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Telecommunication Networks Assignment SP2 2017

Telecommunication Networks Assignment SP2 2017

Network dimensioning for a large organisation

Thisassignmentisintendedtotestyourabilitytoapplythesimplecomponentsof knowledgegainedthroughoutthecoursetoa“real‐life”problem.Youwillneedtobe abletomakerealisticassumptions,justifythem,andthentranslatethemintothedesign ofyoursystem.

Telecommunication Networks Assignment SP2 2017Pleasenotethatinpracticeeachsetofassumptionsmadebyindividualstudentswillbe unique.Thereisnoonecorrectsetofassumptions,onecorrectmethodtosolveeach problem,oronecorrectanswertothetaskyouwillbeaskedtocarryout.However,to scorewell,youneedtobeabletoprovideconvincingjustificationofyourchoicesof assumptionsaswellasmethodsusedtoproduceadesignthatisconsistentwiththese assumptions.

NotethatforthetelephonelinesdimensioningtasksyoumayhavetolocateanErlangB calculatorthatdoesnothavethelimitationsonthetrafficintensityandnumberof circuits–therearemanycalculatorslikethisavailableonthewww.

Pleaserememberthatthisisanindividualassignmentworkthathastobecarriedout byindividualstudentswithoutexternalhelp.

Also,pleaserememberthatthisisNOTahugetaskthatrequireshundredsofhoursof effortandtensofpagesofreporting.Youcanfinishtheassignmentwithinnomorethan 10‐15hours,andprepareacompletereportnolongerthan6‐10pages.

1. The scenario

ConsideralargeorganisationwithtwobuildingsAandB.BuildingAiswhereallcentral ITfacilities(PABX,VoIPserver,Intranetserver)arelocated.Buildingsareconnectedwith eachotherandwiththeoutsideworldasshowninthefigurebelow.

Thecentralserversinclude,dependingonthescenario,PABX,Intranetwwwandfile servers,mailserveretc.

TheI/Fdenotesinterfaceequipmenttotheconnectinglinkorcircuitgroup.Depending onthescenario,itmightbeaPDHmultiplexinterface,IProuter,etc.

Telecommunication Networks Assignment SP2 2017

Centralservers(PABX,intranet,

email…)

ABandBA

I/F

I/F

BuildingB

To/from outside network

BuildingA

I/F

Interface equipment(routers,

concentrators,PDH circuit group

interface)

Commonassumptions:

1.Allemployeesoftheorganisationhaveatelephoneandcomputerontheir individualdesk.

2.Thereare2000stafflocatedinbuildingA.Thesearethemanagement, administration,marketing,sales,supportetc.staff.Assumethatallofthem generatethesametelephoneanddatatraffic.Duringtheworkingday,they generateandreceivemanyphonecallsto/fromoutsideworldaswellasafew phonecallsto/fromotheremployeesoftheorganisation.However,mostoftheir moderatedatatrafficisinternal(accessingwebapplicationsrunningonthe internalserverandexchanginginternalemails),andonlysmallproportionof datatrafficisexternal(mostlyemails).

3.Thereare3000stafflocatedinbuildingB,allofthememployedinthe engineeringandproductdevelopmentdepartmentsoftheorganisation.Assume thatallofthemgeneratethesametelephoneanddatatraffic.Duringthe workingday,theygenerateandreceiveafewphonecallsto/fromother employeesoftheorganisationaswellasoutsideworld,buttheiruseof telephoneissignificantlylessfrequentasthatofbuildingAemployees.However, inadditiontoamoderateinternaldatatraffic(emailsandaccesstowebbased applicationsrunningontheorganisation’sserver),theygeneratesignificant externaldatatrafficresultingfrombrowsinganddownloadingtechnicaldata, standards,engineering/researchliteratureetc.

4.Assumethatalltelephoneanddatatrafficgeneratedbyemployeesofthe organisationcanbeconsideredPoisson.Thisisacrudeassumption(pleasecheck theslidesonInternettraffic),butnecessaryforsimplicity.

5.Whenconsideringinternaltelephonetraffic,assume(forsimplicity)thatthereis thesamevolumeofinternaltelephonetrafficflowingbetweenanytwo employeesoftheorganisation,regardlessofthedepartmentstheyworkin.For example,thevolumeoftrafficflowingbetweenLizfromengineeringandJames fromadministrationwillbethesameastrafficflowingbetweenNataliefrom marketingandChrisfromproductdevelopment.

2. Your tasks

Task1:

Makerealisticassumptionsastothetrafficgenerationbehaviourofanindividual employee(inaccordancewithassumptions2and3,youneedtodifferentiatebetween employeesfrombuildingAandemployeesfrombuildingBwhenconsideringexternal telephonetrafficanddatatraffic).Inotherwords,assignnumberstothefollowing:

a)Averagearrivalrateofexternaltelephonecallsto/fromeachstaffmember’s

telephoneλiAext andλiBext (forbuildingsAandBrespectively).Assumethatthis includesbothoutgoingandincomingcallsandwillhavethesamevalueforall staffinthesamebuilding.

b)Averagearrivalrateofinternaltelephonecallsto/fromeachstaffmember’s

telephoneλi.Assumethatthisincludesbothoutgoingandincomingcalls.Note thatinaccordancewithassumption5above,thiswillbethesameforall employeesregardlessofthebuildingtheyarelocatedin.

c)Averagecallholdingtime(forsimplicity,assumethesamevalueforallcalls, externalandinternal).

