英文文献-科技类-原文及翻译-1

1、PAGE PAGE 8外文文献原原文On thhe deeployymentt of VoIPP in Etheernett nettworkks: methhodollogy and casee stuudyAbstrractDeplooyingg IP teleephonny orr voiice oover IP (VoIPP) iss a mmajorr andd chaallenngingg tassk foor daata nnetwoork rreseaarcheers aand ddesiggnerss. Thhis ppaperr outtlinees guuidelline

2、ss andd a sstep-by-sstep methhodollogy on hhow VVoIP can be ddeplooyed succcessffullyy. Thhe meethoddologgy caan bee useed too asssess the suppport and readdinesss off an exisstingg nettworkk. Prrior to tthe ppurchhase and deplloymeent oof VooIP eequippmentt, thhe meethoddologgy prrediccts tthe nnum

3、beer off VoIIP caalls thatt cann be susttaineed byy an exisstingg nettworkk whiile ssatissfyinng QooS reequirremennts oof alll neetworrk seervicces aand lleaviing aadequuate capaacityy forr futture growwth. As aa casse sttudy, we applly thhe meethoddologgy stteps on aa typpicall nettworkk of a smmal

4、l enteerpriise. We uutiliize bboth anallysiss andd simmulattion to iinvesstigaate tthrouughpuut annd deelay bounnds. Our anallysiss is baseed onn queeuingg theeory, andd OPNNET iis ussed ffor ssimullatioon. RResullts oobtaiined fromm anaalysiis annd siimulaationn aree in linee andd givve a closse ma

5、atch. In addiitionn, thhe paaper disccussees maany ddesiggn annd enngineeerinng isssuess. Thhese issuues iincluude ccharaacterristiics oof VooIP ttrafffic aand QQoS rrequiiremeents, VoIIP fllow aand ccall disttribuutionn, deefiniing ffuturre grrowthh cappacitty, aand mmeasuuremeent aand iimpacct off

6、 bacckgroound trafffic. Keywoords: Nettworkk Dessign，Netwwork Manaagemeent，VoIPP，Perfformaance Evalluatiion，Anallysiss，Simuulatiion，OPNEET 1 InttroduuctioonThesee dayys a masssive deplloymeent oof VooIP iis taakingg plaace overr datta neetworrks. Mostt of thesse neetworrks aare EEtherrnet baseed and

7、 runnning IP pprotoocol. Manny neetworrk maanageers aare findding it vvery attrractiive aand ccost effeectivve too merrge aand uniffy vooice and dataa nettworkks innto oone. It iis eaasierr to run, manaage, and mainntainn. Hooweveer, oone hhas tto keeep iin miind thatt IP netwworkss aree besst-efffo

8、rtt nettworkks thhat wwere desiignedd for non-reall timme apppliccatioons. On tthe ootherr hannd, VVoIP requuiress timmely packket ddelivvery withh loww lattencyy, jiitterr, packket lloss, andd suffficiient banddwidtth. TTo acchievve thhis ggoal, an eefficcientt depploymment of VVoIP mustt enssure t

9、hesse reeal-ttime trafffic requuiremmentss cann be guarranteeed oover new or eexistting IP nnetwoorks. Whenn depployiing aa neww nettworkk serrvicee succh ass VoIIP overr exiistinng neetworrk, mmany netwwork archhiteccts, manaagerss, plannnerss, deesignners, andd enggineeers aare ffacedd witth coomm

10、onn straategiic, aand ssomettimess chaallenngingg, quuestiions. Whaat arre the QoS requuiremmentss forr VoIIP? HHow wwill the new VoIPP loadd imppact the QoS for currrentlly ruunninng neetworrk seervicces and appllicattionss? Wiill mmy exxistiing nnetwoork ssuppoort VVoIP and satiisfy the stanndardd

11、izedd QoSS reqquireementts? IIf soo, hoow manyy VoIIP caalls can the netwwork suppport befoore uupgraadingg premmaturrely any partt of the exisstingg nettworkk harrdwarre? Thesse chhalleenginng quuestiions havee ledd to the deveelopmment of ssome commmerciial ttoolss forr tesstingg thee perrformmanc

12、ee of multtimeddia aappliicatiions in ddata netwworkss. A listt of the avaiilablle coommerrciall toools tthat suppport VoIPP is listted iin 1,22. FFor tthe mmost partt, thhese toolls usse twwo coommonn apprroachhes iin asssesssing the deplloymeent oof VooIP iinto the exisstingg nettworkk. Onne apppr

