15-441socketprogramming

1、無線網(wǎng)絡(luò),3G標(biāo)準(zhǔn)BluetoothWiFi,3G,3G：全稱為3rd Generation，中文含義就是指第三代數(shù)字通信。1995年問世的第一代模擬制式手機（1G）只能進行語音通話(FDMA)；1996到1997年出現(xiàn)的第二代GSM、TDMA等數(shù)字制式手機（2G）便增加了接收數(shù)據(jù)的功能，如接收電子郵件或網(wǎng)頁；國際電聯(lián)ITU在2000年5月確定WCDMA、CDMA2000、TD-SCDMA以及WiMAX四大主流無線接口標(biāo)準(zhǔn)，寫

2、入3G技術(shù)指導(dǎo)性文件《2000年國際移動通訊計劃》（簡稱IMT—2000）,3G,WCDMA，全稱為Wideband CDMA，也稱為CDMA Direct Spread，意為寬頻碼分多路存取，這是基于GSM網(wǎng)發(fā)展出來的3G技術(shù)規(guī)范，是歐洲提出的寬帶CDMA技術(shù)，它與日本提出的寬帶CDMA技術(shù)基本相同，目前正在進一步融合。CDMA2000是由窄帶CDMA(CDMA IS95)技術(shù)發(fā)展而來的寬帶CDMA技術(shù)，也稱為CDMA Multi-

3、Carrier，它是由美國高通北美公司為主導(dǎo)提出，摩托羅拉、Lucent和后來加入的韓國三星都有參與，韓國現(xiàn)在成為該標(biāo)準(zhǔn)的主導(dǎo)者。,3G,Time Division - Synchronous CDMA(時分同步CDMA)，該標(biāo)準(zhǔn)是由中國大陸?yīng)氉灾贫ǖ?G標(biāo)準(zhǔn)，1999年6月29日，中國原郵電部電信科學(xué)技術(shù)研究院（大唐電信）向ITU提出。該標(biāo)準(zhǔn)將智能無線、同步CDMA和軟件無線電等當(dāng)今國際領(lǐng)先技術(shù)融于其中，在頻譜利用率、對業(yè)務(wù)支持具有靈

4、活性、頻率靈活性及成本等方面的獨特優(yōu)勢。WiMAX 的全名是微波存取全球互通(Worldwide Interoperability for Microwave Access)，又稱為802.16無線城域網(wǎng)，是又一種為企業(yè)和家庭用戶提供“最后一英里”的寬帶無線連接方案。2007年10月19日，WiMAX正式被批準(zhǔn)成為繼WCDMA、CDMA2000和TD-SCDMA之后的第四個全球3G標(biāo)準(zhǔn)。,Bluetooth,Bluetooth 技術(shù)在

5、 2.4 GHz 波段運行，該波段是一種無需申請許可證的工業(yè)、科技、醫(yī)學(xué) (ISM) 無線電波段； 藍牙目前暫時共有四個版本 V1.1/1.2/2.0/2.1；以通訊距離可分為 Class A(1)/Class B(2)，ClassA通訊距離大約在 80~100M 距離之間，ClassB 8~30M 之間；UWB超寬帶版本，版本于2008年中發(fā)布。整合了UWB技術(shù)的新版藍牙將使用戶能夠?qū)Υ罅繑?shù)據(jù)同速進行和傳輸，UWB技術(shù)在10

6、米的有效范圍內(nèi)速率可達到480Mbps，超過了許多應(yīng)用中最高要求的200Mbps，將MP3播放器或高畫質(zhì)數(shù)碼相機的同速進行即是此技術(shù)的應(yīng)用實例。,Wireless Networking(802.11),,wifi常見標(biāo)準(zhǔn)有以下幾種： 　IEEE 802.11a ：使用5GHz頻段，傳輸速度54Mbps，與802.11b不兼容 IEEE 802.11b ：使用2.4GHz頻段，傳輸速度11Mbps IEEE 802.11g ：使

7、用2.4GHz頻段，傳輸速度主要有54Mbps、108Mbps，可向下兼容802.11b IEEE 802.11n草案：使用2.4GHz頻段，傳輸速度可達300Mbps，目前標(biāo)準(zhǔn)尚為草案，但產(chǎn)品已層出不窮目前IEEE 802.11b最常用，但IEEE 802.11g更具下一代標(biāo)準(zhǔn)的實力，802.11n也在快速發(fā)展中。,Overview,Physical layerLink layer challengesInternet

8、 mobility,Physical layer,規(guī)定工作頻段數(shù)據(jù)收發(fā)時的調(diào)制方法,,Cellular Reuse,Transmissions decay over distanceSpectrum can be reused in different areasDifferent “LANs”Decay is 1/R2 in free space, 1/R4 in some situations,,,,,,,,,,,,,,,,

