1、5、 傳輸層協(xié)議分析傳輸層協(xié)議分析 5.1 UDP和和TCP 5.2 傳感網(wǎng)絡(luò)的傳輸層協(xié)議傳感網(wǎng)絡(luò)的傳輸層協(xié)議 現(xiàn)代通信技術(shù)課程現(xiàn)代通信技術(shù)課程主講：宋梁，主講：宋梁，LSONGIEEE.ORGLSONGIEEE.ORGQQQQ群：群：3149458743149458742014-20152014-20152內(nèi)容安排內(nèi)容安排 可靠性要求 傳遞single of packets 傳遞 blocks of packets 傳遞 streams of packets可靠性方面Focus of this tutorialCoverage & deploymentCoverage & d

2、eployment 當(dāng)有事件發(fā)生時(shí)是否有足夠的節(jié)點(diǎn)可以監(jiān)測(cè)事件的發(fā)生？是否有足夠的節(jié)點(diǎn)可以精確地測(cè)量數(shù)據(jù)? 如何布置這些節(jié)點(diǎn)？Information accuracyInformation accuracy 哪些被測(cè)量的數(shù)據(jù)必須被傳送到哪里以保證一定的精確性? 如何在第一時(shí)間內(nèi)處理那些不精確的測(cè)量? Dependable data transport Dependable data transport 一旦確定哪些數(shù)據(jù)被傳送到哪里，如何保證它們準(zhǔn)確地到達(dá)? How to deal with transmission errors transmission errors and omission

3、 omission errors/congestionerrors/congestion?可靠性協(xié)議物理層 物理層是實(shí)現(xiàn)無(wú)線網(wǎng)絡(luò)通信的基石，其可靠性能的優(yōu)劣直接影響到整個(gè)系統(tǒng)的容錯(cuò)能力。物理層主要負(fù)責(zé)數(shù)據(jù)的編碼調(diào)制、解調(diào)解碼、發(fā)送與接收。 對(duì)于無(wú)線傳感器網(wǎng)絡(luò)節(jié)點(diǎn)間的通信，為了使得數(shù)據(jù)能夠被可靠地傳輸或接收，必須要做到高的接收機(jī)靈敏度、低的背景噪聲及較強(qiáng)的抗干擾能力。 可靠性協(xié)議鏈路層 數(shù)據(jù)鏈路層主要負(fù)責(zé)數(shù)據(jù)流的多路選擇、數(shù)據(jù)幀偵測(cè)、媒介訪問(wèn)、差錯(cuò)控制 ，保證了點(diǎn)到點(diǎn)、點(diǎn)到多點(diǎn)的可靠性鏈接。媒介訪問(wèn)控制為數(shù)據(jù)傳輸建立通信鏈路，并提供對(duì)共享媒介的公平、有效的訪問(wèn)。它需要減少或避免媒介中的包沖突。

4、差錯(cuò)控制主要采用自動(dòng)重發(fā)請(qǐng)求（ARQ）和前向糾錯(cuò)（FEC）。 可靠性協(xié)議網(wǎng)絡(luò)層 建立局部多路徑可靠性協(xié)議網(wǎng)絡(luò)層 定向洪泛Sink NodeVirtual ApertureSenderBA可靠性協(xié)議 傳輸層事件匯聚到Sink可靠性協(xié)議傳輸層 - 從匯聚節(jié)點(diǎn)到傳感節(jié)點(diǎn)的傳輸 PSFQ（Pump Slowly, Fetch Quickly）為無(wú)線傳感器網(wǎng)絡(luò)的重編程或重新指定任務(wù)提供了可靠傳輸，并提供了到接收端延遲保證。源節(jié)點(diǎn)低速向網(wǎng)絡(luò)注入數(shù)據(jù)包以避免網(wǎng)絡(luò)擁塞，接收節(jié)點(diǎn)有足夠的時(shí)間來(lái)檢測(cè)這些數(shù)據(jù)包是否丟失，假如發(fā)生丟失就請(qǐng)求重傳。當(dāng)節(jié)點(diǎn)收到的包序號(hào)不等于上一個(gè)包序號(hào)加1，那么就認(rèn)為有包丟失。這個(gè)節(jié)點(diǎn)在

