无线终端自主形成通信网络AdHocMode和DelayTolerateNetwork课件.ppt

1、无线网络 3G标准 Bluetooth WiFi3G3G：全称为3rd Generation，中文含义就是指第三代数字通信。1995年问世的第一代模拟制式手机（1G）只能进行语音通话(FDMA)；1996到1997年出现的第二代GSM、TDMA等数字制式手机（2G）便增加了接收数据的功能，如接收电子邮件或网页；国际电联ITU在2000年5月确定WCDMA、CDMA2000、TD-SCDMA以及WiMAX四大主流无线接口标准，写入3G技术指导性文件2000年国际移动通讯计划（简称IMT2000）3G WCDMA，全称为Wideband CDMA，也称为CDMA Direct Spread，意为宽

2、频码分多路存取，这是基于GSM网发展出来的3G技术规范，是欧洲提出的宽带CDMA技术，它与日本提出的宽带CDMA技术基本相同，目前正在进一步融合。CDMA2000是由窄带CDMA(CDMA IS95)技术发展而来的宽带CDMA技术，也称为CDMA Multi-Carrier，它是由美国高通北美公司为主导提出，摩托罗拉、Lucent和后来加入的韩国三星都有参与，韩国现在成为该标准的主导者。3G Time Division-Synchronous CDMA(时分同步CDMA)，该标准是由中国大陆独自制定的3G标准，1999年6月29日，中国原邮电部电信科学技术研究院（大唐电信）向ITU提出。该标准

3、将智能无线、同步CDMA和软件无线电等当今国际领先技术融于其中，在频谱利用率、对业务支持具有灵活性、频率灵活性及成本等方面的独特优势。WiMAX 的全名是微波存取全球互通(Worldwide Interoperability for Microwave Access)，又称为802.16无线城域网，是又一种为企业和家庭用户提供“最后一英里”的宽带无线连接方案。2007年10月19日，WiMAX正式被批准成为继WCDMA、CDMA2000和TD-SCDMA之后的第四个全球3G标准。Bluetooth Bluetooth 技术在 2.4 GHz 波段运行，该波段是一种无需申请许可证的工业、科技、医

4、学(ISM)无线电波段；蓝牙目前暂时共有四个版本 V1.1/1.2/2.0/2.1；以通讯距离可分为 Class A(1)/Class B(2)，ClassA通讯距离大约在 80100M 距离之间，ClassB 830M 之间；UWB超宽带版本，版本于2008年中发布。整合了UWB技术的新版蓝牙将使用户能够对大量数据同速进行和传输，UWB技术在10米的有效范围内速率可达到480Mbps，超过了许多应用中最高要求的200Mbps，将MP3播放器或高画质数码相机的同速进行即是此技术的应用实例。Wireless Networking(802.11)wifi常见标准有以下几种常见标准有以下几种：IEE

5、E 802.11a：使用5GHz频段，传输速度54Mbps，与802.11b不兼容 IEEE 802.11b：使用2.4GHz频段，传输速度11Mbps IEEE 802.11g：使用2.4GHz频段，传输速度主要有54Mbps、108Mbps，可向下兼容802.11b IEEE 802.11n草案：使用2.4GHz频段，传输速度可达300Mbps，目前标准尚为草案，但产品已层出不穷目前IEEE 802.11b最常用，但IEEE 802.11g更具下一代标准的实力，802.11n也在快速发展中。Overview Physical layer Link layer challenges Inte

6、rnet mobilityPhysical layer 规定工作频段规定工作频段 数据收发时的调制方法数据收发时的调制方法Cellular Reuse Transmissions decay over distance Spectrum can be reused in different areas Different“LANs”Decay is 1/R2 in free space,1/R4 in some situationsOverview Physical layer Link layer challenges Internet mobilityWiFi工作模式从形成的无线网络是否存

7、在中心访问节点来看，分为机会网络（Opportunity Network）和基础设施网络（Infrastructure Network）两种类型。机会网络（Opportunity Network）无线终端自主形成通信网络无线终端自主形成通信网络Ad Hoc Mode Ad Hoc Mode 和和 Delay Tolerate NetworkDelay Tolerate NetworkCSMA/CD Does Not Work Carrier sense problems Relevant contention at the receiver,not sender Hidden terminal

