英文文獻(xiàn)-科技類(lèi)-原文及翻譯-(電子-電氣-自動(dòng)化-通信)1

1、PAGE PAGE 12外文文獻(xiàn)原文On the deployment of VoIP in Ethernet networks: methoddologyy and case studyyAbstracctDeployiing IPP teleephonyy or vvoice over IP (VVoIP) is a majorr and challlenginng tassk forr dataa netwwork rresearrcherss and desiggners. Thiss papeer outtliness guiddelinees andd a sttep-byy-st

2、epp methhodoloogy onn how VoIP can bbe depployedd succcessfuully. The mmethoddologyy can be ussed too asseess thhe suppport and rreadinness oof an existting nnetworrk. Prrior tto thee purcchase and ddeployyment of VooIP eqquipmeent, tthe meethodoology prediicts tthe nuumber of VooIP caalls tthat cca

3、n bee susttainedd by aan exiistingg netwwork wwhile satissfyingg QoS requiiremennts off all netwoork seervicees andd leavving aadequaate caapacitty forr futuure grrowth. As aa casee studdy, wee applly thee methhodoloogy stteps oon a ttypicaal nettwork of a smalll enteerprisse. Wee utillize bboth aan

4、alyssis annd simmulatiion too inveestigaate thhroughhput aand deelay bboundss. Ourr anallysis is baased oon queeuing theorry, annd OPNNET iss usedd for simullationn. Ressults obtaiined ffrom aanalyssis annd simmulatiion arre in line and ggive aa closse mattch. IIn addditionn, thee papeer disscussees

5、 manny dessign aand enngineeering issuees. Thhese iissuess incllude ccharaccterisstics of VooIP trrafficc and QoS rrequirrementts, VooIP fllow annd calll disstribuution, defiining futurre groowth ccapaciity, aand meeasureement and iimpactt of bbackgrround trafffic. Keywordds: Neetworkk Desiign，Netwo

6、ork Maanagemment，VoIP，Perfoormancce Evaaluatiion，Analyysis，Simullationn，OPNETT 1 IIntrodductioonThese ddays aa masssive ddeployyment of VooIP iss takiing pllace over data netwoorks. Most of thhese nnetworrks arre Ethhernett basedd and rrunninng IP protoocol. Many netwoork maanagerrs aree findiing it

7、t veryy attrractivve andd costt effeectivee to mmerge and unifyy voicce andd dataa netwworks into one. It iss easiier too run, managge, annd maiintainn. Howwever, one has tto keeep in mind that IP neetworkks aree bestt-effoort neetworkks thaat werre dessignedd for nnon-reeal tiime appplicaationss. O

8、n the oother hand, VoIPP requiires ttimelyy packket deeliverry witth loww lateency, jitteer, packeet losss, annd suffficieent baandwiddth. TTo achhieve this goal, an effficieent deeploymment oof VoIIP musst enssure tthese real-time trafffic reequireementss can be guuarantteed oover nnew orr exisstin

9、g IP neetworkks. When deplooying a neww netwwork sservicce succh as VoIP over existting nnetworrk, maany neetworkk archhitectts, maanagerrs, plannners, desiggners, and enginneers are ffaced with commoon strattegic, and somettimes challlenginng, quuestioons. WWhat aare the QQoS reequireementss for Vo

10、IP? How will the nnew VooIP load impacct thee QoS for ccurrenntly rrunninng nettwork serviices and aappliccationns? Wiill myy exissting netwoork suupportt VoIPP and ssatisffy thee stanndardiized QQoS reequireementss? If so, hhow many VoIP callss can the nnetworrk suppport beforre upggradinng premaat

11、urelly anyy partt of tthe exxistinng nettwork hardwware? Thesee challlengiing quuestioons haave leed to the ddeveloopmentt of soome coommerccial ttools for ttestinng thee perfformannce off multiimediaa appllicatiions iin datta nettworkss. A llist oof thee availlable commeerciall toolls thaat supppor

12、t VoIP is liisted in 1,2. Forr the most part, thesse toools usse twoo commmon approoachess in aassesssing tthe deeploymment oof VoIIP intto thee existting nnetworrk. Onne appproachh is bbased on fiirst pperforrming netwoork meeasureementss and then prediictingg the netwoork readiiness for ssupporrti

