四川大学计算机网络通信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

(往返计时和超时)Q:howtosetTCPtimeoutvalue?longerthanRTTnote:RTTwillvarytooshort:prematuretimeoutunnecessaryretransmissionstoolong:slowreactiontosegmentlossQ:howtoestimateRTT?SampleRTT(RTT采样):

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贼T看CP愿F找lo皂w拒Co戴nt溉ro劳lre访ce捐iv牙er抓:ex蚁pl透ic挺it谅ly草i栋nf穴or讨ms画s贤en逮de煮r薄of乡丰(栋dy鸣na篇mi常ca绪ll去y湾ch见an隆gi练ng罚)轰am亮ou把nt刃o呢f阳fr趣ee哑b披uf记fe诞r寺sp莫ac司eRc划vW衫in袖do绞wfi虫el距din潮T伶CP坦s搬eg虫me奴ntse有nd纯er哑:ke丑ep孔s甚th沾e呀am别ou吼nt解o薄f妈tr续an即sm射it删te避d,un汇AC落Ke愧dda缓ta录l截es铸s恩th险an辆m呆os差t违re张ce牺nt胡ly闹r付ec寸ei去ve壤dRc剑vW册in锻do蜓wse训nd熔er护w激on剂’t榜o务ve被rr当unre知ce甩iv母er峡’s因b栏uf陈fe摔rs帮b谢ytr悔an偷sm巴it汽ti演ng减t捆oo不m犬uc但h,to术o麦fa肥stflowcontrolre绝ce睁iv草er馒b齿uf荣fe蚂ri扯ngRc垦vB酷uf召fe怎r=售si究ze夏o警r盛TC卖P伯Re帝ce骂iv诞e莫Bu萍ff铁erRc燥vW垂in队do跌w=葱am请ou最nt缓o益f牢sp敞ar遭e蛋ro却om狂i阿n笼Bu捷ff循er103:堂T串ra仍ns凤po迈rt盖L索ay胸er3.贪5.邻6越TC劝P彻Co给nn性ec冷ti嘴on声M战an住ag淘em数en妇tRe恩ca搜ll某:TC森P烦se愤nd断er蹦,逢re鲁ce鹊iv哀er诉e应st慈ab柏li总sh妨“饮co病nn寻ec尘ti脚on怖”双be劳fo秩re塞e丑xc枝ha者ng确in享g阔da饲ta福s地eg容me肝nt国sin翠it罩ia键li阅ze五T溉CP演v絮ar西ia父bl般es腔:se土q.亚#吴sbu归ff盼er缘瑞s,刚f泥lo录w得co叉nt耳ro载l摘in把fo下(花e.今g.Rc茄vW叼in浪do栏w)cl流ie辰nt听:co栗nn铲ec奶ti档on灵i恰ni蓬ti烫at捐orSo岂ck芽etcl哪ie愈nt樱So掉ck熔et=巡寿ne劝w灵So别ck画et完("排ho自st丘na姓me唯",驻"p津or喇t榜nu惑mb塞er怀")无;se饿rv浸er闷:co智nt柏ac连te步d诵by广c别li区en辆tSo按ck砌etco飞nn繁ec伐ti返on玩So寒ck壶et=we拣lc赌om泰eS确oc裂ke烧t.慰ac顺ce见pt()怖;Th撞re胖e亩wa厨y香ha战nd帽sh炸ak窜e:St棉ep工1填:cl妄ie劈燕nt还e仓nd镜s络ys停te卵m养se坐nd畜s伪TC翠P旦SY代N问co富nt荐ro究l扬se座gm区en漫t习to逆s穗er包ve诸rsp棋ec钟if宝ie细s策in午it庭ia锻lse星q#St诞ep扫2权:se尊rv静er批e苹nd净s督ys漂te纱m奔re踏ce精iv捎es民S犁YN忽,拴re押pl页ie西s插wi庭th枪S档YN道AC啊K脸co坏nt隔ro衔l陈se吐gm限en躲tAC背Ksre谈ce宝iv朝ed僵S钩YNal秒lo挥ca性te强s听bu饭ff腾er葛ssp暴ec轮if臭ie管s土se忠rv拆er舍->闭r抛ec都ei估ve栽r测in基it顿ia炮l炊se纳q.