8、 Exposed terminal A B CMedia access control(a)The hidden station problem.(b)The exposed station problem.CSMA/CAWhy not use CSMA/CD?MACA Multiple Access Collision Avoidance Sender send RTS(require to send)with a time to use the radio media Receiver send CTS(clear to send)to sender Any other terminal

9、who get the CTS will not send data Multi-RTS Collision：Senders cant receive the CTSMACA工作模式（基础设施模式）无线终端通过无线终端通过APAP接入有线网络接入有线网络 Infrastructure ModeInfrastructure ModeAP Finding-Active Scanning Host broadcast Probe All APs which get that Probe return a Probe Response Host select a AP as its associate

10、 AP and send Association Request The selected AP returns a Associate ResponseOverview Physical layer Link layer challenges Internet mobility(Mobility IP)Mobility IP Addressing Dynamic Host Configuration(DHCP)Host gets new IP address in new locations Problems Host does not have constant name/address

11、how do others contact host Naming Use DHCP and update name-address mapping whenever host changes addressMobile IP(RFC 2290)Interception Typically home agent hosts on home network Delivery Typically IP-in-IP tunneling Endpoint either temporary mobile address or foreign agent Terminology Mobile host(M

12、H),correspondent host(CH),home agent(HA),foreign agent(FA)home addressMobile IP(MH at Home)Mobile Host(MH)Visiting LocationHomeInternetCorrespondent Host(CH)PacketMobile IP(MH Moving)Visiting LocationHomeInternetCorrespondent Host(CH)PacketHome Agent(HA)Mobile Host(MH)I am hereMobile IP(MH Away Fore

13、ign Agent)Visiting LocationHomeInternetCorrespondent Host(CH)PacketHome Agent(HA)Foreign Agent(FA)EncapsulatedMobile Host(MH)Overview Physical layer Link layer challenges Internet mobility 无线网络的传输距离与那些因素相关?802.11b的蜂窝半径？3G标准中三种标准（TD-SCDMA,WCDMA,CDMA2000)的工作频段？The end of wireless ENDChallenge#1:Wirele

14、ss Bit-ErrorsRouterComputer 2Computer 12 32 22 10Burst losses lead to coarse-grained timeoutsResult:Low throughputWirelessPerformance Degradation0.0E+005.0E+051.0E+061.5E+062.0E+060102030405060Time(s)Sequence number(bytes)TCP Reno(280 Kbps)Best possible TCP with no errors(1.30 Mbps)2 MB wide-area TC

15、P transfer over 2 Mbps Lucent WaveLANProposed Solutions End-to-end protocols Selective ACKs,Explicit loss notification Split-connection protocols Separate connections for wired path and wireless hop Reliable link-layer protocols Error-correcting codes Local retransmissionApproach Styles(End-to-End)I

16、mprove TCP implementations Not incrementally deployable Improve loss recovery(SACK,NewReno)Help it identify congestion(ELN,ECN)ACKs include flag indicating wireless loss Trick TCP into doing right thing E.g.send extra dupacksWired linkWireless linkEnd-to-End:Selective AcksCorrespondent HostMobile Ho

17、stBase Station51346X2End-to-End:Selective AcksCorrespondent HostMobile HostBase Stationack 1ack 1,3 ack 1,3-4 ack 1,3-5 ack 1,3-6 Approach Styles(Split Connection)Split connections Wireless connection need not be TCP Hard state at base station Complicates mobility Vulnerable to failures Violates end

18、-to-end semanticsWired linkWireless linkSplit ConnectionCorrespondent HostMobile HostBase Station2AB3X1ack 0ack 0 Xsack Asack A,B Csack A,B,D DSplit-Connection Congestion WindowWired connection does not shrink congestion window But wireless connection times out often,causing sender to stall010000200