5、收到正確的包之前停止繼續(xù)發(fā)送包。 可靠性協(xié)議傳輸層 - 從匯聚節(jié)點(diǎn)到傳感節(jié)點(diǎn)的傳輸 PSFQ重傳機(jī)制 可靠性: 術(shù)語(yǔ) “可靠的”是涵蓋性術(shù)語(yǔ)主要指標(biāo) （穩(wěn)態(tài)的）可用性（穩(wěn)態(tài)的）可用性 probability that a system is operational at any given point in timeAssumption: System can fail and will repair itself在時(shí)間在時(shí)間t t的可靠性的可靠性 Probability that system works correctly during the entire interval 0,t)As

6、sumption: It worked correctly at system start t=0相應(yīng)速度相應(yīng)速度Responsiveness Responsiveness Probability of meeting a deadlineEven in presence of some to be defined faults 包成功的概率包成功的概率 Probability that a packet (correctly) reaches its destinationRelated: packet error rate, packet loss rate 誤碼率誤碼率Bit error

7、 rate Bit error rate Probability of an incorrect bitChannel model determines precise error patterns可靠性約束無(wú)線傳感器網(wǎng)絡(luò)為了可靠的傳輸數(shù)據(jù)需要考慮的約束條件：Transmission errors over a wireless channelLimited computational resources in a WSN nodeLimited memoryLimited time (deadlines)Limited dependability of individual nodes 機(jī)制

8、: 冗余Redundancy in nodes, transmissionForward and backward error recoveryCombinations are necessary!可靠的數(shù)據(jù)傳輸 背景 傳輸?shù)膶?duì)象Single packetBlock of packetsStream of packets保證水平Guaranteed deliveryStochastic delivery有關(guān)實(shí)體Involved entitiesSensor(s) to sinkSink to sensorsSensors to sensors50% delivered限制條件能量Send as

9、 few packets as possibleSend with low power ! high error ratesAvoid retransmissionsShort packets ! weak Forward Error Correction （FEC ）Balance energy consumption in network處理功率Only simple FEC schemesNo complicated algorithms (coding)存儲(chǔ)器Store as little data as briefly as possible Overview可靠性要求Deliver

10、ing single packetsDelivering single packetsSingle pathMultiple pathsGossiping-based approachesMultiple receiversDelivering blocks of packetsDelivering streams of packets傳遞單個(gè)數(shù)據(jù)包 主要選擇目的接收器是什么?單個(gè)接收器? 多個(gè)接收器?在周圍? 展開(kāi)?移動(dòng)的? 哪些路由結(jié)構(gòu)可用?Unicast routing along a single pathsingle path?Routing with multiple pathsm

11、ultiple paths between source/destination pairs? No routing structure at all rely on flooding/gossipingflooding/gossiping? 單個(gè)包經(jīng)過(guò)單個(gè)路徑到底單個(gè)接收器單個(gè)多跳路徑可由某一路由協(xié)議得到問(wèn)題: 哪個(gè)節(jié)點(diǎn)監(jiān)測(cè)丟包 (使用哪些指示器)? 要求重傳？執(zhí)行重傳？在單個(gè)包傳遞的時(shí)候檢測(cè)包或信令丟失檢測(cè)單個(gè)包丟失: 只有肯定確認(rèn) positive acknowledgements (ACK) 可行否定Negative acks (NACK) 不可行 接收機(jī)通常不知道哪個(gè)包應(yīng)該到底，不能

