基于RTP協(xié)議的實(shí)時(shí)語(yǔ)音傳輸研究與實(shí)現(xiàn)

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1、摘要近些年來(lái)，因特網(wǎng)的應(yīng)用非常廣泛，除了傳統(tǒng)的http、ftp和電子郵件(Email)外，已經(jīng)出現(xiàn)了越來(lái)越多的多媒體通信業(yè)務(wù)，這些業(yè)務(wù)的一個(gè)共同的特點(diǎn)就是對(duì)實(shí)時(shí)性要求很高。但是，傳統(tǒng)傳輸層協(xié)議設(shè)計(jì)時(shí)的定位決定了它們?cè)趥鬏斘淖?、圖形等離散媒體時(shí)尚能勝任，而不適合語(yǔ)音、視頻等實(shí)時(shí)業(yè)務(wù)的傳輸，為此IESG在1995年通過(guò)了RTP作為因特網(wǎng)建議標(biāo)準(zhǔn)。本文首先介紹了實(shí)時(shí)數(shù)據(jù)傳輸?shù)陌l(fā)展及國(guó)內(nèi)外的研究狀況，研究了分組網(wǎng)絡(luò)上音頻數(shù)據(jù)傳輸?shù)奶攸c(diǎn)。在介紹了實(shí)時(shí)傳輸協(xié)議RTP的特點(diǎn)、構(gòu)成后，詳細(xì)分析了RTP/RTCP協(xié)議，具體闡述了各種報(bào)文的格式及其字段的意義。之后詳細(xì)介

2、紹了Windows下采用雙向鏈表和單緩沖技術(shù)、基于RTP協(xié)議實(shí)時(shí)語(yǔ)音傳輸軟件的實(shí)現(xiàn)，介紹了軟件的基本框架及主要數(shù)據(jù)結(jié)構(gòu)，詳細(xì)介紹了軟件的具體實(shí)現(xiàn)流程，主要包括：音頻數(shù)據(jù)的采集和播放；RTP數(shù)據(jù)包的發(fā)送和接收；補(bǔ)償發(fā)送方和接收方時(shí)鐘速率的偏差和網(wǎng)絡(luò)抖動(dòng)現(xiàn)象，計(jì)算正確的播放時(shí)間。通過(guò)在合適的時(shí)機(jī)調(diào)整去抖緩沖延時(shí)，自動(dòng)適應(yīng)網(wǎng)絡(luò)狀態(tài)的變化，有效去除語(yǔ)音分組的抖動(dòng)問(wèn)題，在時(shí)延與丟包之間達(dá)到良好平衡，改善了語(yǔ)音通話質(zhì)量。為了保證一定的QoS，本文根據(jù)報(bào)文丟失率評(píng)估信道的傳輸質(zhì)量和網(wǎng)絡(luò)的擁塞程度，調(diào)整發(fā)送方輸出的碼流，使之自動(dòng)適應(yīng)網(wǎng)絡(luò)狀態(tài)的變化，降低網(wǎng)絡(luò)擁塞產(chǎn)生的

3、概率。關(guān)鍵詞：實(shí)時(shí)傳輸協(xié)議;語(yǔ)音傳輸;時(shí)延;抖動(dòng)IAbstractInrecentyears,Internethasbeenwidelyused.Besideshttp、ftpandEmailservices,ithasmanynewapplications,suchasmultimediacommunication.Thecommonfeatureofthesenewservicesisthestrongrequirementofreal-timereality.Butthedesignprincipleforclassicaltransportp

4、rotocoldecidesthattheycanbecompetentfordiscretemediatransmission,suchastext、pictureetc,butcan'tbeusedforreal-timeservicessuchasaudio、videoandsoon.Thus,inordertotransmitreal-timemediawithhighperformanceoverIPnetwork,onNovember22,1995,RTPwasapprovedbytheIESGasanInternetproposedst

5、andard.First,thepaperintroducesthedevelopmentofthereal-timedatatransmissionandthecurrentresearchinChinaandabroad,thentakesresearchonthecharacteristicsofvoicetransmissionoverpacketnetworks.Inthesecondpart,afterintroducingthefundamentalfeaturesofRTPanditsstandardelements,thepaper

6、presentstheanalysisofRTP/RTCPindetail,includingtheprotocolpacketsformatsandvariousfieldsmeaning.Afterthatthepaperintroduceshowtoimplementthesystemofreal-timeaudiotransmissionbasedonRTPsuiteinWindowsindetail,includingthebasicframestructureandthemaindatastructuresofthesystem.Them

7、ainpartsofthissystemarepresented,including:howtocollectandplayoutaudiodata;howtosendandreceiveRTPpackets;howtocompensateforrelativeclockskewbetweensenderandreceiver,compensateforvariationininterpackettimingcausedbynetworkqueuingjitterandroutechanges,sotocalculatethecorrectplayo

8、uttime.Thesystemadjuststheplayoutbufferingdelayatprope