13、oaach iis baased on ffirstt perrformming netwwork meassuremmentss andd theen prredicctingg thee nettworkk readdinesss foor suupporrtingg VoIIP. TThe pprediictioon off thee netwwork readdinesss iss bassed oon asssesssing the heallth oof netwwork elemmentss. Thhe seecondd appproacch iss bassed oon inj

14、eectinng reeal VVoIP trafffic intoo exiistinng neetworrk annd meassurinng thhe reesultting delaay, jjitteer, aand lloss. Otheer thhan tthe ccost assoociatted wwith the commmerciial ttoolss, nonee of the commmerciial ttoolss offfer aa commprehhensiive apprroachh forr succcesssful VoIPP depploymment.

15、In paarticcularr, nonee givves aany pprediictioon foor thhe tootal numbber oof caalls thatt can be ssuppoortedd by the netwwork takiing iinto accoount impoortannt deesignn andd enggineeeringg facctorss. Thhese facttors incllude VoIPP floow annd caall ddistrributtion, futture growwth capaacityy, peer

16、forrmancce thhreshholdss, immpactt of VoIPP on exisstingg nettworkk serrvicees annd apppliccatioons, and impaact backkgrouund ttrafffic oon VooIP. Thiss papper aattemmpts to aaddreess thosse immporttant facttors and layoout aa commprehhensiive methhodollogy for a suuccesssfull depploymment of aany m

17、multiimediia appllicattion suchh as VoIPP andd viddeo confferenncingg. Howeever, thee papper ffocusses oon VooIP aas thhe neew seervicce off inteerestt to be ddeplooyed. Thee papper aalso conttainss manny ussefull engiineerring and desiign gguideelinees, aand ddiscuussess manny praccticaal isssuess

18、perrtainning to tthe ddeplooymennt off VoIIP. TThesee issuues iincluude ccharaacterristiics oof VooIP ttrafffic aand QQoS requuiremmentss, VooIP fflow and calll disstribbutioon, ddefinning futuure ggrowtth caapaciity, and meassuremment and impaact oof backkgrouund ttrafffic. As aa casse sttudy, we i

19、lluustraate hhow oour apprroachh andd guiideliines can be aappliied tto a typiical netwwork of aa smaall eenterrprisse. The restt of the papeer iss orgganizzed aas foollowws. SSectiion 22 pressentss a ttypiccal nnetwoork ttopollogy of aa smaall eenterrprisse too be uused as aa casse sttudy for depll

20、oyinng VooIP. Secttion 3 outlliness praacticcal eeightt-steep meethoddologgy too depploy succcessffullyy VoIIP inn datta neetworrks. Eachh steep iss desscribbed in cconsiideraable detaail. Secttion 4 deescriibes impoortannt deesignn and engiineerring deciisionns too be madee bassed oon thhe annalytt

21、ic and simuulatiion sstudiies. Secttion 5 cooncluudes the studdy annd idenntifiies ffuturre woork.2 Exxistiing nnetwoorkFig. 1 illlusttratees a typiical netwwork topoologyy forr a ssmalll enteerpriise rresidding in aa higgh-riise bbuildding. Thee nettworkk showwn iss reaalisttic aand uused as aa cas

22、se sttudy onlyy; hooweveer, our workk preesentted iin thhis ppaperr cann be adoppted easiily ffor largger aand ggenerral nnetwoorks by ffolloowingg thee samme prinnciplles, guiddelinnes, and concceptss laiid ouut inn thiis paaper. The netwwork is EEtherrnet-baseed annd haas twwo Laayer-2 Etheernett

23、swiitchees coonneccted by aa rouuter. Thee rouuter is Ciscco 26621, and the swittchess aree 3Coom Suupersstackk 33000. Swittch 11 connnectts Flloorss 1 aand 22 andd twoo serrverss; whhile Swittch 22 connnectts Flloor 3 annd foour sserveers. Eachh flooor LLAN is bbasiccallyy a sshareed Etthernnet cco

24、nneectinng emmployyee PPCs withh worrkgrooup aand pprintter sserveers. The netwwork makees usse of VVLANss in ordeer too isoolatee brooadcaast aand mmultiicastt traafficc. A tootal of ffive LANss exiist. All VLANNs arre poort bbasedd. Swittch 11 is conffigurred ssuch thatt it has threee VLLANs. VLAN

