四川大學計算機網(wǎng)絡通信5

3.5Connection-OrientedTransport:TCP

Overview

RFCs:793,1122,1323,2018,2581

3.5.1TheTCPConnectionfullduplexdata:bi-directionaldataflowinsameconnectionMSS:maximumsegmentsizeconnection-oriented:

handshaking(exchangeofcontrolmsgs)init’ssender,receiverstatebeforedataexchangeflowcontrolled:senderwillnotoverwhelmreceiverpoint-to-point:onesender,onereceiver

reliable,in-orderbytestream:no“messageboundaries”pipelined:TCPcongestionandflowcontrolsetwindowsizesend&receivebuffers13:TransportLayer3.5.2TCPsegmentstructuresourceport#destport#32bitsapplicationdata(variablelength)sequencenumberacknowledgementnumberrcvrwindowsizeptrurgentdatachecksumFSRPAUheadlennotusedOptions(variablelength)URG:urgentdata(generallynotused)ACK:ACK#validPSH:pushdatanow(generallynotused)RST,SYN,FIN:Connectionestablishment(setup,teardowncommands)#bytesrcvrwillingtoacceptcountingbybytesofdata(notsegments!)Internetchecksum(asinUDP)23:TransportLayerTCPseq.#’sandACKsSeq.#’s:bytestream“number”offirstbyteinsegment’sdataACKs:seq#ofnextbyteexpectedfromothersidecumulativeACKQ:howreceiverhandlesout-of-ordersegmentsA:TCPspecdoesn’tsay,-uptoimplementorHostAHostBSeq=42,ACK=79,data=‘C’Seq=79,ACK=43,data=‘C’Seq=43,ACK=80Usertypes‘C’hostACKsreceiptofechoed‘C’hostACKsreceiptof‘C’,echoesback‘C’timesimpletelnetscenario33:TransportLayer3.5.3TCPRoundTripTimeandTimeout

(往返計時和超時)Q:howtosetTCPtimeoutvalue?longerthanRTTnote:RTTwillvarytooshort:prematuretimeoutunnecessaryretransmissionstoolong:slowreactiontosegmentlossQ:howtoestimateRTT?SampleRTT(RTT采樣):

measuredtimefromsegmenttransmissionuntilACKreceiptignoreretransmissions,cumulativelyACKedsegmentsSampleRTTwillvary,wantestimatedRTT“smoother”useseveralrecentmeasurements,notjustcurrentSampleRTT43:TransportLayerTCPRoundTripTimeandTimeoutEstimatedRTT=(1-x)*EstimatedRTT+x*SampleRTTExponentialweightedmovingaverageinfluenceofgivensampledecreasesexponentiallyfasttypicalvalueofx:

0.125SettingthetimeoutEstimtedRTTplus“safetymargin”(安全空白）largevariationinEstimatedRTT->largersafetymarginTimeout=EstimatedRTT+4*DeviationDeviation(偏差)=(1-x)*Deviation+x*|SampleRTT-EstimatedRTT|53:TransportLayer3.5.4TCP:reliabledatatransfersimplifiedsender,assumingwaitforeventwaitforeventevent:datareceivedfromapplicationaboveevent:timertimeoutforsegmentwithseq#yevent:ACKreceived,withACK#ycreate,sendsegmentretransmitsegmentACKprocessingonewaydatatransfernoflow,congestioncontrol63:TransportLayerTCP:reliabledatatransfer00

sendbase=initial_sequencenumber01nextseqnum=initial_sequencenumber0203loop(forever){

04switch(event)

05event:datareceivedfromapplicationabove06createTCPsegmentwithsequencenumbernextseqnum07starttimerforsegmentnextseqnum08passsegmenttoIP09nextseqnum=nextseqnum+length(data)10event:timertimeoutforsegmentwithsequencenumbery11retransmitsegmentwithsequencenumbery12computenewtimeoutintervalforsegmenty13restarttimerforsequencenumbery14event:ACKreceived,withACKfieldvalueofy15if(y>sendbase){/*cumulativeACKofalldatauptoy*/16cancelalltimersforsegmentswithsequencenumbers<y17sendbase=y18}19else{/*aduplicateACKforalreadyACKedsegment*/20incrementnumberofduplicateACKsreceivedfory21if(numberofduplicateACKSreceivedfory==3){22/*TCPfastretransmit*/23resendsegmentwithsequencenumbery24restarttimerforsegmenty25}26}/*endofloopforever*/

