Solutions to Chapter 1 - Communication Networks

9/8/2015 SolutionstoChapter1CommunicationNetworks

http://www.ee.ryerson.ca/~courses/cn8800/solutions/Ch1.html 1/10

SolutionstoChapter1

1a.Describethestepbystepprocedurethatisinvolvedfromthetimeyoudepositaletterinamailboxtothetimetheletterisdeliveredtoitsdestination.Whatroledonames,addressesandmailcodes(suchasZIPcodesorpostalcodes)play?Howmighttheletterberoutedtoitsdestination?Towhatextentcantheprocessbeautomated?

Solution:

Thestepsinvolvedinmailingaletterare:

1. Theletterisdepositedinmailbox.2. Theletterispickedupbypostalemployeeandplacedinsack.3. Theletteristakentoasortingstation,whereitissortedaccordingtodestination,asdeterminedbythemailcodeand

groupedwithotherletterswiththesamedestinationmailcode.(Ifthereisnomailcode,thenitisdeterminedbythelargestgeographicalunit,forexample,country(ifspecified),otherwisestate(ifspecified),otherwisecity(ifspecified).)

4. Theletterisshippedtothepostofficethathandlesthemailforthespecificmailcode(orcountryorcity).5. Theletteristhensortedbystreetaddress.6. Theletterispickedupatthepostofficebythepostalworkerresponsiblefordeliveringtothespecifiedaddress.7. Theletterisdeliveredaccordingtothenumberandstreet.

Thenameisnotreallyused,unlessthestreetaddressismissingorincorrect.Thenthenamemightbeusedtodeterminewheretheletterbelongs.(Unlessofcoursetheletterisbeingsenttoasmalltown,wheremostinhabitantsareknowntothepostalworker.)

Themaildeliveryprocesscanbeautomatedbyusingopticalrecognitiononthemailcode.Thelettercanthenbesortedandroutedtothedestinationpostalstation,andeventothedestinationneighborhood,dependingontheamountofgeographicaldetailbuiltintothemailcode.

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1b.Repeatpart(a)foranemailmessage.Atthispoint,youmayhavetoconjecturedifferentapproachesaboutwhatgoesoninsidethecomputernetwork.

Solution:

Thestepsinvolvedinemailingamessageare:

1. Themessageissentelectronicallybyclicking'Send'.(InChapter2weseethattheSimpleMailTransferProtocol(SMTP)isusedtodothis.)

2. Themailproviderofthesendersendsarequesttoanameserverforthenetworkaddressofthemailproviderortherecipient.Themailproviderisdeterminedbytheinformationfollowingthe@symbol.

3. Ifthemailproviderfindsanetworkaddressoftherecipient'smailprovider,thenitsendsthemessagetothataddressintheemailaddress.

4. Uponreceiptofthemessagethemailprovidereitherinformstherecipientautomaticallythatthereismailorwaitsuntilmailisrequestedbytherecipient,dependingonhowthemailserviceissetup.Therecipientisdeterminedbytheinformationbeforethe@symbol.

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1c.Aretheproceduresinparts(a)and(b)connectionorientedorconnectionless?

Solution:

Thetransferserviceoflettersinapostalsystemisconnectionless.Usersdonotsetupconnectionspriortothetransferofeachletter.(Notehoweverthatthepostalsystemmayhaveregularlyscheduledshipmentsofbundlesofmailfromcitytocity,becausethevolumeofmailbetweencitiesispredictable.Theseregularshipmentscanbeviewedasprearranged"connections.")

Emailtransferisalsoaconnectionlessserviceinthattheuserdoesnotsetupendtoendconnectionstosendamessage.WewillseeinChapter2,however,thatemailprotocolsuseconnectionorientedprocedurestoexchangemessages.

NOTE:Forparts(a)and(b)otherstepbystepproceduresarepossible.

2a.Describewhatstepbystepproceduremightbeinvolvedinsidethenetworkinmakingatelephoneconnection.

Solution:

1. Thetelephonenumberspecifiesan"address"wherethereceiverislocated.IntheNorthAmericantelephonenumberingsystemthefirstthreedigitsaretheareacodewhichspecifiesthemaingeographicalregionofthereceiverthenextthreedigitsspecifyaparticulartelephoneofficeintheNorthAmericannetwork.Thefinalfourdigitsidentifytheparticularlocationofthereceiver.