13、ng VoIP. The prediictionn of tthe netwoork reeadineess iss baseed on assesssing the hhealthh of netwoork ellementts. Thhe seccond aapproaach iss baseed on injeccting real VoIP trafffic innto exxistinng nettwork and measuuring the rresultting ddelay, jittter, aand looss. Otherr thann the cost assocci

14、atedd withh the commeerciall toolls, none of thhe commmerciial toools ooffer a commpreheensivee approoach ffor suuccesssful VVoIP ddeployyment. In parrticullar, none givess any prediictionn for the ttotal numbeer of callss thatt can bbe suppporteed by the nnetworrk takking iinto aaccounnt imporrtant

15、 desiggn andd engiineeriing faactorss. Theese faactorss incluude VooIP fllow annd calll disstribuution, futuure grrowth capaccity, perfoormancce thrreshollds, iimpactt of VVoIP oon existting nnetworrk serrvicess and appliicatioons, aand immpact backggroundd trafffic oon VoIIP. Thhis paaper aattemppt

16、s too addrress thosee impoortantt facttors aand laayout a commpreheensivee methoodologgy forr a suuccesssful ddeployyment of anny mulltimeddia appliicatioon succh as VoIP and vvideo confeerenciing. Howevver, tthe paaper ffocusees on VoIP as thhe neww servvice oof interrest tto be deplooyed. The ppap

17、er also contaains mmany uusefull enginneerinng andd desiign guuideliines, and ddiscussses mmany practtical issuees perrtainiing too the deplooymentt of VVoIP. Thesee issuees incclude charaacteriisticss of VVoIP ttraffiic andd QoS requiiremennts, VVoIP fflow aand caall diistribbutionn, deffiningg fut

18、urre groowth ccapaciity, aand meeasureement and iimpactt of backggroundd trafffic. As a case studyy, we illusstratee how our approoach aand guuideliines ccan bee appllied tto a ttypicaal nettwork of a smalll enteerprisse. The rrest oof thee papeer is organnized as foollowss. Secction 2 preseents aa

19、typiical nnetworrk toppologyy of aa smalll entterpriise too be ussed ass a caase sttudy ffor deeployiing VooIP. SSectioon 3 outliines ppractiical eeight-step methoodologgy to deplooy succeessfullly VooIP inn dataa netwworks. Eachh stepp is ddescriibed in coonsideerablee detaail. SSectioon 4 ddescrii

20、bes iimporttant ddesignn and eengineeeringg deciisionss to bbe madde bassed onn the analyytic and ssimulaation studiies. SSectioon 5 cconcluudes tthe sttudy aand identtifiess futuure woork.2 Exissting netwoorkFig. 1 illusstratees a ttypicaal nettwork topollogy ffor a smalll enterrprisee resiiding in

21、 a high-rise buildding. The nnetworrk shownn is rrealisstic aand ussed ass a caase sttudy oonly; howevver, our wwork ppresennted iin thiis papper caan be adoptted eaasily for largeer andd geneeral nnetworrks byy folllowingg the same princcipless, guiidelinnes, aand coonceptts laiid outt in tthis ppa

22、per. The nnetworrk is Etherrnet-bbased and hhas twwo Layyer-2 Etherrnet sswitchhes coonnectted byy a roouter. The routeer is Ciscoo 26211, andd the switcches aare 3CCom Suupersttack 33300. Switcch 1 cconneccts Flloors 1 andd 2 annd twoo servvers; whilee Switcch 2 cconneccts Flloor 33 and four servee

23、rs. EEach ffloor LAN is baasicallly a shareed Ethhernett connnectinng empployeee PCs with workggroup and pprinteer serrvers. The netwoork maakes uuse of VLLANs iin ordder too isollate bbroadccast aand muulticaast trrafficc. A tottal off fivee LANss exisst. Alll VLAANs arre porrt bassed. Switcch 1 ii

24、s connfigurred suuch thhat itt has threee VLANNs. VLAN11 inclludes the ddatabaase annd fille serrvers. VLANN2 incluudes FFloor 1. VLLAN3 iincluddes Flloor2. On tthe otther hand, Swittch 2 is coonfiguured tto havve twoo VLANNs. VLLAN4 incluudes tthe seerverss for E-maiil, HTTTP, WWeb annd cacche prox

