g
=g(0.2)3g=g0.008.gSincegthegqueueggrowsgwhengallgthegusersgaregtransmitting,gthegfrac
tiongofgtimegduringgwhichgthegqueueggrowsg(whichgisgequalgtogthegprobabilitygthatgall
gthreegusersgaregtransmittinggsimultaneously)gisg0.008.
14. IfgthegtwogISPsgdognotgpeergwithgeachgother,gthengwhengtheygsendgtrafficgtogeachgothergth
eyghavegtogsendgthegtrafficgthroughgagprovidergISPg (intermediary),gtogwhichgtheyghavegt
ogpaygforgcarryinggthegtraffic.gBygpeeringgwithgeachgothergdirectly,gthegtwogISPsgcangred
ucegtheirgpaymentsgtogtheirgprovidergISPs.gAngInternetgExchangegPointsg(IXP)g(typicall
ygingagstandalonegbuildinggwithgitsgowngswitches)gisgagmeetinggpointgwheregmultiplegISP
sgcangconnectgand/orgpeergtogether.gAngISPgearnsgitsgmoneygbygcharginggeachgofgthegtheg
ISPsgthatgconnectgtogthegIXPgagrelativelygsmallgfee,gwhichgmaygdependgong theg amountg of
g trafficg sentg tog org receivedg fromg theg IXP.
15. Google'sgprivategnetworkgconnectsgtogethergallgitsgdatagcenters,gbiggandgsmall.gTrafficgb
etweengthegGooglegdatagcentersgpassesgovergitsgprivategnetworkgrathergthangovergthegpub
licgInternet.gManygofgthesegdatagcentersgareglocatedgin,gorgclosegto,glowergtiergISPs.gTher
efore,gwhengGooglegdeliversgcontentgtogaguser,gitgoftengcangbypassghighergtiergISPs.g Wha
tg motivatesg contentg providersg tog createg theseg networks?g First,g theg content
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