25、N1 inncluddes tthe ddatabbase and filee serrverss. VLLAN2 inclludess Flooor 11. VLLAN3 inclludess Flooor2. On the otheer handd, Swwitchh 2 iis coonfigguredd to havee twoo VLAANs. VLANN4 inclludess thee serrverss forr E-mmail, HTTTP, WWeb aand ccachee proxxy, aand ffirewwall. VLAAN5 iincluudes Flooor

26、 3. Alll thee linnks are swittchedd Ethherneet 1000 Mbbps ffull dupllex eexceppt foor thhe linkks foor Flloorss 133 whiich aare sshareed Etthernnet 1100 MMbps halff dupplex.3 Sttep-bby-sttep mmethoodoloogyFig. 2 shhows a fllowchhart of aa metthodoologyy of eighht stteps for a suuccesssfull VoIIP dee

27、ployymentt. Thhe fiirst fourr steeps aare indeependdent and can be pperfoormedd in paraallell. Beeforee embaarkinng onn thee anaalysiis annd siimulaationn stuudy, in SStepss 6 and 7, SStep 5 muust bbe caarrieed ouut whhich requuiress anyy earrly and neceessarry reedimeensiooningg or modiificaationns

28、 too thee exisstingg nettworkk. Ass shoown, bothh Steeps 66 andd 7 ccan bbe donee in paraallell. Thhe fiinal stepp is piloot deeployymentt.3.1. VoIPP traafficc chaaractterissticss, reequirremennts, and assuumptiions For iintrooduciing aa neww nettworkk serrvicee succh ass VoIIP, oone has to ccharaac

29、terrize firsst thhe naaturee of its trafffic, QoSS requuiremmentss, annd anny addditiionall commponeents or ddevicces. For simppliciity, we aassumme a poinnt-too-poiint cconveersattion for all VoIPP callls wwith no ccall confferenncingg. Foor deeployying VoIPP, a gateekeepper oor Caall Manaager node

30、e hass to be aaddedd to the netwwork 3,44,5. Thee gattekeeeper nodee hanndless siggnaliing for estaablisshingg, teerminnatinng, aand aauthooriziing cconneectioons oof all VoIPP callls. Alsoo a VVoIP gateeway is rrequiired to hhandlle exteernall callls. A VooIP ggatewway iis reesponnsiblle foor coonv

31、errtingg VoIPP callls tto/frrom tthe PPubliic Swwitchhed TTelepphonee Nettworkk (PSTTN). As aan enngineeerinng annd deesignn isssue, the placcemennt of tthesee noddes iin thhe neetworrk beecomees crruciaal. WWe wiill tackkle tthis issuue inn dessign stepp 5. Otheer haardwaare requuiremmentss incclud

32、ee a VVoIP clieent ttermiinal, whiich ccan bbe a seeparaate VVoIP deviice, i.e. IP phonnes, or aa typpicall PC or workkstattion thatt is VoIPP-enaabledd. A VoIPP-enaabledd worrkstaationn runss VoIIP sooftwaare ssuch as IIP Sooft Phonnes .Fig. 3 iddentiifiess thee endd-to-end VoIPP commponeents fromm

33、 sendder tto reeceivver 9. The firsst coomponnent is tthe eencodder whicch peerioddicallly ssamplles tthe oorigiinal voicce siignall andd assiigns a fiixed numbber oof biits tto eaach ssamplle, ccreatting a consstantt bitt ratte sttreamm. Thhe trradittionaal saamplee-bassed encooder G.7111 usses PPu

34、lsee Codde Moodulaationn (PCCM) tto geneeratee 8-bbit ssamplles eeveryy 0.1125 mms, lleadiing tto a dataa ratte of 664 kbbps . Thee paccketiizer folllows the encooder and encaapsullatess a ccertaain nnumbeer off speeech sampples intoo packkets and addss thee RTPP, UDDP, IIP, aand EEtherrnet headders

35、. The voicce paacketts trravell thrroughh thee datta neetworrk. AAn impoortannt coomponnent at tthe rreceiivingg endd, iss thee plaaybacck bufffer wwhosee purrposee is to aabsorrb vaariattionss or jittter iin deelay and provvide a smmoothh plaayoutt. Thhen ppackeets aare ddelivveredd to the depaacke

36、ttizerr andd eveentuaally to tthe ddecodder wwhichh recoonstrructss thee oriiginaal vooice signnal. We wwill folllow tthe wwidelly addopteed reecommmendaationns off H.3223, GG.7111, annd G.714 stanndardds foor VooIP QQoS requuiremmentss. Tablee 1 ccompaares somee commmonlly usedd ITUU-T sstanddard c

