lOMoAR cPSD| 10861280
Solution to Computer Networking A Top-
i i i i i
Down Approach (7thEdition)
i i i
StuDocuiisinotisponsoredioriendorsedibyianyicollegeioriuniversity
DownloadedibyiZiadiMysarai()
, lOMoAR cPSD| 10861280
Computer Networking: A Top-
i i i
Down Approach,7th Edition
i i i
Solutions to Review Questions and Problems
i i i i i
Version Date: December 2016
i i i
Thisidocumenticontainsitheisolutionsitoireviewiquestionsiandiproblemsiforithei 7thieditioniofi
ComputeriNetworking:iAiTop-
DowniApproachibyiJimiKuroseiandiKeithiRoss.iTheseisolutionsiareibeingimadeiavailableitoii
nstructorsiONLY.iPleaseidoiNOTicopyioridistributeithisidocumentitoiothersi(eveniotheriinstru
ctors).iPleaseidoinotipostianyisolutionsioniaipublicly-
availableiWebisite.iWe’llibeihappyitoiprovideiaicopyi(up-to-
date)iofithisisolutionimanualiourselvesitoianyoneiwhoiasks.
Acknowledgments:iOveritheiyears,iseveralistudentsiandicolleaguesihaveihelpedi usiprepareith
isisolutionsimanual.iSpecialithanksigoesitoiHonggangiZhang,iRakeshiKumar,iPrithulaiDhung
el,iandiVijayiAnnapureddy.iAlsoithanksitoiallitheireadersiwhoihaveimadeisuggestionsiandicorr
ectedierrors.
Allimateriali©icopyrighti1996-2016ibyiJ.F.iKuroseiandiK.W.iRoss.iAllirightsireserved
DownloadedibyiZiadiMysarai()
, lOMoAR cPSD| 10861280
Chapter 1 Review Questions
i i i
1. Thereiisinoidifference.iThroughoutithisitext,itheiwordsi“host”iandi“endisystem”iareiusedii
nterchangeably.iEndisystemsiincludeiPCs,iworkstations,iWebiservers,imailiservers,iPDA
s,iInternet-connectedigameiconsoles,ietc.
2. FromiWikipedia:iDiplomaticiprotocoliisicommonlyidescribediasiaisetiofiinternationalicou
rtesyirules.iTheseiwell-establishedianditime-
honoredirulesihaveimadeiitieasieriforinationsiandipeopleitoiliveiandiworkitogether.iPartiofi
protocolihasialwaysibeenitheiacknowledgmentiofitheihierarchicalistandingiofiallipresent.i
Protocolirulesiareibasedionitheiprinciplesioficivility.
3. Standardsiareiimportantiforiprotocolsisoithatipeopleicanicreateinetworkingisystemsiandipr
oductsithatiinteroperate.
4. 1.iDial-
upimodemioveritelephoneiline:ihome;i2.iDSLioveritelephoneiline:ihomeiorismallioffice;i3.i
CableitoiHFC:ihome;i4.i100iMbpsiswitchediEthernet:ienterprise;i5.iWifii(802.11):i homei
andienterprise:i6.i3Giandi4G:iwide-areaiwireless.
5. HFCibandwidthiisisharediamongitheiusers.iOnitheidownstreamichannel,iallipacketsieman
ateifromiaisingleisource,inamely,itheiheadiend.iThus,ithereiareinoicollisionsiinitheidownstr
eamichannel.
6. InimostiAmericanicities,itheicurrentipossibilitiesiinclude:idial-
up;iDSL;i cableimodem;ifiber-to-the-home.
7. EthernetiLANsihaveitransmissioniratesiofi10iMbps,i100iMbps,i1iGbpsiandi10iGbps.
8. Today,iEthernetimosticommonlyirunsioveritwisted-
pairicopperiwire.iItialsoicanirunioverifibersiopticilinks.
9. Dialiupimodems:iupitoi56iKbps,ibandwidthiisidedicated;iADSL:iupitoi24iMbpsidownstrea
miandi2.5iMbpsiupstream,ibandwidthiisidedicated;iHFC,iratesiupitoi42.8iMbpsiandiupstre
amiratesiofiupitoi30.7iMbps,ibandwidthiisishared.iFTTH:i2-10Mbpsiupload;i10-
20iMbpsidownload;ibandwidthiisinotishared.