2. Whenatelephonenumberisdialedequipmentattheotherendofthetelephonelineusesthesequenceofdialednumberstodeterminearouteacrossthetelephonenetworkfromthecalloriginatingphonetothedestinationphone.Acircuitisestablishedbetweentheoriginatinganddestinationphonealongtheidentifiedroute.

3. Aringingtoneisthenappliedatthedestinationtoindicatethatthereisanincomingcall.Ifthedestinationparty(aperson,anansweringmachine,orsomeotherdevice)isreadytoanswer,thecalliscompletedthroughtheliftingofthephonesetorsomeequivalentaction.ThesettingupoftelephonecallsisdiscussedinChapter4.

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2b.Nowconsiderapersonalcommunicationservicethatprovidesauserwithapersonaltelephonenumber.Whenthenumberisdialed,thenetworkestablishesaconnectiontowherevertheuserislocatedatthegiventime.Whatfunctionsmustthenetworknowperforminordertoimplementthisservice?

Solution:

1. Thekeydifferencehereisthatthepersonaltelephonenumberisnottiedtoaspecificlocation.Insteadthepersonalnumberisassociatedwithoneormorepiecesofequipment,forexample,acellphone,thatcanrequestservicefromvariouspointsinthenetwork.Thisnecessitatesthetranslationofthepersonaltelephonenumbertoanumberthatcorrespondstoaspecificlocationinthenetworkatagiventime.

2. Whenthetelephonenumberisdialed,amessagerequestingaconnectionsetupissenttothe"home"locationofthepersonalnumber.

3. Thehomelocationmustsomehowbeabletoredirecttheconnectionsetupprocesstothecurrentlocationoftheuser.Forexample,theusermayregisteroneormoreforwarding"addresses"towhichcallsaretoberedirected.Eachpossibleaddressistried,oneatatimeorallatonce,untilthedestinationequipmentislocated.Incellulartelephony,forexample,requestsforconnectionstoagivenmobiletelephonearebroadcastoverspecificchannels.

4. Oncethelocationofthedestinationisidentifiedaconnectionisestablished.

3.Explainhowthetelephonenetworkmightmodifythewaycallsarehandledtoprovidethefollowingservices:

Solutionsfollowquestions:

a. CallDisplay:thenumberand/ornameofthecallingpartyislistedonascreenbeforethecallisanswered.

Alongwiththerequestforconnectionsetup,thesystemsendsidentifyinginformationregardingtheoriginator'sphone.

b. CallWaiting:aspecialsoundisheardwhenthecalledpartyisonthelineandanotheruseristryingtoreachthecalledparty.

Whenasecondcallertriestoaccessabusyline,thesystemappliesanaudiblesound,forexample,a"beep"oratone,tothevoicesignalthatisbeingsenttothecalledparty.Thetonealertsthecalledpartythatthereisanincomingcallandprovidesthechoiceofansweringthesecondcallwithoutdisconnectingthefirstcall.

c. CallAnswer:ifthecalledpartyisbusyorafterthephoneringsaprescribednumberoftimes,thenetworkgivesthecallertheoptionofleavingavoicemessage.

Ifthecallisnotansweredaftersomanyrings,thesystemsestablishesaconnectiontoanothernumber(thatis,forwardsthecall)thatisassociatedwiththeansweringsystem.Thecallisthenautomaticallyansweredbyanansweringsystem.

d. ThreeWayCalling:allowsausertotalkwithtwootherpeopleatthesametime.

Aftertheestablishmentofacallbetweentwoparties,thecallercanthenindicatetothetelephonesystemthatheorshewantstocallathirdparty.Withoutdisconnectingthefirstpair,thesystemsetsupaconnectiontothesecondcalledparty,andonceestablished,transmitsbothconversationstoallpartiessimultaneously.Specialequipmentisrequiredtocombineanddistributethevoicesignalsofthethreeparties.



4a.Supposethattheletterinproblem1issentbyfax.Isthismodeofcommunicationsconnectionlessorconnectionoriented?Realtimeornonrealtime?

Solution:

Inordertosendtheletterbyfax,atelephoneconnectionmustfirstbeestablished.Thereforethemodeofcommunicationsisconnectionoriented.Thetransferofinformationacrossthenetworkoccursinrealtime.

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4b.Repeatpart(a)ifavoicemailmessageisleftatagiventelephone.