37、odeecs aand tthe aamounnt off onee-wayy delaay thhat tthey impoose. To aaccouunt ffor uupperr limmits and to meett dessirabble qqualiity rrequiiremeent aaccorrdingg to ITU recoommenndatiion PP.8000, wee willl addopt G.7111u ccodecc stanndardds foor thhe reequirred ddelayy andd banndwiddth. G.7111u y

38、iellds aarounnd 4.4 MOOS raatingg. MOOS, MMean Opinnion Scorre, is aa commmonlly ussed VVoIP perfformaance metrric ggivenn in a scalle off 155, wiith 55 is the bestt. Hooweveer, wwith litttle comppromiise tto quualitty, iit iss posssiblle too impplemeent ddiffeerentt ITU-T coodecss thaat yiield much

39、h lesss reequirred bbandwwidthh perr calll andd rellativvely a biit hiigherr, buut acccepttablee, ennd-too-endd delaay. TThis can be aaccommplisshed by aapplyying comppresssion, sileence supppresssion, paccket losss connceallmentt, quueue manaagemeent ttechnniquees, aand eencappsulaatingg morre thha

40、n oone voicce paackett intto a singgle EEtherrnet framme.3.1.11. Ennd-too-endd dellay ffor aa sinngle voicce paackett Fig. 3 illlusttratees thhe soourcees off dellay ffor aa typpicall voiice packket. The end-to-eend ddelayy is someetimees reeferrred tto byy M2E or MMouthh-to-Ear delaay. GG.7144 impp

41、osess a mmaximmum totaal onne-waay paackett dellay oof 1550 mss endd-to-end for VoIPP appllicattionss . IIn 222, a deelay of uup too 2000 ms was conssiderred tto bee accceptaable. We can breaak thhis ddelayy dowwn intoo at leasst thhree diffferennt coontriibutiing ccompoonentts, wwhichh are as ffoll

42、oows (i) eencodding, commpresssionn, annd paackettizattion delaay att thee sennder (ii) proopagaationn, trransmmissiion aand queuuing delaay inn thee nettworkk andd (iiii) bbuffeeringg, deecomppresssion, depaackettizattion, deccodinng, aand pplaybback delaay att the receeiverr. 3.1.22. Baandwiidth f

43、or a siinglee calllThe rrequiired banddwidtth foor a singgle ccall, onee dirrectiion, is 64 kkbps. G.7711 ccodecc sammpless 20 ms oof vooice per packket. Therreforre, 550 suuch ppackeets nneed to bbe trransmmitteed peer secoond. Eachh paccket conttainss 1600 voiice ssamplles iin orrder to givee 8000

44、0 saamplees peer seecondd. Eaach ppackeet iss sennt inn onee Etheernett fraame. Withh eveery ppackeet off sizze 1660 byytes, headders of aaddittionaal prrotoccol llayerrs arre addded. Theese headders incllude RTP+UDP+IP+Etheernett witth prreambble of ssizess 12+8+20+26, resppectiivelyy. Thhereffore,

45、 a ttotall of 226 bytees, oor 18808 bbits, neeeds tto bee traansmiittedd 50 timees peer secoond, or 990.4 kbpss, inn onee dirrectiion. For bothh dirrectiions, the requuiredd banndwiddth ffor aa sinngle calll is 100 pps or 180.8 kbbps aassumming a syymmettric floww.3.1.33. Otther assuumptiionsThrouug

46、houut ouur annalyssis aand wwork, we assuume vvoicee callls arre syymmettric and no vvoicee connfereencinng iss impllemennted. We alsoo ignnore the signnalinng trraffiic geeneraated by tthe ggatekkeepeer. WWe baase oour aanalyysis and desiign oon thhe worsst-caase sscenaario for VoIPP calll trraffii

47、c. TThe ssignaalingg trafffic invoolvinng thhe gaatekeeeperr is mosttly ggenerratedd priior tto the estaablisshmennt off thee voiice ccall and whenn thee calll iss finiishedd. Thhis ttrafffic iis reelatiivelyy smaall ccompaared to tthe actuual vvoicee calll trraffiic. IIn geeneraal, tthe ggatekkeepe

48、er geeneraates no oor veery llimitted ssignaalingg traafficc thrroughhout the duraationn of tthe VVoIP calll forr an alreeady estaablisshed on-ggoingg calll. In tthis papeer, wwe wiill iimpleementt no QoS mechhanissms thatt cann enhhancee thee quaalityy of packket ddelivvery in IIP netwworkss. A myr