12、發(fā)NACK哪個(gè)節(jié)點(diǎn)發(fā)ACKs (以避免重傳)?在每個(gè)中間節(jié)點(diǎn)，在 MAC/link 層通常伴隨著鏈路層重傳通常有限定的重傳次數(shù)在目的節(jié)點(diǎn)傳輸層重傳問(wèn)題: 定時(shí)器選擇執(zhí)行重傳 鏈路層確認(rèn): 鄰居節(jié)點(diǎn) 傳輸層確認(rèn): 源節(jié)點(diǎn) ! 端到端的重傳Question: Could an intermediate node help in an end-to-end scheme? How to detect need for retransmissions? How to retransmit? Tradeoff: 端到端 vs. 鏈路層重傳 場(chǎng)景: 單個(gè)包,從源到目的節(jié)點(diǎn)經(jīng)過(guò)n 跳，二進(jìn)制對(duì)稱信道（ BS

13、C channel） 鏈路層，端到端重傳 鏈路層重傳: 最大重傳的次數(shù)是不同的 在其范圍內(nèi)仍然不成功就丟棄包 對(duì)于好的信道，使用端到端方案; 否則使用局部重傳 1 0 0 0 1 0 0 0 0 1 0 0 0 0 0 1 e + 0 6 1 e + 0 7 1 e - 0 6 1 e - 0 5 0 . 0 0 0 1 0 . 0 0 1 0 . 0 1B it e r r or pr o b a b i l i typ u r e e n d-to- e n dM A C 2 M A C 5 M A C 1 0 The BSC is a binary channel; that is, i

14、t can transmit only one of two symbols (usually called 0 and 1). The transmission is not perfect, and occasionally the receiver gets the wrong bit. 多個(gè)路徑 類型 : 不相交（disjoint） or 編織的（braided） 使用默認(rèn)的或可用的多條路徑 同時(shí) 發(fā)送相同的包 發(fā)送多余的片段 例子: ReInForM多路徑: 不相交或編織的SourceSinkDisjoint pathsPrimary pathSecondary pathSource

15、SinkBraided pathsPrimary path可靠數(shù)據(jù)傳輸造成數(shù)據(jù)包丟失的原因主要有三個(gè)方面：無(wú)線傳感器網(wǎng)絡(luò)所使用的無(wú)線信道較之有線鏈路有更大的不穩(wěn)定性以及更高的誤碼率，很容易受到周圍環(huán)境噪聲的影響造成數(shù)據(jù)包的丟失。另外在無(wú)線傳感器網(wǎng)絡(luò)中，傳感器節(jié)點(diǎn)的布撒密度非常高，不同節(jié)點(diǎn)在發(fā)送數(shù)據(jù)時(shí)極易發(fā)生信道競(jìng)爭(zhēng)沖突以及碰撞造成數(shù)據(jù)包丟失。當(dāng)無(wú)線傳感器網(wǎng)絡(luò)中發(fā)生擁塞時(shí)，擁塞節(jié)點(diǎn)緩沖區(qū)溢出造成數(shù)據(jù)包丟失。接收節(jié)點(diǎn)因?yàn)閿?shù)據(jù)包到達(dá)過(guò)快來(lái)不及處理造成數(shù)據(jù)包丟失。差錯(cuò)避免可靠傳輸單分組傳遞： Reliable Information Forwardingusing Multiple Paths in

16、Sensor Networks(ReInForM)Example: Reliable Information Forwardingusing Multiple Paths in Sensor Networks(ReInForM)目標(biāo): 通過(guò)多條路徑發(fā)送數(shù)據(jù)包來(lái)滿足傳遞概率P假設(shè): 獨(dú)立路徑,二進(jìn)制對(duì)稱信道BSC 節(jié)點(diǎn)知道本地的包錯(cuò)誤率eStep 1: 源節(jié)點(diǎn)決定使用哪些路徑Success probability over a single path with ns hops: 1-(1-e)ns Success probability over P paths: 1-(1-(1-e)ns)P

17、Should be rs, solve for P:Note there is no floor/ceiling in this formula ReInForM Forwarding to neighbors Source node picks a forwarderforwarder closer to destination than itselfRemaining neighbors: P = P (1-es)Choose P neighbors to additionally forward packetIf possible, only neighbors closer to de