10. ThereiareitwoipopulariwirelessiInternetiaccessitechnologiesitoday:
a) Wifii(802.11)iIniaiwirelessiLAN,iwirelessiusersitransmit/receiveipacketsito/fromianibasei
stationi (i.e.,iwirelessiaccessipoint)iwithiniairadiusiofifewitensiofimeters.iTheibaseistationii
sitypicallyiconnecteditoitheiwirediInternetiandithusiservesitoiconnectiwirelessiusersitoithei
wiredinetwork.
b) 3Giandi4Giwide-
areaiwirelessiaccessinetworks.iInitheseisystems,ipacketsiareitransmittedioveritheisamei wir
elessiinfrastructureiusedi fori cellularitelephony,i withi the
DownloadedibyiZiadiMysarai()
, lOMoAR cPSD| 10861280
basei stationi thusi beingi managedi byi ai telecommunicationsi provider.i Thisi providesiwir
elessiaccessitoiusersiwithiniai radiusiofitensiofikilometersiofitheibaseistation.
11. Atitimeit0itheisendingihostibeginsitoitransmit.iAtitimeit1i=iL/R1,itheisendingihosticompletes
itransmissionianditheientireipacketiisireceivediatitheirouteri(noipropagationidelay).i Becaus
eitheirouterihasitheientireipacketiatitimeit1,iiticanibeginitoitransmititheipacketitoitheireceivin
gihostiatitimeit1.iAtitimeit2i=it1i+iL/R2,itheiroutericompletesitransmissionianditheientireipac
ketiisireceivediatitheireceivingihosti(again,inoipropagationidelay).iThus,itheiend-to-
endidelayiisi L/R1i +iL/R2.
12. Aicircuit-switchedinetworkicaniguaranteeiaicertainiamountiofiend-to-
endibandwidthiforitheidurationiofiaicall.iMostipacket-
switchedinetworksitodayi(includingitheiInternet)icannotimakeianyiend-to-
endiguaranteesiforibandwidth.iFDMirequiresisophisticatedianalogihardwareitoishiftisigna
liintoiappropriateifrequencyibands.
13. a)i 2iusersicanibeisupportedibecauseieachiuserirequiresihalfiofitheilinkibandwidth.
b) Sinceieachiuserirequiresi1Mbpsiwhenitransmitting,iifitwoiorifeweriusersitransmitisimu
ltaneously,iaimaximumiofi2Mbpsiwillibeirequired.iSinceitheiavailableibandwidthiofit
heisharedilinkiisi2Mbps,ithereiwillibeinoiqueuingidelayibeforeitheilink.iWhereas,iifithr
eeiusersitransmitisimultaneously,i thei bandwidthi requirediwillibei3Mbpsiwhichiisim
oreithanitheiavailableibandwidthiofitheisharedilink.iInithisicase,ithereiwillibeiqueuingid
elayibeforeitheilink.
c) Probabilityithatiaigiveniuseriisitransmittingi=i0.2
3 3
3 ipi (1i i p )
3 3
d) Probabilityithatiallithreeiusersiareitransmittingisimultaneouslyi= i
i
=i(0.2)3i=i0.008.iSinceitheiqueueigrowsiwheniallitheiusersiareitransmitting,itheifraction
iofitimeiduringiwhichitheiqueueigrowsi(whichiisiequalitoitheiprobabilityithatiallithreeiu
sersiareitransmittingisimultaneously)iisi0.008.
14. IfitheitwoiISPsidoinotipeeriwithieachiother,itheniwhenitheyisenditrafficitoieachiotheritheyih
aveitoisenditheitrafficithroughiaiprovideriISPi (intermediary),itoiwhichitheyihaveitoipayifor
icarryingitheitraffic.i Byipeeringiwithieachiotheridirectly,itheitwoi ISPsicanireduceitheiripay
mentsitoitheiriprovideriISPs.iAniInternetiExchangeiPointsi(IXP)i(typicallyiiniaistandalonei
buildingiwithiitsiowniswitches)iisiaimeetingipointiwhereimultipleiISPsicaniconnectiand/ori
peeritogether.iAniISPiearnsiitsimoneyibyichargingieachiofitheitheiISPsithaticonnectitoitheiI
XPiairelativelyismallifee,iwhichimayidependioni thei amounti ofi traffici senti toi ori receivedi fr
omi thei IXP.