也#St驾ep谦3图:cl烧ie某nt驼e掏nd科s变ys纹te桂m坚se绳nd拌s验AC仓K俭co认nt弊ro岂l搞se符gm宏en萄t懒to崇s疫er递ve咏ral筛lo签ca作te校s触bu张ff闸er丧s113:技T感ra榜ns托po缘瑞rt宰L御ay灿erTh替re单e栽wa重y室ha育nd恼sh谷ak俘e:clientSYN(seq=x)serverSYNACK(seq=y,ack=x+1)ACK(ack=y+1)InitiateaconnectionAcceptandacknowledgeAcceptSYNACKandacknowledge123:竭T熟ra绸ns厚po腾rt指L局ay肾erTC浅P淋Co技nn营ec穴ti钩on诞M终an饼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这ec列ti握on阻:cl圾ie倚nt院c著lo酒se梳s桥so遍ck辟et辩:cl叔ie刘nt益So兄ck种et涉.c掠lo好se()垂;St怕ep虾1晶:cl沾ie岂nten猎d场sy图st估em话s荷en缎ds亿T限CP集F呢IN氧c辟on脾tr谊ol惯s状eg抱me率nt肆t慕o眼se芝rv躲erSt驻ep嚼2编:se聚rv狭erre本ce委iv心es牢F窑IN鸭,沟re陵pl芝ie酿s纽奉wi蓬th演A捆CK渔.盟Cl绢os冷es曲c束on皂ne裂ct絮io难n,商s民en拜ds朵F野IN羞.clientFINserverACKACKFINclosecloseclosedtimedwait133:秤T机ra掏ns拍po多rt悄L质ay检erTC念P夫Co召nn况ec认ti俗on广M脉an结ag须em愧en喷t街(c嫌on鞭t.恶)St此ep蛛3田:cl占ie屈ntre权ce嗽iv颠es丝式F味IN担,哈re封pl壤ie巡寿s妇wi怨th想A欲CK汗.En动te题rs饼“夏ti挂me膏d绑wa批it桶”废-止wi颠ll莲r野es盐po喷nd下w菜it兵h净AC悲K贵to羞r彼ec竿ei但ve荐dFI次NsSt医ep括4茎:se蜻rv狭erre离ce垄iv严es太A滨CK页.交C败on嚼ne做ct户io熟n纲cl写os森ed西.No萍te眯:wi校th突s艇ma鸡ll饼m掠od腥if餐ic茄at梨io室n,咽c倚an玩h宣an欺dl饰e孤si恐mu没lt剪an丑eo变usFI溜Ns.cl醉ie滔ntFI沫Nse挤rv售erAC挽KAC棒KFI坚Ncl颂os奖in骗gcl聪os总in斗gcl黄os筛edti体me虾d匪wa卡itcl限os亏ed143:豆T译ra钓ns首po王rt筝L看ay吨erTC摔P韵Co拐nn喂ec套ti锡on系M债an顶ag铜em欣en晨t水(c李on并t)TC闻P姜cl叔ie族ntli忙fe突cy尤cl苍eTC猪P甩se督rv货erli痒fe翁cy宝cl脉e153:售T浩ra衡ns禽po总rt绪L扬ay连er3.项6转Pr蓝in攻ci阁pl属es议o侦f俊Co押ng技es戒ti删on艺C锣on慢tr迟olCo滚ng闸es宫ti右on剑:in害fo北rm漆al霉ly缘瑞:招“t腐oo战m难an冻y央so枝ur华ce削s伍se伏nd祝in与g图to近o疤mu巨ch生d太at识a株to普o途fa权st虎f昆orne床tw愤or学kto谜h调an醒dl江e”di身ff蹄er掩en吐t小fr拍om林f锄lo腹w辣co希nt齿ro汁l!ma杜ni枣fe跟st悼at非io效ns爬:lo嘉st滋p严ac涂ke薯ts极(掌bu鞋ff柳er痒o勒ve缓rf谷lo仙w沾at站r浮ou鲜te骄rs亩)lo舌ng冒d及el犁ay昂s梨(q王ue请ui杜ng适i剃n呼ro屋ut艰er萍b纯uf染fe告rs希)a枕to字p-醋10雾p怜ro蒙bl逝em躁!163:史T荣ra晃ns随po康rt钢L膊ay仪er3.寸7胸TC慌P艇Co刊ng枪es守ti暂on慕C境on维tr桐olen上d-凑en塘d斥co邻nt装ro印l渗(n晚o杰ne桃tw煤or节k催as蕉si鉴st立an揪ce饮)tr星an证sm伪is遇si冲on注r辰at仓e魔li训mi慎te连d拥by权c土on毙ge策st刮io味n悬wi职nd摇ow易s筛iz材e,Co倚ng端wi软n,显ov闯er溜s买eg峰me偶nt哲s:w铁se槐gm竞en总ts海,狗ea晃ch增w寸it德h尼MS伐S杨by坐te呜s灾se叙nt鸟i驰n逢on续e掌RT功T:throughput=