18、stinationIf not sufficient, use neighbors same hop distanceIf not sufficient, use further away neighborsSourceDesti-nationForwarder Packet contains Source & destination Forwarder identity Source packet error rate Number of paths each neighbor should construct圖 ReInform所需傳送概率為70%時(shí)數(shù)據(jù)轉(zhuǎn)發(fā)舉例。(A)圖是源節(jié)點(diǎn)在

19、鏈路差錯(cuò)率為0時(shí)傳遞1個(gè)數(shù)據(jù)包；(B)圖是源節(jié)點(diǎn)在鏈路差錯(cuò)率為0時(shí)傳遞10個(gè)數(shù)據(jù)包；(C)是源節(jié)點(diǎn)在鏈路差錯(cuò)率為30%時(shí)傳遞1個(gè)數(shù)據(jù)包(D)是源節(jié)點(diǎn)在鏈路差錯(cuò)率為30%時(shí)發(fā)送10個(gè)單分組 圖 洪泛、單路徑轉(zhuǎn)發(fā)以及40%、70%可靠性要求的多路徑轉(zhuǎn)發(fā)在鏈路出錯(cuò)率增加時(shí)所能保證的可靠性比較 圖 洪泛、單路徑轉(zhuǎn)發(fā)以及40%、70%可靠性要求的多路徑轉(zhuǎn)發(fā)在鏈路出錯(cuò)率增加時(shí)為保證可靠性所引發(fā)的開(kāi)銷 OverviewDependability requirementsDelivering single packetsDelivering blocks of packetsDelivering blocks

20、 of packetsOpportunity: Caching in intermediate nodesExample: Pump Slowly, Fetch Quickly (PSFQ)Example: Reliable Multisegment Transport (RMST) Delivering streams of packets數(shù)據(jù)塊傳輸數(shù)據(jù)塊傳輸Goal: Deliver large amounts of dataE.g., code update, large observationsSplit data into several packets (reduce packet

21、 error rate)Transfer this block of packets Main difference to single packet delivery: Gaps in sequence number can be detected and exploitedFor example, by intermediate nodes sending NACKs1 3 2Whereis packet 2?2? To answer NACK locally, intermediate nodes must cache packets Which packets? For how lon

22、g?數(shù)據(jù)塊傳輸在無(wú)線傳感器網(wǎng)絡(luò)中，無(wú)線鏈路不穩(wěn)定及易受干擾的特點(diǎn)是造成網(wǎng)絡(luò)傳輸不可靠的主要原因.除了在物理層實(shí)現(xiàn)高效的糾錯(cuò)碼之外，如何在MAC層、傳輸層以及應(yīng)用層提供可靠性是實(shí)現(xiàn)可靠傳輸?shù)闹匾ＷC。 在MAC層實(shí)現(xiàn)可靠性保證的重要性體現(xiàn)在，它除了能為傳輸層提供跳段之間的錯(cuò)誤恢復(fù)之外，還是實(shí)現(xiàn)路由發(fā)現(xiàn)及維持的保證。 數(shù)據(jù)塊傳輸:RMST每跳鏈路出錯(cuò)率為10%，數(shù)據(jù)傳輸 40跳時(shí)，傳輸成功概率數(shù)據(jù)塊傳輸:RMST數(shù)據(jù)傳輸6跳時(shí)，傳輸成功概率比較 數(shù)據(jù)塊傳輸802.11中提供了數(shù)據(jù)包分片與重組的方法，但是并沒(méi)有提供傳輸可靠性保證。而傳統(tǒng)有線網(wǎng)絡(luò)中的傳輸層TCP協(xié)議提供的傳輸可靠保證主要是為解決網(wǎng)絡(luò)擁