Solution:

Again,theprocessofleavingavoicemailmessageisconnectionoriented,sincetheremustbeanendtoendconnectionbetweenthecallerandthereceiverwiththeansweringservice.Theleavingofvoicemailisalsodoneinrealtime.However,themodeofcommunicationbetweenthepersonthatleavesthevoicemailandthepersonthatlistenstothevoicemailisconnectionlessandnonrealtime.Thepeopleinvolveddonotneedtoestablishasimultaneousconnectionwitheachotherinordertocommunicatealso,theyrecordandlistentothemessagesatdifferenttimes.

5.Supposethatnetworkaddressesarescarce,soaddressesareassignedsothattheyarenotgloballyuniqueinparticularsupposethatthesameblockofaddressesmaybeassignedtodifferentorganizations.Howcantheorganizationsmakeuseoftheseaddresses?Canusersfromtwosuchorganizationscommunicatewitheachother?

Solution:

Tomaketheexampleconcretesupposethattwoorganizationsareassignedthesamesetoftelephonenumbers.Clearly,userswithineachorganizationcancommunicatewitheachotheraslongastheyhaveauniqueaddresswithintheorganization.However,communicationsoutsideanorganizationposesaproblemsinceanygivenaddressisnolongeruniqueacrossmultipleorganizations.

Apossibleapproachtoenablingcommunicationsbetweenusersindifferentorganizationsistouseatwostepprocedureasfollows.Eachorganizationhasaspecialgatewaytocommunicateoutsidetheorganization.Internaluserscontactthegatewaytoestablishcallstootherorganizations.Gatewayshaveprocedurestoestablishconnectionswitheachother.Thisenablesgatewaystoestablishconnectionsbetweentheirinternalusersandusersinothernetworks.

6.Explainthesimilaritybetweenthedomainnamesystemandthetelephonedirectoryservice.

Solution:

Bothsystemsareusedtotranslatebetweennamesandnumbers:peoplenamestotelephonenumbersinthecaseoftelephonedirectoriesnetworknamestoIPaddressesinthecaseofDNS.Inbothcases,thetranslationisfromsomethingthatiseasytoremember,thatis,names,tosomethingthatishardertoremember,numbers.

7.ConsidertheNorthAmericantelephonenumberingplandiscussedinthechapter.Couldthisnumberingplanbeusedtoroutepacketsamongusersconnectedtothetelephonenetwork?

Solution:

Yes,ifeachdestinationuseriscompletelyspecifiedbythenumber.Theareacodewouldspecifythegeneralgeographicalareatheprefixwouldidentifythetelephoneofficetowhichpacketsshouldbedirectedthesubscriber'snumber(thelastfourdigits)wouldidentifythefinaltelephonelinealongwhichthepacketsaretobedelivered.

8a.Describethesimilaritiesanddifferencesintheservicesprovidedby(1)amusicprogramdeliveredoverbroadcastradioand(2)musicdeliveredbyadedicatedCDplayer.

Solution:

BothbroadcastradioandadedicatedCDplayerprovideuserswithsimilartypesofinformationandwithalmostthesameperformance.Howeverthebroadcastradiooffersitsserviceinarealtimefashionwithnointeractionwithusers.ACDplayer,ontheotherhand,storesitsinformationonaCDanddeliversitondemand.

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8b.Describehowtheseservicesmightbeprovidedandenhancedbyprovidingthemthroughacommunicationsnetwork.

Solution:

Broadcastradioistypicallytransmittedinrealtimeusingradiowaves"overtheair."Broadcastaudioprogramscanalsobetransmittedoveranycommunicationnetwork.Furthermore,whenstoredinserversthatareattachedtoanetwork,"broadcast"audioprogramscanberetrievedforlisteningatalatertime.IndeedaservercanalsostoreCDaudiomaterialandretrieveitondemand.Ifthenetworkandserveraresufficientlyresponsive,itmayalsobepossibletoprovidetheinteractivityofapersonalCDplayer



throughanetworkbasedservice.

9a.UsetheWorldWideWebtovisitthesitesofseveralmajornewspapers.HowarethesenewspaperschangingthemannerinwhichtheydelivernewsservicesovertheInternet?

Solution:

Traditionally,newspapersdelivernewsinprinted"hardcopy"forminvariouseditionsduringtheday.Theinformationisprimarilyintextform,supplementedbystillpicturesandgraphics.Theinformationinanewspaperisorganizedinseveralsections:mainpage,business,local,sports,classifieds,etc.Someoftherevenueofnewspapersisfromsubscriptions,butmostofthenewspaperrevenueisusuallyfromadvertising.