15. Google'siprivateinetworkiconnectsitogetherialliitsidataicenters,ibigiandismall.iTrafficibetw
eenitheiGoogleidataicentersipassesioveriitsiprivateinetworkiratherithanioveritheipubliciInte
rnet.iManyiofitheseidataicentersiareilocatediin,ioricloseito,iloweritieriISPs.iTherefore,iwhen
iGoogleideliversicontentitoiaiuser,iitioftenicanibypassihigheritieri ISPs.i Whati motivatesi co
ntenti providersi toi createi thesei networks?i First,i thei content
DownloadedibyiZiadiMysarai()
Solution to Computer Networking A Top-
i i i i i
Down Approach (7thEdition)
i i i
StuDocuiisinotisponsoredioriendorsedibyianyicollegeioriuniversity
DownloadedibyiZiadiMysarai()
, lOMoAR cPSD| 10861280
Computer Networking: A Top-
i i i
Down Approach,7th Edition
i i i
Solutions to Review Questions and Problems
i i i i i
Version Date: December 2016
i i i
Thisidocumenticontainsitheisolutionsitoireviewiquestionsiandiproblemsiforithei 7thieditioniofi
ComputeriNetworking:iAiTop-
DowniApproachibyiJimiKuroseiandiKeithiRoss.iTheseisolutionsiareibeingimadeiavailableitoii
nstructorsiONLY.iPleaseidoiNOTicopyioridistributeithisidocumentitoiothersi(eveniotheriinstru
ctors).iPleaseidoinotipostianyisolutionsioniaipublicly-
availableiWebisite.iWe’llibeihappyitoiprovideiaicopyi(up-to-
date)iofithisisolutionimanualiourselvesitoianyoneiwhoiasks.
Acknowledgments:iOveritheiyears,iseveralistudentsiandicolleaguesihaveihelpedi usiprepareith
isisolutionsimanual.iSpecialithanksigoesitoiHonggangiZhang,iRakeshiKumar,iPrithulaiDhung
el,iandiVijayiAnnapureddy.iAlsoithanksitoiallitheireadersiwhoihaveimadeisuggestionsiandicorr
ectedierrors.
Allimateriali©icopyrighti1996-2016ibyiJ.F.iKuroseiandiK.W.iRoss.iAllirightsireserved
DownloadedibyiZiadiMysarai()
, lOMoAR cPSD| 10861280
Chapter 1 Review Questions
i i i
1. Thereiisinoidifference.iThroughoutithisitext,itheiwordsi“host”iandi“endisystem”iareiusedii
nterchangeably.iEndisystemsiincludeiPCs,iworkstations,iWebiservers,imailiservers,iPDA
s,iInternet-connectedigameiconsoles,ietc.
2. FromiWikipedia:iDiplomaticiprotocoliisicommonlyidescribediasiaisetiofiinternationalicou
rtesyirules.iTheseiwell-establishedianditime-
honoredirulesihaveimadeiitieasieriforinationsiandipeopleitoiliveiandiworkitogether.iPartiofi
protocolihasialwaysibeenitheiacknowledgmentiofitheihierarchicalistandingiofiallipresent.i
Protocolirulesiareibasedionitheiprinciplesioficivility.
3. Standardsiareiimportantiforiprotocolsisoithatipeopleicanicreateinetworkingisystemsiandipr
oductsithatiinteroperate.
4. 1.iDial-
upimodemioveritelephoneiline:ihome;i2.iDSLioveritelephoneiline:ihomeiorismallioffice;i3.i
CableitoiHFC:ihome;i4.i100iMbpsiswitchediEthernet:ienterprise;i5.iWifii(802.11):i homei
andienterprise:i6.i3Giandi4G:iwide-areaiwireless.
5. HFCibandwidthiisisharediamongitheiusers.iOnitheidownstreamichannel,iallipacketsieman
ateifromiaisingleisource,inamely,itheiheadiend.iThus,ithereiareinoicollisionsiinitheidownstr
eamichannel.
6. InimostiAmericanicities,itheicurrentipossibilitiesiinclude:idial-
up;iDSL;i cableimodem;ifiber-to-the-home.
7. EthernetiLANsihaveitransmissioniratesiofi10iMbps,i100iMbps,i1iGbpsiandi10iGbps.
8. Today,iEthernetimosticommonlyirunsioveritwisted-
pairicopperiwire.iItialsoicanirunioverifibersiopticilinks.
9. Dialiupimodems:iupitoi56iKbps,ibandwidthiisidedicated;iADSL:iupitoi24iMbpsidownstrea
miandi2.5iMbpsiupstream,ibandwidthiisidedicated;iHFC,iratesiupitoi42.8iMbpsiandiupstre
amiratesiofiupitoi30.7iMbps,ibandwidthiisishared.iFTTH:i2-10Mbpsiupload;i10-
20iMbpsidownload;ibandwidthiisinotishared.