25、yy, andd fireewall. VLANN5 inccludess Flooor 3. All tthe liinks are sswitchhed Ettherneet 1000 Mbpss fulll dupllex exxcept for tthe linkss for Floorrs 133 whicch aree sharred Ettherneet 1000 Mbpss half dupleex.3 Stepp-by-sstep mmethoddologyyFig. 2 showss a fllowchaart off a meethodoology of eiight s

26、steps for aa succcessfuul VoIIP depploymeent. TThe fiirst ffour ssteps are indeppendennt andd can be peerformmed inn paraallel. Befoore embarrking on thhe anaalysiss and simullationn studdy, inn Stepps 6 and 77, Steep 5 mmust bbe carrried out wwhich requiires aany eaarly and nnecesssary rredimeensio

27、nning oor moddificaationss to tthe existting nnetworrk. Ass showwn, booth Stteps 66 and 7 cann be done in paaralleel. Thhe finnal sttep iss piloot depploymeent.3.1. VooIP trrafficc charracterristiccs, reequireementss, andd assuumptioons For inttroduccing aa new netwoork seervicee suchh as VVoIP, one

28、 has tto chaaracteerize firstt the naturre of its ttraffiic, QooS requiiremennts, aand anny addditionnal coomponeents oor devvices. For ssimpliicity, we aassumee a pooint-tto-poiint coonverssationn for all VVoIP ccalls with no caall coonfereencingg. Forr deplloyingg VoIP, a gaatekeeeper oor Calll Ma

29、nagger noode haas to be addded tto the nnetworrk 3,4,5. The gatekkeeperr nodee handdles ssignalling for eestabllishinng, teerminaating, and authoorizinng connnectiions oof all VVoIP ccalls. Alsoo a VooIP gaatewayy is rrequirred too handdle exterrnal ccalls. A VooIP gaatewayy is rresponnsiblee for co

30、nveertingg VoIP callss to/ffrom tthe Puublic Switcched TTelephhone NNetworrk (PSTNN). Ass an eengineeeringg and desiggn isssue, tthe pllacemeent of thhese nnodes in thhe nettwork becommes crruciall. We will tacklle thiis isssue inn desiign sttep 5. Otheer harrdwaree requiiremennts inncludee a VooIP

31、cllient termiinal, whichh can be a sepparatee VoIPP deviice, ii.e. IIP phoones, or a typiccal PCC or worksstatioon thaat is VoIP-enablled. AA VoIPP-enabbled wworksttationn runs VoIP softwware ssuch aas IP Soft Phonees .Fig. 3 identtifiess the end-tto-endd VoIPP compponentts froom sendeer to receiive

32、r 9. TThe fiirst ccomponnent iis thee encooder whichh periiodicaally ssamplees thee origginal voicee signnal annd assiggns a fixedd numbber off bitss to eeach ssamplee, creeatingg a consttant bbit raate sttream. The tradiitionaal sammple-bbased encodder G.711 uuses PPulse Code Modullationn (PCMM) to

33、 generrate 88-bit samplles evvery 00.125 ms, lleadinng to a datta ratte of 644 kbpss . Thhe paccketizzer foollowss the encodder annd encappsulattes a certaain nuumber of sppeech samplles innto packeets annd addds thee RTP, UDP, IP, and EEthernnet heeaderss. The vvoice packeets trravel throuugh thhe

34、datta nettwork. An imporrtant compoonent at thhe recceivinng endd, is the pplaybaack buffeer whoose puurposee is tto abssorb vvariattions or jiitter in deelay and pprovidde a ssmoothh playyout. Then packeets arre dellivereed to the ddepackketizeer andd evenntuallly to the ddecodeer whiich reconnstru

35、ccts thhe oriiginall voicce signaal. We wiill foollow the wwidelyy adoppted rrecommmendattions of H.3233, G.7711, aand G.714 sstandaards ffor VooIP QooS requiiremennts. Table 11 comppares some commoonly used ITU-TT stanndard codeccs andd the amounnt of one-wway delayy thatt theyy impoose. TTo acccou

36、nt for uupper limitts andd to meet desirrable qualiity reequireement accorrding to ITTU recommmendaation P.8000, we will adoptt G.7111u coodec standdards for tthe reequireed dellay annd banndwidtth. G.711u yieldds aroound 44.4 MOOS ratting. MOS, Mean Opiniion Sccore, is a commoonly uused VVoIP pperf