23、塞問(wèn)題而提出的，并不適用于無(wú)線網(wǎng)絡(luò)。數(shù)據(jù)塊傳輸端到端選擇請(qǐng)求NACK是當(dāng)基站節(jié)點(diǎn)發(fā)現(xiàn)接收的數(shù)據(jù)包有丟失或損壞時(shí)，沿著基站到源節(jié)點(diǎn)的反向增強(qiáng)路徑發(fā)送重傳請(qǐng)求。當(dāng)重傳請(qǐng)求到達(dá)源節(jié)點(diǎn)后，源節(jié)點(diǎn)將重傳所需數(shù)據(jù)。端到端選擇請(qǐng)求NACK方法只需在基站和源節(jié)點(diǎn)緩存數(shù)據(jù)，中間節(jié)點(diǎn)無(wú)需緩存數(shù)據(jù)。跳段選擇請(qǐng)求NACK方法是在路由路徑上的每個(gè)節(jié)點(diǎn)都緩存數(shù)據(jù)，當(dāng)節(jié)點(diǎn)發(fā)現(xiàn)有數(shù)據(jù)包丟或損壞時(shí)直接向其上一跳節(jié)點(diǎn)發(fā)送重傳請(qǐng)求。Example: Pump Slowly Fetch Quickly (PSFQ)Goal: Distribute block of packets to from one sender to mult

24、iple receivers (sink to sensors)E.g., code update ! losses are not tolerable, delay not critical Routing structure is assumed to be known PSFQ（Pump Slowly, Fetch Quickly）為無(wú)線傳感器網(wǎng)絡(luò)的重編程或重新指定任務(wù)提供了可靠傳輸，并提供了到接收端延遲保證。源節(jié)點(diǎn)低速向網(wǎng)絡(luò)注入數(shù)據(jù)包以避免網(wǎng)絡(luò)擁塞，接收節(jié)點(diǎn)有足夠的時(shí)間來(lái)檢測(cè)這些數(shù)據(jù)包是否丟失，假如發(fā)生丟失就請(qǐng)求重傳。當(dāng)節(jié)點(diǎn)收到的包序號(hào)不等于上一個(gè)包序號(hào)加1，那么就認(rèn)為有包丟失。這個(gè)節(jié)

25、點(diǎn)在收到正確的包之前停止繼續(xù)發(fā)送包。Overview傳輸層 - 從匯聚節(jié)點(diǎn)到傳感節(jié)點(diǎn)的傳輸 PSFQ重傳機(jī)制 OverviewDependability requirementsDelivering single packetsDelivering blocks of packetsDelivering streams of packetsDelivering streams of packetsAdditional opportunity: Control rateControl rate of individual nodes: ESRTControl number of active n

26、odes: Gur gameStreams of packets may lead to congestionWhen several sensors observe an event and try to periodically report it, congestion around event may set itWhen many sensors stream data to a sink, congestion around the sink may occur擁塞控制無(wú)線傳感器網(wǎng)絡(luò)大部分時(shí)間都處于零負(fù)載或輕負(fù)載，只有在異常事件發(fā)生時(shí)，網(wǎng)絡(luò)中才會(huì)突發(fā)性的產(chǎn)生較大的數(shù)據(jù)量。這些數(shù)據(jù)非常重要，需要在不影響系統(tǒng)性能的前提下可靠的傳送給基站。但是這種突發(fā)性的大數(shù)據(jù)量傳輸很容易導(dǎo)網(wǎng)絡(luò)不同程度擁塞的發(fā)生。網(wǎng)絡(luò)吞吐量隨源速率的增加而減小.節(jié)點(diǎn)數(shù)量越大，實(shí)際吞吐量減少的越大. 擁塞檢測(cè)和避免（ CODA ）擁塞控制方案擁塞場(chǎng)景 :(1)節(jié)點(diǎn)密集分布的網(wǎng)絡(luò)中，當(dāng)有異常事件發(fā)生時(shí)，源節(jié)點(diǎn)會(huì)突發(fā)性產(chǎn)生大量數(shù)據(jù)。在源節(jié)點(diǎn)附近(幾跳范圍內(nèi))形成持續(xù)擁塞區(qū)域。 (2)在節(jié)點(diǎn)分布稀疏并且源節(jié)點(diǎn)數(shù)據(jù)發(fā)送速率較低的網(wǎng)絡(luò)中，不會(huì)在源節(jié)點(diǎn)附近產(chǎn)生持續(xù)的擁塞，而可