49、iiad oof QooS sttandaards are avaiilablle annd caan be eenablled ffor nnetwoork eelemeents. QoSS staandarrds mmay incllude IEEEE 8022.1p/Q, tthe IIETFs RSSVP, and DifffServv. Anallysiss of impllemenntatiion ccost, commplexxity, mannagemment, and beneefit mustt be weigghed careefullly beeforee adoopt

50、inng suuch QoS stanndardds. TThesee staandarrds ccan bbe reecommmendeed whhen the costt forr upggradiing ssome netwwork elemmentss is highh andd the netwwork resoourcees arre sccarcee andd heaavilyy loaaded.3.2. VoIPP traafficc floow annd caall ddistrributtionKnowiing tthe ccurreent ttelepphonee cal

51、ll ussage or vvolumme off the enteerpriise iis ann impportaant sstep for a suuccesssfull VoIIP deplloymeent. Befoore eembarrkingg on furtther anallysiss or plannningg phaases for a VooIP ddeplooymennt, ccolleectinng sttatissticss abouut off thee preesentt calll voolumee andd proofilees iss esssentii

52、al. Sourrces of ssuch infoormattion are orgaanizaationns PPBX, teleephonne reecordds annd biills. Keyy chaaractterissticss of exisstingg callls caan inncludde thhe nuumberr of callls, nnumbeer off conncurrrent callls, ttime, durratioon, eetc. It iis immporttant to ddeterrminee thee locaationns off t

53、hee calll enndpoiints, i.ee. thhe soourcees annd desttinattionss, ass welll ass theeir ccorreesponndingg patth orr floow. Thiss willl aiid inn ideentiffyingg thee calll diistriibutiion aand tthe ccallss madee intternaally or eexterrnallly. CCall disttribuutionn musst inncludde perccentaage oof caall

54、s withhin aand ooutsiide oof a flooor, bbuildding, depaartmeent, or oorgannizattion. As a goood ccapaccity plannningg meassure, it is rrecommmendded tto baase tthe VVoIP calll disttribuutionn on the busyy houur trraffiic off phoone ccallss forr thee busiiest day of aa weeek orr a mmonthh. Thhis wwil

55、l ensuure ssuppoort oof the callls att alll timmes wwith highh QoSS forr alll VoIIP caalls. Wheen suchh currrentt staatisttics are combbinedd witth thhe prrojeccted extrra callls, wwe caan prredicct thhe woorst-casee VoIIP trraffiic looad tto bee intrroducced tto thhe exxistiing nnetwoork. Fig. 4 de

56、escriibes the calll disttribuutionn forr thee entterprrise undeer sttudy baseed onn thee worst busyy houur annd thhe prrojeccted futuure ggrowtth off VoIIP caalls. In the figuure, the calll disstribbutioon iss desscribbed aas a probbabillity treee. Itt is alsoo posssiblle too desscribbe itt as a prr

57、obabbilitty maatrixx. Somee impportaant oobserrvatiions can be mmade abouut thhe voicce trraffiic fllow ffor iinterr-flooor aand eexterrnal callls. FFor aall thesse tyype oof caalls, thee voiice ttrafffic hhas tto bee alwways routted throough the routter. Thiss is so bbecauuse SSwitcchs 11 andd 2 aa

58、re layeer 2 swittchess witth VLLANs conffigurratioon. OOne ccan obseerve thatt thee traafficc floow foor innter-flooor caalls betwween Flooors 11 andd 2 iimposses ttwicee thee loaad onn Swiitch 1, aas thhe trafffic has to ppass throough the swittch tto thhe roouterr andd bacck to tthe sswitcch aggai

59、n. Simmilarrly, Swittch 22 expperieencess twiice the loadd forr extternaal caalls fromm/to Flooor 3.3.3. Defiine pperfoormannce tthressholdds annd grrowthh cappacitty In thhis sstep, we defiine tthe nnetwoork pperfoormannce threeshollds oor opperattionaal poointss forr a nnumbeer off impportaant key

60、 netwwork elemmentss. Thhese threeshollds aare tto bee conssiderred wwhen deplloyinng thhe neew seervicce. TThe bbeneffit iis twoffold. Firrst, the requuiremmentss of the new servvice to bbe deplloyedd aree sattisfiied. Secoond, addiing tthe nnew sserviice leavves tthe nnetwoork hhealtthy aand ssusc