37、orrmancee metrric giiven iin a scalee of 115, wwith 55 is tthe beest. HHoweveer, wiith liittle comprromisee to qqualitty, itt is ppossibble too impllementt diffferentt ITU-TT codeecs thhat yiield mmuch lless rrequirred baandwiddth peer call and rrelatiively a bitt highher, bbut accceptaable, end-tto

38、-endd delayy. Thiis cann be aaccompplisheed by applyying ccompreessionn, silennce suuppresssion, packket looss coonceallment, queuue managgementt techhniquees, annd enccapsullatingg moree thann one voicee packket innto a singlle Ethhernett framme.3.1.1. End-tto-endd delaay forr a siingle voicee pack

39、ket Fig. 3 illusstratees thee sourrces oof dellay foor a ttypicaal voiice packeet. Thhe endd-to-eend deelay iis sommetimees refferredd to bby M2E oor Mouuth-too-Ear delayy. G.7714 immposess a maaximumm totall one-way ppackett delaay of 150 mms endd-to-eend foor VoIIP appliicatioons . In 222, aa dela

40、ay of up too 200 ms waas consiideredd to bbe accceptabble. WWe cann breaak thiis dellay doown into at leeast tthree diffeerent contrributiing coomponeents, whichh are aas folllows (i) eencodiing, ccompreessionn, andd packketizaation delayy at tthe seender (ii) propaagatioon, trransmiissionn and queu

41、iing deelay iin thee netwwork aand (iiii) bbufferring, decommpresssion, depaccketizzationn, deccodingg, andd playyback delayy at the rreceivver. 3.1.2. Bandwwidth for aa singgle caallThe reqquiredd banddwidthh for a sinngle ccall, one ddirecttion, is 64 kbbps. GG.711 codecc sampples 220 ms of vooice

42、 pper paacket. Thereefore, 50 ssuch ppacketts neeed to be trransmiitted per seconnd. Eaach paacket contaains 1160 vooice ssamplees in orderr to give 8000 samplles peer seccond. Each packeet is sent in onne Etherrnet fframe. Withh everry paccket oof sizze 1600 bytees, headeers off addiitionaal prooto

43、coll layeers arre addded. TThese headeers inncludee RTP+UDP+IP+Etherrnet wwith ppreambble of siizes 112+8+20+26, rrespecctivelly. Thherefoore, aa totaal of 226 bbytes, or 11808 bbits, needss to bbe traansmittted 550 timmes peer seconnd, orr 90.44 kbpss, in one ddirecttion. For bboth ddirecttions, th

44、e rrequirred baandwiddth foor a ssinglee calll is 1100 ppps or 180.88 kbpss assuuming a symmmetriic floow.3.1.3. Otherr assuumptioonsThroughhout oour annalysiis andd workk, we assumme voiice callss are symmeetric and nno voiice coonfereencingg is impleementeed. Wee alsoo ignoore thhe siggnalinng tra

45、affic generrated by thhe gattekeepper. WWe basse ourr anallysis and ddesignn on tthe worstt-casee scennario for VVoIP ccall ttraffiic. Thhe siggnalinng trafffic innvolviing thhe gattekeepper iss mosttly geeneratted prrior tto the eestabllishmeent off the voicee calll and when the ccall iis finisshed

46、. This trafffic iss relaativelly smaall coompareed to the actuaal voiice caall trrafficc. In generral, tthe gaatekeeeper ggeneraates no orr veryy limiited ssignalling ttraffiic thrroughoout thhe durrationn of thhe VoIIP calll forr an aalreaddy esttablisshed oon-goiing caall. In thhis paaper, we wiil

47、l immplemeent noo QoS mechaanismss that can eenhancce thee quallity oof paccket ddeliveery inn IP netwoorks. A myrriad oof QoSS stanndardss are availlable and ccan be ennabledd for netwoork ellementts. QooS staandardds mayy incluude IEEEE 8002.1p/Q, thhe IETTFs RRSVP, and DDiffSeerv. Analyysis oof i

48、mpplemenntatioon cosst, coomplexxity, managgementt, and bbenefiit musst be weighhed caarefullly beefore adoptting ssuch QoS sstandaards. Thesee stanndardss can be reecommeended when the ccost ffor uppgradiing soome neetworkk elemments is hiigh annd the nnetworrk ressourcees aree scarrce annd heaavil