19、0030000400005000060000020406080100120Time(sec)Congestion Window(bytes)Wired connectionWireless connectionApproach Styles(Link Layer)More aggressive local rexmit than TCP Bandwidth not wasted on wired links Adverse interactions with transport layer Timer interactions Interactions with fast retransmis

20、sions Large end-to-end round-trip time variation FEC does not work well with burst lossesWired linkWireless linkARQ/FECHybrid Approach:Snoop Protocol Transport-aware link protocol Modify base station To cache un-acked TCP packets And perform local retransmissions Key ideas No transport level code in

21、 base station When node moves to different base station,state eventually recreated thereSnoop Protocol:CH to MHCorrespondent HostMobile HostBase Station5112346 Snoop agent:active interposition agent Snoops on TCP segments and ACKs Detects losses by duplicate ACKs and timers Suppresses duplicate ACKs

22、 from FH senderSnoop AgentSnoop Protocol:CH to MHCorrespondent HostMobile HostBase Station Transfer of file from CH to MH Current window=6 packetsSnoop Agent654321Snoop Protocol:CH to MHCorrespondent HostMobile HostBase Station Transfer beginsSnoop Agent654321Snoop Protocol:CH to MHCorrespondent Hos

23、tMobile HostBase Station5112346 Snoop agent caches segments that pass by Difference#1 from pure link-layer does not add a new header uses existing TCP header to identify lossesSnoop AgentSnoop Protocol:CH to MHCorrespondent HostMobile HostBase Station512346 Packet 1 is LostSnoop Agent231Lost Packets

24、1Snoop Protocol:CH to MHCorrespondent HostMobile HostBase Station512346 Packet 1 is Lost Duplicate ACKs generatedSnoop Agent23Lost Packets14ack 0Snoop Protocol:CH to MHCorrespondent HostMobile HostBase Station512346 Packet 1 is Lost Duplicate ACKs generated Packet 1 retransmitted from cache at highe

25、r prioritySnoop Agent23Lost Packets14ack 0561ack 0Snoop Protocol:CH to MHCorrespondent HostMobile HostBase Station512346 Duplicate ACKs suppressed Difference#2 from pure link-layer tries to prevent sender from noticing loss Sender may still timeout though fortunately timeouts are typically long(500m

26、s+)Snoop Agent234ack 4561ack 0XSnoop Protocol:CH to MHCorrespondent HostMobile HostBase Station56 Clean cache on new ACKSnoop Agent234ack 5615ack 4Snoop Protocol:CH to MHCorrespondent HostMobile HostBase Station6 Clean cache on new ACKSnoop Agent234ack 6156ack 5ack 4Snoop Protocol:CH to MHCorrespond

27、ent HostMobile HostBase Station Active soft state agent at base station Transport-aware reliable link protocol Preserves end-to-end semanticsSnoop Agent234ack 6156978ack 5Snoop Data ProcessingYesPacket arrivesNew pkt?No1.Forward pkt2.Reset local rexmit counterIn-sequence?Yes1.Cache packet2.Forward t

28、o mobile1.Mark as cong.loss2.Forward pktCongestion lossCommon caseSender retransmissionNoSnoop ACK ProcessingNoDup ack?NoNew ack?Yes1.Free buffers2.Update RTT estimateYesDiscard thresholdNoDiscardRetransmitYeslost packet3.Propagate ack to senderCommon caseSpurious ackNext pkt lostLater dup acks for

29、lost packetAck arrives(from mobile host)Overview Link layer challenges Internet mobility TCP Over Noisy Links Adapting Applications to Slow LinksAdapting Applications Applications make key assumptions Hardware variation E.g.how big is screen?Software variation E.g.is there a postscript decoder?Netwo

30、rk variation E.g.how fast is the network?Reason why we are discussing in this class Basic idea distillation Transcode object to meet needs of mobile hostTranscoding Example Generate reduced quality variant of Web page at proxy Must predict how much size reduction will result from transcoding How long to transcode?Send appropriate reduced-size variant Target response time?Source Adaptation Can also just have source provide different versions Common solution today No waiting for transcoding Full version not sent across network Cant handle fine grain adaptation