9、,,,,,Overview,Physical layerLink layer challengesInternet mobility,WiFi工作模式,從形成的無線網(wǎng)絡(luò)是否存在中心訪問節(jié)點來看，分為機會網(wǎng)絡(luò)（Opportunity Network）和基礎(chǔ)設(shè)施網(wǎng)絡(luò)（Infrastructure Network）兩種類型。,機會網(wǎng)絡(luò)（Opportunity Network ）,,無線終端自主形成通信網(wǎng)絡(luò)Ad Hoc Mode 和

10、 Delay Tolerate Network,CSMA/CD Does Not Work,Carrier sense problemsRelevant contention at the receiver, not senderHidden terminalExposed terminal,A,B,C,Media access control,(a) The hidden station problem.(b) The exp

11、osed station problem.,CSMA/CA,Why not use CSMA/CD?,MACA,Multiple Access Collision AvoidanceSender send RTS (require to send) with a time to use the radio mediaReceiver send CTS (clear to send) to senderAny other termi

12、nal who get the CTS will not send data Multi-RTS Collision： Senders can’t receive the CTS,MACA,工作模式（基礎(chǔ)設(shè)施模式）,,無線終端通過AP接入有線網(wǎng)絡(luò) Infrastructure Mode,AP Finding-Active Scanning,Host broadcast ProbeAll APs which get that Pr

13、obe return a Probe ResponseHost select a AP as its associate AP and send Association RequestThe selected AP returns a Associate Response,Overview,Physical layerLink layer challengesInternet mobility (Mobility IP),M

14、obility IP Addressing,Dynamic Host Configuration (DHCP)Host gets new IP address in new locationsProblemsHost does not have constant name/address ? how do others contact hostNamingUse DHCP and update name-address map

15、ping whenever host changes address,Mobile IP (RFC 2290),InterceptionTypically home agent – hosts on home networkDeliveryTypically IP-in-IP tunnelingEndpoint – either temporary mobile address or foreign agentTerminol

16、ogyMobile host (MH), correspondent host (CH), home agent (HA), foreign agent (FA)home address,,,,Mobile IP (MH at Home),Mobile Host (MH),Visiting Location,Home,Internet,Correspondent Host (CH),,,,Packet,,,,Mobile IP (M

17、H Moving),Visiting Location,Home,Internet,Correspondent Host (CH),,,Packet,Home Agent (HA),,Mobile Host (MH),,,I am here,,,,Mobile IP (MH Away – Foreign Agent),Visiting Location,Home,Internet,Correspondent Host (CH),,,,P

18、acket,,,Home Agent (HA),Foreign Agent (FA),Encapsulated,,Mobile Host (MH),Overview,Physical layerLink layer challengesInternet mobility,,無線網(wǎng)絡(luò)的傳輸距離與那些因素相關(guān)? 802.11b的蜂窩半徑？3G標(biāo)準(zhǔn)中三種標(biāo)準(zhǔn)（TD-SCDMA,WCDMA,CDMA2000)的工作頻段？,The en

19、d of wireless,END,Challenge #1: Wireless Bit-Errors,,Router,Computer 2,Computer 1,Burst losses lead to coarse-grained timeouts,Result: Low throughput,,,Wireless,,,Performance Degradation,Time (s),Sequence number (bytes),

20、TCP Reno(280 Kbps),Best possible TCP with no errors(1.30 Mbps),2 MB wide-area TCP transfer over 2 Mbps Lucent WaveLAN,Proposed Solutions,End-to-end protocolsSelective ACKs, Explicit loss notificationSplit-connection

21、 protocolsSeparate connections for wired path and wireless hopReliable link-layer protocolsError-correcting codesLocal retransmission,Approach Styles (End-to-End),Improve TCP implementationsNot incrementally deploya

22、bleImprove loss recovery (SACK, NewReno)Help it identify congestion (ELN, ECN)ACKs include flag indicating wireless lossTrick TCP into doing right thing ? E.g. send extra dupacks,,,Wired link,Wireless link,,,End-to-E

23、nd: Selective Acks,,,Correspondent Host,Mobile Host,Base Station,,,,,,,3,,X,2,,End-to-End: Selective Acks,,,Correspondent Host,Mobile Host,Base Station,,,,,,ack 1,ack 1,3,ack 1,3-4,ack 1,3-5,ack 1,3-6,,,Approach Styles (

24、Split Connection),Split connectionsWireless connection need not be TCPHard state at base stationComplicates mobilityVulnerable to failuresViolates end-to-end semantics,Wired link,Wireless link,,,Split Connection,,,C

25、orrespondent Host,Mobile Host,Base Station,,,,B,,,,,X,1,ack 0,ack 0,,X,sack A,sack A,B,,C,sack A,B,D,,D,,Split-Connection Congestion Window,Wired connection does not shrink congestion window But wireless connection time

26、s out often, causing sender to stall,Approach Styles (Link Layer),More aggressive local rexmit than TCPBandwidth not wasted on wired linksAdverse interactions with transport layerTimer interactionsInteractions with f