d)Theaverageexternaldownlinkdatatraffic(fileandemaildownloads,webpages)perstaffmemberlocatedinbuildingAinbps(orkbpsorMbps–whateversuits thepurpose).

e)Theaverageexternaldownlinkdatatraffic(fileandemaildownloads,webpages)perstaffmemberlocatedinbuildingBinbps(orkbpsorMbps–whateversuits thepurpose).

f)Theaverageexternaluplinkdatatraffic(emailssent,webpagerequests,TCPACKs)perstaffmemberlocatedinbuildingAinbps(orkbpsorMbps–whatever suitsthepurpose).

g)Theaverageexternaluplinkdatatraffic(emailssent,webpagerequests,TCPACKs)perstaffmemberlocatedinbuildingBinbps(orkbpsorMbps–whatever suitsthepurpose).

h)Theaverageinternaldownlinkdatatraffic(fileandemaildownloads,webpages)perstaffmemberlocatedinbuildingAinbps(orkbpsorMbps–whateversuits thepurpose).

i)Theaverageinternaldownlinkdatatraffic(fileandemaildownloads,webpages)perstaffmemberlocatedinbuildingBinbps(orkbpsorMbps–whateversuits thepurpose).

j)Theaverageinternaluplinkdatatraffic(emailssent,webpagerequests,TCPACKs)perstaffmemberlocatedinbuildingAinbps(orkbpsorMbps–whatever suitsthepurpose).

k)Theaverageinternaluplinkdatatraffic(emailssent,webpagerequests,TCPACKs)perstaffmemberlocatedinbuildingBinbps(orkbpsorMbps–whatever suitsthepurpose).

Providerationaleforeachassumption(i.e.explainbrieflywhyyouconsideritrealistic).

Task2:

Forthistask,onlyconsidertelephonetraffic.Assumethatalltelephonetrafficiscircuit‐ switchedasinthetraditionalPSTN.Therelevantscenarioisillustratedinthefigure below.The“centralservers”becomeaPABX,the“interfaceequipment”atbuildingB becomesatelephonelineconcentratorwithPDHmultiplexequipment,andthe interfaceatbuildingAbecomesPDHmultiplexequipment,asinthefigure.

PABX

ABandBA

I/F

I/F

BuildingB

To/from outside network

BuildingA

I/F

PDH circuit groupinterface

PDH circuit groupinterface

a)GiventheassumptionsmadeinTask1a,b,c,mapthetotaltelephonetraffic flows(inErlangs)ontocircuitgroupA‐Bandtheexternalcircuitgroup.Showthe reasoningleadingtotheansweryougave.

b)Ifwerequirethattheend‐to‐endGoSprobabilityoflossforeachcall(internal andexternal)benogreaterthan0.01(1in100),whataretheGoSprobabilities oflossallowedforeachofthetwogroupsofcircuits?

c)Giventheresultsinaandbabove,whataretherequirednumbersofcircuitsin eachgroup?

Task3:

Forthistask,onlyconsiderdatatrafficasspecifiedinTask1d‐k.Asillustratedinthe figurebelow,the“centralservers”nowbecometheemail/wwwservers,andthe “interfaceequipment”issimplyIProuters.

SERVERS

ABandBA

I/F

I/F

BuildingB

To/from outside network

BuildingA

I/F

routers

router

a)Mapthetotalflowsofdata(inkbpsorMbps)generatedbystaffontothelinks connectingbuildingBwithAandbuildingAwithoutsideworld.Pleaseassume thatbothlinksarepartofWAN(leasedfromexternalproviders),notpartofthe organisation’sEthernet.Asaconsequence,foreachlinkyouhavetostate separatelythedownlinkanduplinktraffic.Providerationale(explanation)for youranswer.

b)Giventhetrafficflowsobtainedinaabove,statethedataratecapacity(inMbps) requiredforeachlink(separatelyinthedownlinkanduplinkdirections),under theconditionthataveragepacketdelayforeachlinkcannotexceed2ms. Assumethattheinternaldatatransfersbetweenservers,hostsandrouters locatedinthesamebuildingincurnegligibledelay,andthattheprocessingdelay atserversandroutersisalsonegligible. Note:youmayneedtomakearealistic assumptionregardingtheaveragepacketlength(why?)

c)CalculatethebuffersizesrequiredonthelinkABandthelinkBAtoensure thatthepacketlossinnomorethan1in2000.

Task4:

Forthistask,assumethatalltelephonyneedsoftheorganisationareservedwiththe VoIPsolution.AssumethattheVoIPcodecrateis64kbps.Assumethatthemodem transmitsdataonlywhenthereisatalkspurt,andthatitdoesnottransmitanything duringthesilenceperiod.Assumetheaveragetalkspurtdurationof0.6sandthe averagesilencedurationof0.4s,andthatinatypicalphonecall50%oftalkspurtsare transmittedinonedirectionand50%intheother(i.e.thatthetwopeopleinvolvedin thecallwilltalk,onaverage,forthesameamountoftime).Thisresultsinthesymmetry ofdownlinkanduplinktrafficloadsincurredbyaVoIPcall.

a)CalculatetheadditionalVoIPdatatraffic(inkbpsorMbps)loadingeachofthe twolinks(external,A‐B)ineach(uplinkanddownlink)direction.

b)Giventhatalltrafficintheorganisationisnowdatatraffic,calculatethetotal datatrafficforeachlinkineachdirection(i.e.addtheVoIPtraffictothedata trafficresultingfromTask3a).

c)WilltheadditionofVoIPtraffictotheremainingdatatrafficmakesignificant differencetothedimensioningofthedatalinks?Justifyyouranswer.

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