w*MSS

RTT

Bytes/secCo筐ng喇wi影n173:当T欠ra暑ns亏po枪rt源L响ay宫erTC岔P塞co惰ng准es艇ti内on亏c著on颗tr安ol袍:tw地o延“p曲ha世se颤s”sl粮ow御s呆ta男rtco今ng扇es齐ti隔on殃a至vo叹id唤an乞ceim笨po峰rt俊an发t械va新ri逗ab朽le融s:Co看ng扒wi蒜nth客re犁sh阶ol乒d:de虎fi闪ne惊s佣th捧re李sh包ol双d圣be伟tw引ee谣n预tw逼o羞sl消ow殃s洒ta丈rt委p赠ha御se雁,姨co救ng疫es滴ti坊on围c塘on冤tr仍ol司p拖ha马se“pr抵ob双in摧g”fo户r毙us危ab平le芒b哲an砖dw杀id照th肚:id菜ea金ll颜y:tr旬an躺sm贱it苗a砌s旺fa须st揪a卖s闸po停ss裁ib鼓le医(Co遮ng绵wi研nas劈燕l钻ar召ge霜a脉s返po融ss送ib鞋le巾)罩wi微th疯ou情t什lo判ssin梢cr皇ea贺seCo剂ng讽wi蚀nun坡ti缴l畅lo抓ss狭(血co父ng配es峡ti揭on流)lo钱ss送:de钉cr蝴ea配seCo麦ng遭wi世n,码th蓝en颂b涝eg巧in部p复ro扑bi喉ng呜(洒in灰cr诱ea孩si皇ng也)月ag狗ai疑n183:奸T氧ra护ns声po不rt馋L面ay鼓erTC置PSl霜ow岛st猴ar怖tex继po誉ne缝nt响ia很l悬in窃cr押ea线se肝(吊pe占r忆RT哲T)跟i春n杯wi鱼nd偶ow号s绞iz匀e漂(n钞ot舅s蓄o惯sl型ow劣!)lo敲ss融e白ve柜nt档:障ti朱me遇ou临t量(T绳ah燃oe台T较CP家)匆an姓d/迁or遍o慈r盖th剂re薄e艇du桑pl伏ic惰at秘eAC恢Ks(R你en宫o谣TC月P)in仿it躲ia创li喜ze喇:Co到ng琴wi惠n=蒙1fo嫩r耐(e刷ac想h拌se挡gm万en蚂tAC铲Ke郑d)Co篇ng微wi只n++un精ti司l纱(l期os厚s令ev域en旱t副ORCo塑ng组Wi扑n>敢th舒re躲sh器ol寸d)SlowstartalgorithmHo居st业Aon粘e冤se遣gm逗en勿tRT澡THo之st枕Btimetw崖o挂se部gm疤en绍tsfo叹ur夏s虏eg年me洞nt款s193:侧T防ra鸣ns沙po出rt窑L狗ay投erTC域P雀Co沈ng啄es壤ti垮on袜A底vo催id沫an州ce/*sl汉ow狠st织ar翠tis卖o脚ve设r清*竹//*Co忧ng粘wi苗n>犁th每re虽sh初ol芳d吊*/Un见ti微l药(l怜os失s荐ev造en传t)但{ev周er姜y登w禾se燃gm拒en弓tsAC讯Ke肿d:Co火ng林wi柱n++}th仪re匹sh榆ol火d灿=茅Co建ng饥wi科n/惨2Co丧ng悟wi乐n=赤1pe么rf绝or决msl茫ow伟st用ar愿tCo蒙ng裙es泰ti脖on葬a危vo料id测an丛ce1203:彻T酬ra命ns昏po数rt柜L层ay纤erTC趟P晋Fa桨ir导ne批ssFa两ir吧ne彼ss尸g畜oa思l:if朗N亿T维CP消s躲es豆si庆on哗s卖sh找ar茫e喝sa妻me紧b吸ot炮tl塌en胆ec愤k栽li盏nk燥,笼ea溉ch散s达ho铁ul陡d贵ge晒t刑1/别N奶of亩l森in军k怒ca己pa垄ci已tyTC尼P煎co胳ng至es础ti胁on挽a炸vo结id负an偏ce享:AI雕MD眯:ad甘di温ti托ve陵i要nc己re帆as甜e,熄m扬ul忆ti倡pl踢ic滩at北iv驱e奴de锹cr击ea驳sein咳cr享ea纤se扯w矮in碍do乏w劝by熊1汇p狮er笔R翠TTde我cr涂ea味se裹w也in损do衫w约by资f诸ac蚂to者r隆of惧2责o疮n需lo冤ss受e续ve垃ntAI津MDTC细P肤co岩nn虑ec志ti之on梨1bo款tt洁le己ne坡ckro将ut亦erca恳pa给ci纲ty六RTC疾Pco系nn蜂ec捆ti家on践2213:扮T菠ra怕ns区po袋rt常L星ay吩erWh侧y乓is驶T闹CP并f拆ai绪r?Tw火o共co症mp释et追in庸g蔬se耽ss馅io垄ns托:Ad晓di捷ti域ve往i饮nc袄re保as伯e稿gi降ve瓦s督sl颜op砖e舒of酒1央,漆as美t奴hr铲ou丧