27、ast retransmissionsLarge end-to-end round-trip time variationFEC does not work well with burst losses,,,Wired link,Wireless link,,ARQ/FEC,Hybrid Approach: Snoop Protocol,Transport-aware link protocolModify base statio

28、n To cache un-acked TCP packets … And perform local retransmissionsKey ideasNo transport level code in base stationWhen node moves to different base station, state eventually recreated there,,Snoop Protocol: CH to M

29、H,,,Correspondent Host,Mobile Host,Base Station,,,,1,,,2,,,3,Snoop agent: active interposition agentSnoops on TCP segments and ACKsDetects losses by duplicate ACKs and timersSuppresses duplicate ACKs from FH sender,Sn

30、oop Agent,,,,Snoop Protocol: CH to MH,,,Correspondent Host,Mobile Host,Base Station,,Transfer of file from CH to MHCurrent window = 6 packets,Snoop Agent,,,6,5,4,3,2,,,Snoop Protocol: CH to MH,,,Correspondent Host,Mobil

31、e Host,Base Station,,Transfer begins,Snoop Agent,,,6,5,4,3,2,,,Snoop Protocol: CH to MH,,,Correspondent Host,Mobile Host,Base Station,,,,1,,,2,,,3,Snoop agent caches segments that pass byDifference #1 from pure link-lay

32、er – does not add a new header uses existing TCP header to identify losses,Snoop Agent,,,,Snoop Protocol: CH to MH,,,Correspondent Host,Mobile Host,Base Station,,,,,1,,,2,,,3,Packet 1 is Lost,Snoop Agent,,,,,,2,,,3,Lost

33、Packets,,1,,Snoop Protocol: CH to MH,,,Correspondent Host,Mobile Host,Base Station,,,,,1,,,2,,,3,Packet 1 is LostDuplicate ACKs generated,Snoop Agent,,,,,,2,,,3,Lost Packets,,1,ack 0,,Snoop Protocol: CH to MH,,,Correspo

34、ndent Host,Mobile Host,Base Station,,,,,1,,,2,,,3,Packet 1 is LostDuplicate ACKs generatedPacket 1 retransmitted from cache at higher priority,Snoop Agent,,,,,,2,,,3,Lost Packets,,1,ack 0,ack 0,,Snoop Protocol: CH to M

35、H,,,Correspondent Host,Mobile Host,Base Station,,,,,1,,,2,,,3,Duplicate ACKs suppressedDifference #2 from pure link-layer – tries to prevent sender from noticing lossSender may still timeout though – fortunately timeou

36、ts are typically long (500ms+),Snoop Agent,,,,,,2,,,3,ack 4,ack 0,X,,Snoop Protocol: CH to MH,,,Correspondent Host,Mobile Host,Base Station,,,,,,Clean cache on new ACK,Snoop Agent,,,,,,2,,,3,ack 5,ack 4,,Snoop Protocol:

37、CH to MH,,,Correspondent Host,Mobile Host,Base Station,,,Clean cache on new ACK,Snoop Agent,,,,,,2,,,3,ack 6,ack 5,ack 4,,Snoop Protocol: CH to MH,,,Correspondent Host,Mobile Host,Base Station,,,Active soft state agent a

38、t base station Transport-aware reliable link protocol Preserves end-to-end semantics,Snoop Agent,,,,,,2,,,3,ack 6,ack 5,,Snoop Data Processing,Yes,,,,,Packet arrives,,,,,New pkt?,,,,,No,,,,,,,,,1. Forward pkt,2. Reset

39、local rexmit,counter,In-sequence?,,,,,Yes,1. Cache packet,2. Forward to,mobile,,,,,1. Mark as cong. loss,2. Forward pkt,Congestion loss,Common case,,,,,Sender retransmission,,,,,No,,Snoop ACK Processing,,,No,Dup ack?,,,,

40、,No,,,New ack?,,,,,Yes,1. Free buffers,2. Update,RTT estimate,,,,,Yes,,,,,,,,,,,,,Discard,,,,,,,> threshold,No,,,,,Discard,,,,,,,,,Retransmit,Yes,lost packet,3. Propagate,ack to sender,Common case,Spurious ack,Next pk

41、t lost,Later dup acks,for lost packet,,,,,Ack arrives (from mobile host),Overview,Link layer challengesInternet mobilityTCP Over Noisy LinksAdapting Applications to Slow Links,Adapting Applications,Applications mak

42、e key assumptionsHardware variationE.g. how big is screen?Software variationE.g. is there a postscript decoder?Network variationE.g. how fast is the network?Reason why we are discussing in this class ?Basic idea

43、– distillationTranscode object to meet needs of mobile host,Transcoding Example,,Generate reduced quality variant of Web page at proxyMust predict how much size reduction will result from transcodingHow long to transc

44、ode?Send appropriate reduced-size variantTarget response time?,Source Adaptation,,Can also just have source provide different versionsCommon solution todayNo waiting for transcodingFull version not sent across netwo