Inthetraditionalmodel,gettingthenewsfromaparticularnewspaperrequiredgettingthephysicalprintedform.TheWWWandtheInternetallownewspaperstodeliverinformationinelectronicformandatanytimethatauserrequestsit.NewspaperinformationontheWebstillconsistsmostlyoftext,images,andgraphicsthatcanberetrievedanddisplayedreadilybyaWebbrowser.Inmostcases,subscriptionisnotrequiredandadvertisingisdisplayedalongwithnewsinformation.Inordertobecompetitive,newspaperscannolongerworkintermsofeditions,especiallyforlatebreakingnews.Instead,newsitemsareupdatedcontinuouslydayandnight.TheuseofaWebbrowserallowsausertoquicklyfindthenewsitemsofinterest.

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9b.NowvisittheWebsitesofseveralmajortelevisionnetworks.HowaretheychangingthemannerinwhichtheydelivernewsovertheInternet?Whatdifferences,ifany,aretheretotheapproachtakenbytelevisionnetworksandnewspapers?

Solution:

Traditionally,televisionnetworksdelivernewsusingaudio,video,andgraphics,withverylittletext.Newsistraditionallydeliveredinprogramsthatarebroadcastatvarioustimesoftheday.Again,theinformationisorganizedinseveralsections:international,business,sports,entertainment,etc.Therevenueintelevisionnewsisalmostentirelyfromadvertising.TheWWWandtheInternetallowuserstoretrievenewsinformationinelectronicformandatanytime.However,thetransmissionofaudioandvideoovertheInternetposesachallenge,sothisinformationmustbetransmittedincompressedformandinrelativelylowquality.Consequently,moreoftheinformationisprovidedintextform.Thedependenceonaudioandvideoalsorequiredthedevelopmentofapplicationsforthedecompressionanddisplayofsuchinformation.Again,inordertobecompetitive,newsnetworksupdatetheirWebpagescontinuouslydayandnightasnewsdevelops.

10.DiscusstheadvantagesanddisadvantagesoftransmittingfaxmessagesovertheInternetinsteadofthetelephonenetwork.

Solution:

ThecomparisonoffaxtransmissionovertheInternetandoverthetelephonenetworkreflectthedifferencesbetweenemailandtelephonecalls.Thetransmissionofafaxmessageasanattachmenttoanemailmeansthatthetransferofthemessageisnotinrealtimeandthatdeliveryisnotnecessarilyconfirmed.Thetransmissionofafaxmessageoverthetelephonenetwork,ontheotherhand,isrealtimeandisconfirmedwithfairlyhighcertainty.Ontheotherhand,thecostoftransmissionofafaxmessageovertheInternetisveryinexpensiveandisnotdistancesensitive.Thetransmissionoffaxmessagesovertelephonenetworksmayinvolvelongdistancecharges.

11a.Supposethataninteractivevideogameisaccessedoveracommunicationsnetwork.Whatrequirementsareimposedonthenetworkifthenetworkisconnectionoriented?connectionless?

Solution:

Wesupposethatthegameinvolvestheinteractionbetweenaplayerandaserveracrossanetwork.Tosupportaninteractivevideogameoveracommunicationsnetwork,thenetwork,whetherconnectionorientedorconnectionless,mustproviderealtimedeliveryoftheplayer'scommandstotheserver,andoftheserver'sresponsestotheplayer.Withaconnectionorientednetwork,connectionsbetweentheplayerandtheserverstransferthesequenceofcommandsandresponsesthroughoutthegame.Inaconnectionlessnetwork,usercommandsmustbedeliveredtotheotherendontimeinproperordertopreservetherealtimenatureofthegame.

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11b.Repeatpart(a)ifthegameinvolvesseveralplayerslocatedatdifferentsites.

Solution:

Therequirementsonthenetworkdependonhowthegameisimplemented.Inthecentralizedapproachtheplayersinteractthroughacentralserverthatprocessesthecommandsfromalloftheplayers,maintainsaviewofthestateoftheoverallsystem,andissuesappropriateresponsestoalltheplayers.Alternatively,thegamecouldbeimplementedinadecentralizedfashion,whereeachplayerreceivescommandsfromsomeoralloftheplayers,maintainsalocalviewofthesystemstate,andtransmitsresponsestosomeoralloftheplayers.

Inthecentralizedapproach,thenetworkrequirementsareessentiallythesameasthoseinpart(a).Inthedecentralizedapproach,therealtimeresponserequirementmayapplyonlytoasubsetofplayerswhentheyhappentobeinteractingwitheachother.Ifplayersarelocatedatdifferentsites,thenetworkcouldprovidemulticastcapabilitysomessagescanbeexchangedamongtheserverandalltheplayers.