10. ThereiareitwoipopulariwirelessiInternetiaccessitechnologiesitoday:
a) Wifii(802.11)iIniaiwirelessiLAN,iwirelessiusersitransmit/receiveipacketsito/fromianibasei
stationi (i.e.,iwirelessiaccessipoint)iwithiniairadiusiofifewitensiofimeters.iTheibaseistationii
sitypicallyiconnecteditoitheiwirediInternetiandithusiservesitoiconnectiwirelessiusersitoithei
wiredinetwork.
b) 3Giandi4Giwide-
areaiwirelessiaccessinetworks.iInitheseisystems,ipacketsiareitransmittedioveritheisamei wir
elessiinfrastructureiusedi fori cellularitelephony,i withi the
DownloadedibyiZiadiMysarai()
, lOMoAR cPSD| 10861280
basei stationi thusi beingi managedi byi ai telecommunicationsi provider.i Thisi providesiwir
elessiaccessitoiusersiwithiniai radiusiofitensiofikilometersiofitheibaseistation.
11. Atitimeit0itheisendingihostibeginsitoitransmit.iAtitimeit1i=iL/R1,itheisendingihosticompletes
itransmissionianditheientireipacketiisireceivediatitheirouteri(noipropagationidelay).i Becaus
eitheirouterihasitheientireipacketiatitimeit1,iiticanibeginitoitransmititheipacketitoitheireceivin
gihostiatitimeit1.iAtitimeit2i=it1i+iL/R2,itheiroutericompletesitransmissionianditheientireipac
ketiisireceivediatitheireceivingihosti(again,inoipropagationidelay).iThus,itheiend-to-
endidelayiisi L/R1i +iL/R2.
12. Aicircuit-switchedinetworkicaniguaranteeiaicertainiamountiofiend-to-
endibandwidthiforitheidurationiofiaicall.iMostipacket-
switchedinetworksitodayi(includingitheiInternet)icannotimakeianyiend-to-
endiguaranteesiforibandwidth.iFDMirequiresisophisticatedianalogihardwareitoishiftisigna
liintoiappropriateifrequencyibands.
13. a)i 2iusersicanibeisupportedibecauseieachiuserirequiresihalfiofitheilinkibandwidth.
b) Sinceieachiuserirequiresi1Mbpsiwhenitransmitting,iifitwoiorifeweriusersitransmitisimu
ltaneously,iaimaximumiofi2Mbpsiwillibeirequired.iSinceitheiavailableibandwidthiofit
heisharedilinkiisi2Mbps,ithereiwillibeinoiqueuingidelayibeforeitheilink.iWhereas,iifithr
eeiusersitransmitisimultaneously,i thei bandwidthi requirediwillibei3Mbpsiwhichiisim
oreithanitheiavailableibandwidthiofitheisharedilink.iInithisicase,ithereiwillibeiqueuingid
elayibeforeitheilink.
c) Probabilityithatiaigiveniuseriisitransmittingi=i0.2
3 3
3 ipi (1i i p )
3 3
d) Probabilityithatiallithreeiusersiareitransmittingisimultaneouslyi= i
i
=i(0.2)3i=i0.008.iSinceitheiqueueigrowsiwheniallitheiusersiareitransmitting,itheifraction
iofitimeiduringiwhichitheiqueueigrowsi(whichiisiequalitoitheiprobabilityithatiallithreeiu
sersiareitransmittingisimultaneously)iisi0.008.
14. IfitheitwoiISPsidoinotipeeriwithieachiother,itheniwhenitheyisenditrafficitoieachiotheritheyih
aveitoisenditheitrafficithroughiaiprovideriISPi (intermediary),itoiwhichitheyihaveitoipayifor
icarryingitheitraffic.i Byipeeringiwithieachiotheridirectly,itheitwoi ISPsicanireduceitheiripay
mentsitoitheiriprovideriISPs.iAniInternetiExchangeiPointsi(IXP)i(typicallyiiniaistandalonei
buildingiwithiitsiowniswitches)iisiaimeetingipointiwhereimultipleiISPsicaniconnectiand/ori
peeritogether.iAniISPiearnsiitsimoneyibyichargingieachiofitheitheiISPsithaticonnectitoitheiI
XPiairelativelyismallifee,iwhichimayidependioni thei amounti ofi traffici senti toi ori receivedi fr
omi thei IXP.
15. Google'siprivateinetworkiconnectsitogetherialliitsidataicenters,ibigiandismall.iTrafficibetw
eenitheiGoogleidataicentersipassesioveriitsiprivateinetworkiratherithanioveritheipubliciInte
rnet.iManyiofitheseidataicentersiareilocatediin,ioricloseito,iloweritieriISPs.iTherefore,iwhen
iGoogleideliversicontentitoiaiuser,iitioftenicanibypassihigheritieri ISPs.i Whati motivatesi co
ntenti providersi toi createi thesei networks?i First,i thei content
DownloadedibyiZiadiMysarai()