SimplifiedTCPsender73:TransportLayerTCPACKgeneration

[RFC1122,RFC2581]Eventin-ordersegmentarrival,nogaps,everythingelsealreadyACKedin-ordersegmentarrival,nogaps,onedelayedACKpendingout-of-ordersegmentarrivalhigher-than-expectseq.#gapdetectedarrivalofsegmentthatpartiallyorcompletelyfillsgapTCPReceiveractiondelayedACK.Waitupto500msfornextsegment.Ifnonextsegment,sendACKimmediatelysendsinglecumulativeACKsendduplicateACK,indicatingseq.#ofnextexpectedbyteimmediateACKifsegmentstartsatlowerendofgap83:TransportLayerTCP:retransmissionscenariosHostASeq=92,8bytesdataACK=100losstimeouttimelostACKscenarioHostBXSeq=92,8bytesdataACK=100HostASeq=100,20bytesdataACK=100Seq=92timeouttimeprematuretimeout,cumulativeACKsHostBSeq=92,8bytesdataACK=120Seq=92,8bytesdataSeq=100timeoutACK=12093:TransportLayer3.益5.反5賊T看CP愿F找lo皂w拒Co戴nt溉ro勞lre訪ce捐iv牙er抓:ex蟻pl透ic挺it諒ly草i棟nf穴or討ms畫s賢en逮de煮r薄of鄉(xiāng)豐(棟dy鳴na篇mi常ca緒ll去y灣ch見an隆gi練ng罰)轟am亮ou把nt刃o呢f陽fr趣ee啞b披uf記fe誕r寺sp莫ac司eRc劃vW衫in袖do絞wfi蟲el距din潮T伶CP坦s搬eg蟲me奴ntse有nd純er啞:ke丑ep孔s甚th沾e呀am別ou吼nt解o薄f媽tr續(xù)an即sm射it刪te避d,un匯AC落Ke愧dda緩ta錄l截es鑄s恩th險an輛m呆os差t違re張ce犧nt胡ly鬧r付ec寸ei去ve壤dRc劍vW冊in鍛do蜓wse訓nd熔er護w激on劑’t榜o務ve被rr當unre知ce甩iv母er峽’s因b欄uf陳fe摔rs幫b謝ytr悔an偷sm巴it汽ti演ng減t捆oo不m犬uc但h,to術o麥fa肥stflowcontrolre絕ce睜iv草er饅b齒uf榮fe螞ri扯ngRc墾vB酷uf召fe怎r=售si究ze夏o警r盛TC賣P伯Re帝ce罵iv誕e莫Bu萍ff鐵erRc燥vW垂in隊do跌w=蔥am請ou最nt緩o益f牢sp敞ar遭e蛋ro卻om狂i阿n籠Bu捷ff循er103:堂T串ra仍ns鳳po邁rt蓋L索ay胸er3.貪5.鄰6越TC勸P徹Co給nn性ec冷ti嘴on聲M戰(zhàn)an住ag淘em數(shù)en婦tRe恩ca搜ll某:TC森P煩se憤nd斷er蹦,逢re魯ce鵲iv哀er訴e應st慈ab柏li總sh妨“飲co病nn尋ec塵ti腳on怖”雙be勞fo秩re塞e丑xc枝ha者ng確in享g闊da飼ta福s地eg容me肝nt國sin翠it罩ia鍵li閱ze五T溉CP演v絮ar西ia父bl般es腔:se土q.亞#吳sbu歸ff盼er緣瑞s,剛f泥l(xiāng)o錄w得co叉nt耳ro載l摘in把fo下(花e.今g.Rc茄vW叼in浪do欄w)cl流ie辰nt聽:co栗nn鏟ec奶ti檔on靈i恰ni蓬ti燙at捐orSo豈ck芽etcl哪ie愈nt櫻So掉ck熔et=巡壽ne勸w靈So別ck畫et完("排ho自st丘na姓me唯",駐"p津or喇t榜nu惑mb塞er懷")無;se餓rv浸er悶:co智nt柏ac連te步d誦by廣c別li區(qū)en輛tSo按ck砌etco飛nn繁ec伐ti返on玩So寒ck壺et=we揀lc賭om泰eS確oc裂ke燒t.慰ac順ce見pt()怖;Th撞re胖e畝wa廚y香ha戰(zhàn)nd帽sh炸ak竄e:St棉ep工1填:cl妄ie劈燕nt還e倉nd鏡s絡ys停te卵m養(yǎng)se坐nd畜s偽TC翠P旦SY代N問co富nt薦ro究l揚se座gm區(qū)en漫t習to逆s穗er包ve諸rsp棋ec鐘if寶ie細s策in午it庭ia鍛lse星q#St誕ep掃2權:se尊rv靜er批e蘋nd凈s督y(tǒng)s漂te紗m奔re踏ce精iv捎es民S犁YN忽,拴re押pl頁ie西s插wi庭th槍S檔YN道AC啊K臉co壞nt隔ro銜l陳se吐gm限en躲tAC背Ksre談ce寶iv朝ed僵S鉤YNal秒lo揮ca性te強s聽bu飯ff騰er葛ssp暴ec輪if臭ie管s土se忠rv拆er舍->閉r拋ec都ei估ve栽r測in基it頓ia炮l炊se納q.