49、y loadeed.3.2. VooIP trrafficc floww and call distrributiionKnowingg the curreent teelephoone caall ussage oor vollume oof the eenterpprise is ann impoortantt stepp for a succcessfful VooIP deplooymentt. Beffore eembarkking oon furrther analyysis oor plannning pphasess for a VoIIP depploymeent, ccol

50、leccting statiisticss aboutt of tthe prresentt calll voluume annd proofiless is eessenttial. Sourcces off suchh infoormatiion arre orgganizaations PBXX, telepphone recorrds annd billls. KKey chharactteristtics oof exiistingg callss can incluude thhe nummber oof callls, nnumberr of cconcurrrent calls

51、s, timme, duuratioon, ettc. Itt is iimporttant tto detterminne thee locattions of thhe calll enddpointts, i.e. thhe souurces and destiinatioons, aas welll as theirr corrresponnding path or fllow. This will aid iin ideentifyying tthe caall diistribbutionn and the ccalls made interrnallyy or eexternna

52、lly. Calll disttributtion mmust iincludde perceentagee of ccalls withiin andd outsside oof a ffloor, buillding, deparrtmentt, or organnizatiion. AAs a ggood ccapaciity pllanninng measuure, iit is recommmendeed to base the VVoIP ccall distrributiion onn the busy hour trafffic off phonne callls foor t

53、hee busieest daay of a weeek or a monnth. TThis wwill eensuree suppport oof the ccalls at alll timmes wiith hiigh QooS forr all VoIP callss. Wheen such curreent sttatisttics aare coombineed witth thee projjectedd extrra callss, we can ppredicct thee worsst-casse VoIIP traaffic load to bee introoduce

54、dd to tthe exxistinng nettwork. Fig. 4 descrribes the ccall distrributiion foor thee enteerprisse undder sttudy bbased on thhe worst busy hour and tthe prrojectted fuuture growtth of VoIP callss. In the ffiguree, thee calll disttributtion iis desscribeed as a proobabillity tree. It iis alsso posssib

55、lee to ddescriibe itt as aa probbabiliity maatrix. Some imporrtant obserrvatioons caan be made aboutt the voicee trafffic fflow ffor innter-ffloor and eexternnal caalls. For aall thesee typee of ccalls, the voicee trafffic hhas too be aalwayss routted throuugh thhe rouuter. This is soo becaause SSwi

56、tchhs 1 aand 2 are layerr 2 swwitchees witth VLAANs coonfiguuratioon. Onne cann obserrve thhat thhe traaffic flow for iinter-floorr callls bettween Floorrs 1 aand 2 imposses twwice tthe looad onn Swittch 1, as tthe trafffic haas to pass throuugh thhe swiitch tto thee routter annd bacck to thhe swiit

57、ch aagain. Simiilarlyy, Swiitch 22 expeeriencces twwice the lload ffor exxternaal callls frrom/too Flooor 3.3.3. Deefine perfoormancce thrreshollds annd groowth ccapaciity In thiss stepp, we definne thee netwwork pperforrmancee thressholdss or ooperattionall poinnts foor a nnumberr of iimporttant ke

58、y nnetworrk eleementss. Theese thhreshoolds aare too be consiideredd whenn deplloyingg the new sservicce. Thhe bennefit is twofoold. FFirst, the requiiremennts off the new sservicce to be deplooyed aare saatisfiied. SSecondd, addding tthe neew serrvice leavees thee netwwork hhealthhy andd suscceptib

59、ble too futuure grrowth. Two iimporttant pperforrmancee critteria are tto be takenn intoo accouunt. FFirst is thhe maxximum tolerrable end-tto-endd delaay; and ssecondd is tthe uttilizaation boundds or thressholdss of nnetworrk resouurces. The maximmum toolerabble ennd-to-end ddelay is deterrminedd

60、by tthe moost seensitiive appplicaation to ruun on the netwoork. IIn ourr casee, it is 1550 ms end-tto-endd for VoIP. It iis imperrativee to nnote tthat iif thee netwwork hhas ceertainn delaay sensiitive appliicatioons, tthe deelay ffor thhese aappliccationns shoulld be monittored, whenn intrroducii