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11c.Repeatpart(b)ifoneormoreoftheplayersisinmotion,forexample,kidsinthebackofthevanduringasummertrip.

Solution:

Ifoneormoreplayersisinmotion,thenthenetworkmustalsobeabletolocateeachmobileplayerandthendeliverandreceiveinformationtoandfromsuchplayer.

12.Discussthesimilaritiesbetweenthefollowingnationaltransportationnetworksandacommunicationsnetwork.Isthetransportationsystemmoresimilartoatelephonenetworkortoapacketnetwork?

a. Railroadnetwork.b. Airlinenetwork.c. Highwaysystem.d. Combinationof(a),(b),and(c).

Solution:

Transportationnetworksaredesignedtotransferpeopleandgoodscommunicationsnetworksaredesignedtotransferinformation.Likecommunicationnetworks,alltransportationsystemsinvolvelinks,intheformofroads,rails,oraircorridors,andswitchingpoints,intheformofstations,airports,andhighwayinterchanges.Addressingandgeographicalnamesareusedintransportationnetworkstoidentifydestinations,androutingofvariousformsisrequiredtodirectgoodstotheirdestinations.Transportationresources,intheformsofcarsorairplanes,aresharedor"multiplexed"amongvariousgoodsthattraversecommonpartsofthenetwork.

a. Railroadnetwork:Goodsorpeoplearriveattrainstationsandareloadedfortransporttospecificplaces.Ticketsare

purchasedforagivendestination,usuallyguaranteeingthattherewillbeaplaceinacarfromthestartingstationallthewaytothedestinationstation.Thisissimilartoestablishingaconnectionacrossatelephonenetwork.Alternatively,apassengermaychoosetopurchaseaticketateachstationalongtheway.Thiscorrespondsmorecloselytoaconnectionlesspacketnetworkmodel.

b. Airlinenetwork:Inthiscasepassengerspurchaseticketsthatguaranteeaseatallthewaytothedestination,evenif

transfersaremadeatintermediateairports.Thisissimilartotheestablishmentofconnectionsacrossatelephonenetwork.

c. Highwaysystems:Trucksorcarsenterthehighwaywithoutmakingreservationsaheadoftimeandwithoutinformingany

centralauthorityoftheirdestinationorroute.Thismodeofoperationcorrespondscloselytotheoperationofaconnectionlesspacketnetwork.

d. Combinationoftransportationsystems:Thecombinationofair,rail,andhighwaytransportationsystemscanandareused

jointlyforthetransferofpeopleandgoods.Eachtransportationsystemisdifferentinhowitisorganizedandhowtransfersareaccomplished.Nevertheless,itispossibletousethesesystemsincombinationtoprovideahigherdegreeofconnectivitybetweensourcesanddestinationsofpeopleandgoods.WewillseethattheInternetplaysarolesimilartothecombinedtransportationsystemsinthattheInternetenablesthetransferofinformationacrossmultipledissimilarnetworksthatmaydifferinhowtheyareorganizedandhowtheyoperate.

13.Inthe1950s,standardcontainersweredevelopedforthetransportationofgoods.Thesestandardcontainerscouldfitonatraincar,onatruck,orinspeciallydesignedcontainerships.Thestandardsizeofthecontainersmakesitpossibletoloadandunloadthemmuchmorequicklythanusingnonstandardcontainersofdifferentsizes.Drawananalogytopacketswitchingcommunicationsnetworks.Inyouransweridentifywhatmightconstituteacontainerandspeculateontheadvantagesthatmaycomefromstandardsizeinformationcontainers.

Solution:

Inapacketswitchingcommunicationsnetwork,thecomponentthatisanalogoustothecontainerisaconstantsizepacket(preferablyofshortlength)thatcanbeusedforthetransportofinformation.Transmissionsystemsofvarioustypescanbedesignedtotransferinformationofthegivenstandardizedsize,muchliketrucks,trains,andshipscanbedesignedtocarrystandardcontainers.Packingandunpackingoffixedsizeunitsissimplerthanforvariablelengthunits.Consequently,itissimplertoschedulethetransferofpacketsacrossswitchesthatuseconstantsizepacketsthanacrossswitchesthatmakeuseofvariablelengthpackets.