也#St駕ep謙3圖:cl燒ie某nt駝e掏nd科s變ys紋te桂m堅se繩nd拌s驗AC倉K儉co認nt弊ro豈l搞se符gm宏en萄t懶to崇s疫er遞ve詠ral篩lo簽ca作te校s觸bu張ff閘er喪s113:技T感ra榜ns托po緣瑞rt宰L御ay燦erTh替re單e栽wa重y室ha育nd惱sh谷ak俘e:clientSYN(seq=x)serverSYNACK(seq=y,ack=x+1)ACK(ack=y+1)InitiateaconnectionAcceptandacknowledgeAcceptSYNACKandacknowledge123:竭T熟ra綢ns厚po騰rt指L局ay腎erTC淺P淋Co技nn營ec穴ti鉤on誕M終an餅ag沙em丑en茄t禁(c推on奇t.批)Cl磨os田in刊g怕a召co找nn這ec列ti握on阻:cl圾ie倚nt院c著lo酒se梳s橋so遍ck辟et辯:cl叔ie劉nt益So兄ck種et涉.c掠lo好se()垂;St怕ep蝦1晶:cl沾ie豈nten獵d場sy圖st估em話s荷en緞ds億T限CP集F呢IN氧c辟on脾tr誼ol慣s狀eg抱me率nt肆t慕o眼se芝rv躲erSt駐ep嚼2編:se聚rv狹erre本ce委iv心es牢F窯IN鴨,溝re陵pl芝ie釀s紐奉wi蓬th演A捆CK漁.盟Cl絹os冷es曲c束on皂ne裂ct絮io難n,商s民en拜ds朵F野IN羞.clientFINserverACKACKFINclosecloseclosedtimedwait133:秤T機ra掏ns拍po多rt悄L質(zhì)ay檢erTC念P夫Co召nn況ec認ti俗on廣M脈an結ag須em愧en噴t街(c嫌on鞭t.惡)St此ep蛛3田:cl占ie屈ntre權ce嗽iv顛es絲式F味IN擔,哈re封pl壤ie巡壽s婦wi怨th想A欲CK汗.En動te題rs餅“夏ti掛me膏d綁wa批it桶”廢-止wi顛ll蓮r野es鹽po噴nd下w菜it兵h凈AC悲K貴to羞r彼ec竿ei但ve薦dFI次NsSt醫(yī)ep括4莖:se蜻rv狹erre離ce壟iv嚴es太A濱CK頁.交C敗on嚼ne做ct戶io熟n綱cl寫os森ed西.No萍te瞇:wi校th突s艇ma雞ll餅m掠od腥if餐ic茄at梨io室n,咽c倚an玩h宣an欺dl飾e孤si恐mu沒lt剪an丑eo變usFI溜Ns.cl醉ie滔ntFI沫Nse擠rv售erAC挽KAC棒KFI堅Ncl頌os獎in騙gcl聰os總in斗gcl黃os篩edti體me蝦d匪wa卡itcl限os虧ed143:豆T譯ra釣ns首po王rt箏L看ay噸erTC摔P韻Co拐nn喂ec套ti錫on系M債an頂ag銅em欣en晨t水(c李on并t)TC聞P姜cl叔ie族ntli忙fe突cy尤cl蒼eTC豬P甩se督rv貨erli癢fe翁cy寶cl脈e153:售T浩ra衡ns禽po總rt緒L揚ay連er3.項6轉(zhuǎn)Pr藍in攻ci閣pl屬es議o偵f俊Co押ng技es戒ti刪on藝C鑼on慢tr遲olCo滾ng閘es宮ti右on劍:in害fo北rm漆al霉ly緣瑞:招“t腐oo戰(zhàn)m難an凍y央so枝ur華ce削s伍se伏nd祝in與g圖to近o疤mu巨ch生d太at識a株to普o途fa權st虎f昆orne床tw憤or學kto謎h調(diào)an醒dl江e”di身ff蹄er掩en吐t小fr拍om林f鋤lo腹w辣co希nt齒ro汁l!ma杜ni棗fe跟st悼at非io效ns爬:lo嘉st滋p嚴ac涂ke薯ts極(掌bu鞋ff柳er癢o勒ve緩rf谷lo仙w沾at站r浮ou鮮te驕rs畝)lo舌ng冒d及el犁ay昂s梨(q王ue請ui杜ng適i剃n呼ro屋ut艱er萍b純uf染fe告rs希)a枕to字p-醋10霧p憐ro蒙bl逝em躁!163:史T榮ra晃ns隨po康rt鋼L膊ay儀er3.寸7胸TC慌P艇Co刊ng槍es守ti暫on慕C境on維tr桐olen上d-湊en塘d斥co鄰nt裝ro印l滲(n晚o杰ne桃tw煤or節(jié)k催as蕉si鑒st立an揪ce飲)tr星an證sm偽is遇si沖on注r辰at倉e魔li訓mi慎te連d擁by權c土on斃ge策st刮io味n懸wi職nd搖ow易s篩iz材e,Co倚ng端wi軟n,顯ov闖er溜s買eg峰me偶nt哲s:w鐵se槐gm競en總ts海,狗ea晃ch增w寸it德h尼MS伐S楊by坐te嗚s災se敘nt鳥i馳n逢on續(xù)e掌RT功T:throughput=

w*MSS

RTT

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