14.TherequirementsofworldcommerceledtothebuildingoftheSuezandPanamacanals.Whatanalogoussituationsmightariseincommunicationnetworks?

Solution:



TheSuezandPanamacanalswerebuilttoprovideashorterpathbetweengeographicalareas.Theanalogoussituationarisesincommunicationnetworkswhenthepathbetweentwoareasinthenetworkaretoo"long"eitherintermsofexcessivedelayorinadequatecapacitytotransfergivenvolumesoftraffic.Theadditionofnetworkresourcestoprovideshorterpathsforlowerdelayorwiderpathsforhighercapacitycorrespondstothebuildingofacanal.

15.Twomusicianslocatedindifferentcitieswishtohaveajamsessionoveracommunicationsnetwork.Findthemaximumpossibledistancebetweenthemusiciansiftheyaretointeractinrealtime,inthesenseofexperiencingthesamedelayinhearingeachotherasiftheywere10metersapart.Thespeedofsoundisapproximately330meters/second,andassumethatthenetworktransmitsthesoundatthespeedoflightincable,2.3x108meters/second.

Solution:

Thefirststepistofindthedelayforthesoundwhenthemusiciansare10metersapart:

t10=10/330=30.30milliseconds

d=(2.3x1010)30.30x103)=6969000meters=6969kilometers

Themaximumdistanceisthetimerequiredforarealtime'experience'timesthecabledelay:

16.Thepropagationdelayisthetimethatisrequiredfortheenergyofasignaltopropagatefromonepointtoanother.

a.Findthepropagationdelayforasignaltraversingthefollowingnetworksatthespeedoflightincable(2.3x108meters/second):

acircuitboard10cmaroom10mabuilding100mametropolitanarea100kmacontinent5000kmupanddowntoageostationarysatellite2x36000km

Solution:

Tofindthepropagationdelay,dividedistancebythespeedoflightincable.Thuswehave:

acircuitboardtprop=4.347x1010secondsaroomtprop=4.3478x108secondsabuildingtprop=4.3478x107secondsametropolitanareatprop=4.3478x104secondsacontinenttprop=0.02174secondsupanddowntoageostationarysatellitetprop=0.31304seconds

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16b.Howmanybitsareintransitduringthepropagationdelayintheabovecases,ifbitsareenteringtheabovenetworksatthefollowingtransmissionspeeds:10,000bits/second1megabit/second100megabits/second10gigabits/second.

Solution:

ThenumberofbitsintransitareobtainedbymultiplyingthetransmissionrateRbythepropagation:

Distance(m) 10Kbps 1Mbps 100Mbps 10Gbps

0.14.347x10 4.347x10

0.04347 4.3478

104.3478x10

0.043478 4.3478 434.780

1004.3478x10

0.43478 43.478 4347.800

100000 4.3478 434.78 43478 4.3478x106

5000000 217.4 21740 2174000 2.174x108

72000000 3130.4 313040 31304000 3.1304x109



17.Inproblem16,howlongdoesittaketosendanLbytefileandtoreceivea1byteacknowledgmentback?LetL=1,103,106,and109bytes.

Solution:

Thetotaltimerequiredtosendafileandreceiveanacknowledgmentofitsreceiptisgivenby:

ttotal=Lmessage/R+Lack/R+2*tprop=Lmessage/R+Lack/R+2*d/c

whereLmessageisthemessagelengthinbits,Lackistheacknowledgmentlengthinbits,Risthetransmissionbitrate,disthedistancetraversed,andcisthespeedoflight.

Theaboveequationshowsthattherearetwomainfactorsthatdeterminetotaldelay:

a. MessageandACKtransmissiontime,whichdependsonthemessagelengthandthetransmissionbitrateb. Propagationdelay,whichdependssolelyondistance.

Whenthepropagationdelayissmall,messageandACKtransmissiontimesdeterminethetotaldelay.Ontheotherhand,whenthebitratebecomesverylarge,thepropagationdelayprovidesadelaycomponentthatcannotbereducednomatterhowfastthetransmissionratebecomes.

Thetablesbelowshowthetwomaincomponentsofthetotaldelayinmicroseconds.Themessagetransmissiontimeisshowninredandthepropagationdelayisshowninblue.Theentriesinthetotaldelaytablesarecoloredaccordingtowhichdelaycomponentisdominant.

message+ACKdelay@10kbps

message+ACKdelay@1Mbps

message+ACKdelay@100

Mbpsmessage+ACKdelay@10Gbps

1600 16 0.16 0.0016distance(meters)

2*prop.delay(microseconds) totaldelay@10kbps

totaldelay@1Mbps

totaldelay@100Mbps

totaldelay@10Gbps

0.1 0.00087 1600.00087 16.0008696 0.16087 0.0024710 0.086957 1600.086957 16.0869565 0.246957 0.088557100 0.869565 1600.869565 16.8695652 1.029565 0.871165

100000 869.5652 2469.565217 885.565217 869.7252 869.56685000000 43478.26 45078.26087 43494.2609 43478.42 43478.2672000000 626087 627686.9565 626102.957 626087.1 626087

Table1:Messagelength=1byte




message+ACKdelay@10Gbps

800800 8008 80.08 0.8008distance(meters)

2*prop.delay(microseconds)

totaldelay@10kbps

totaldelay@1Mbps

totaldelay@100Mbps

totaldelay@10Gbps

0.1 0.00087 800800.0009 8008.00087 80.08087 0.8016710 0.086957 800800.087 8008.08696 80.16696 0.887757100 0.869565 800800.8696 8008.86957 80.94957 1.670365

100000 869.5652 801669.5652 8877.56522 949.6452 870.3665000000 43478.26 844278.2609 51486.2609 43558.34 43479.0672000000 626087 1426886.957 634094.957 626167 626087.8

Table2:Messagelength=1000bytes





8.00E+08 8.00E+06 80000.08 800.0008distance 2*prop.delay totaldelay@10 totaldelay@1 totaldelay@100 totaldelay@10



(meters) (microseconds) kbps Mbps Mbps Gbps0.1 0.00087 8.00E+08 8.00E+06 80000.08 800.001710 0.086957 8.00E+08 8.00E+06 80000.17 800.0878100 0.869565 8.00E+08 8.00E+06 80000.95 800.8704

100000 869.5652 8.00E+08 8.00E+06 80869.65 1669.5665000000 43478.26 8.00E+08 8.04E+06 123478.3 44278.2672000000 626087 8.01E+08 8.63E+06 706087 626887






8.00E+11 8.00E+09 8.00E+07 8.00E+05distance(meters)

2*prop.delay(microseconds)

totaldelay@10kbps

totaldelay@1Mbps

totaldelay@100Mbps

totaldelay@10Gbps

0.1 0.00087 8.00E+11 8.00E+09 8.00E+07 8.00E+0510 0.086957 8.00E+11 8.00E+09 8.00E+07 8.00E+05100 0.869565 8.00E+11 8.00E+09 8.00E+07 8.00E+05

100000 869.5652 8.00E+11 8.00E+09 8.00E+07 8.01E+055000000 43478.26 8.00E+11 8.00E+09 8.00E+07 8.43E+0572000000 626087 8.00E+11 8.00E+09 8.06E+07 1.43E+06


18.BYTE,April1995givesthefollowingperformanceandcomplexityofIntelx86processors:

197880860.33DhrystoneMIPs29,000transistors

19822861.2DhrystoneMIPs134,000transistors

19853865DhrystoneMIPs275,000transistors

198948620DhrystoneMIPs1.2milliontransistors

1993Pentium112DhrystoneMIPs3.1milliontransistors

1995P6250+DhrystoneMIPs5.5milliontransistors

Plotperformanceandcomplexityvs.timeinaloglineargraphandcomparetothegrowthratediscussedinthetext.AccesstheIntelwebsite:http://www.intel.comtogetupdatedfiguresontheirprocessors.

Solution:

Dhrystonespersecondisameasureofthenumberoftimesabenchmarkprogramcanberunonagivenprocessor.Theprogramisdesignedtomeasuretheintegerperformanceofaprocessor.Boththeprocessorperformanceandtheprocessorcomplexityplotasapproximatelylinearfunctionsversustimeinalogarithmicscaleplot.



19.UseyourWebbrowsertoaccessasearchengineandretrievethearticle"ABriefHistoryoftheInternet,"byLeiner,Cerf,Clark,Kahn,Kleinrock,Lynch,Postel,Roberts,andWolff.Answerthefollowingquestions:


a. WhowasJ.Licklider,andwhatwashis"GalacticNetwork"concept?

J.Licklider,ofMIT,wasthefirstheadofDARPA.In1962heenvisionedaglobalnetworkofcomputerswhereuserscouldaccessdataorprogramsfromanysite.

b. Whocoinedthetermpacket?

DonaldDaviesandRogerScantleburyofNPL(NationalPhysicsLaboratory)intheUnitedKingdomfirstcoinedtheterm.

c. What(who?)isanIMP?

IMPstandsforInterfaceMessageProcessor.AnIMPisapacketswitchandwasakeycomponentinthedesignoftheARPANET.

d. DidtheARPANETuseNCPorTCP/IP?

TheARPANETusedahosttohostprotocolcalledNetworkControlProtocolorNCP.

e. WaspacketvoiceproposedasanearlyapplicationforInternet?

IntheearlydevelopmentofTCP,workonpacketvoiceinparticularpromptedtheseparationofTCPintotwocomponents:TCPandIP.IPwastoprovideaddressingandforwardingTCPprovidedspecialservicessuchasrecoveryfrompacketlosses(importantforpacketvoice).

f. HowmanynetworksdidtheinitialIPaddressprovidefor?

TheinitialIPaddressingschemeprovidedfor256networks.

20.UseyourWebbrowsertoaccessasearchengineandretrievethefollowingpresentationfromtheCM97conference:"TheFollyLawsofPredictions1.0"byGordonBell.Answerthefollowingquestions:


a. Atwhatratehaveprocessing,storage,andbackbonetechnologiesimprovedfrom1950to2000?Howdoesthisratecomparetoadvancesintelephony?

Processing,storage,andbackbonetechnologieshaveimprovedatannualratesofbetween20%and40%.Telephonyhasadvancedatarateof17%.

b. WhatisMoore'sLaw?



Microelectronictechnologiesimprovebyafactorof4every3years.

c. What'sthepointofmakingpredictions?

Toprovideavisionandchallengeforthefuture.

d. Whatisthedifficultyinanticipatingtrendsthathaveexponentialgrowth?

Thetroublewithexponentialgrowthisthat"youcan'tseethemcoming!"Atanearlystage,thetrendisnotvisibleatalatestagethetrendisunmistakable.

e. WhowasVannevarBushandwhyishefamous?

VannevarBushpositedthe"memex"in1945thatinasenseprovidedthevisionfortheWorldWideWeb.

f. Whatisthesizeinbytesofeachframeinthispresentation?Whatisthesizeinbytesoftheaudioclipforatypicalframe?Whatisthesizeofthevideoclipforatypicalscene?

Thegraphicsonlypresentationisapproximately1MBthegraphicsandaudiopresentationis7MBthevideopresentationfor100kbpsis14MB.

21.UseyourWebbrowsertoaccesscnn.comandplayanewsvideoclip.SpeculateabouthowtheinformationisbeingtransportedovertheInternet.Howdoesthequalityoftheaudioandvideocomparetothatofbroadcastorcabletelevision?

Solution:

ThevideoinformationissentovertheInternet,soapacketmodeofinformationtransferisused.ThevideosignalisplacedinastreamofpacketsthatissentfromthevideoservertothePC.AsteadystreamofvideoinformationneedstobesuppliedtothevideoplayerapplicationinthePC.Forthisreasontheplayerfirstbuffersacertainamountofvideoinformationinordertoavoidrunningoutofmaterialtoplayoutduringperiodswhenthepacketsencountercongestionandexperienceexcessivedelay.TheInternetisstillsubjecttocongestionandsopacketsaredelayedandlostresultinginpooraudioandvideoquality.

22.TheofficialstandardsoftheInternetcommunityarepublishedasaRequestforComment,orRFC.UseyourWebbrowsertoaccesstheIETFwebpage,http://www.ietf.org.


a. FindandretrievetheRFCtitled"InternetOfficialProtocolStandards".ThisRFChadnumber2400atthetimeofwriting.ThisRFCgivesthestateofstandardizationofthevariousInternetprotocols.Whatisthestateandstandardnumberofthefollowingprotocols:IP,UDP,TCP,

TELNET,FTP,DNS,ARP?

IPstandard,#5UDPstandard,#6TCPstandard,#7TELNETstandard,#8FTPstandard,#9DNSstandard,#13ARPstandard,#37

Note:RFC2400isnowRFC2600,andalsoStandard1,asofMarch2000.

b. FindandretrievetheRFCtitled"AssignedNumbers".ThisRFC,number1700atthetimeofwriting,containsallthenumbersandconstantsthatareusedinInternetprotocols.WhataretheportnumbersforTelnet,ftp,andhttp?

TelnetPort23FTPPorts20/21HTTPPort80.

Documents

Solutions to Chapter 1 - Communication Networks