Chapter6_4th_ed

1、6: Wireless and Mobile Networks6-1Chapter 6Wireless and Mobile NetworksA note on the use of these ppt slides:Were making these slides freely available to all (faculty, students, readers). Theyre in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to su

2、it your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:q If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, wed like people to use our book!)q If you post any slides in substan

3、tially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and note our copyright of this material.Thanks and enjoy! JFK/KWRAll material copyright 1996-2007J.F Kurose and K.W. Ross, All Rights ReservedComputer Networking: A Top Down Approach 4

4、th edition. Jim Kurose, Keith RossAddison-Wesley, July 2007. 6: Wireless and Mobile Networks6-2Chapter 6 outline6.1 Introduction Wirelessr6.2 Wireless links, characteristicsmCDMAr6.3 IEEE 802.11 wireless LANs (“wi-fi”)r6.4 Cellular Internet Accessmarchitecturemstandards (e.g., GSM)Mobilityr6.5 Princ

5、iples: addressing and routing to mobile usersr6.6 Mobile IPr6.7 Handling mobility in cellular networksr6.8 Mobility and higher-layer protocols6.9 Summary6: Wireless and Mobile Networks6-3Chapter 6: 无线与移动网络背景: r无线电话使用者的数量已经超过了有线电话使用者的数量!r计算机网络: 笔记本, 掌上型电脑, PDAs, 可以访问Internet 的电话需要随时可用的、无固定接入位置的 Inter

6、net 访问r两个重要的 (但不相同的) 挑战m无线: 通过无线链路进行通信m移动性: 解决移动用户改变连接到网络的连接点的问题6: Wireless and Mobile Networks6-4无线网络的构成要素network infrastructure无线主机rlaptop, PDA, IP phoner运行应用程序r可以是固定的或移动的m无线并不一定意味着移动性6: Wireless and Mobile Networks6-5无线网络的构成要素network infrastructure 基站r通常与有线网络连接r中继 负责为处在其区域内的有线和无线主机间me.g., 蜂窝电话基站,

7、 802.11 接入点6: Wireless and Mobile Networks6-6无线网络的构成要素network infrastructure 无线链路r通常用于连接移动终端和基站r也用作主干网连接r使用多路访问协议协调链路访问 r不同的传输速率和传输距离6: Wireless and Mobile Networks6-7部分无线链路标准的特性Indoor10-30mOutdoor50-200mMid-rangeoutdoor200m 4 KmLong-rangeoutdoor5Km 20 Km.056.384145-1154IS-95, CDMA, GSM2GUMTS/WCDMA,

8、 CDMA20003G802.15802.11b802.11a,gUMTS/WCDMA-HSPDA, CDMA2000-1xEVDO3G cellularenhanced802.16 (WiMAX)802.11a,g point-to-point200802.11nData rate (Mbps)data6: Wireless and Mobile Networks6-8无线网络的构成要素network infrastructure基础设施模式r基站将移动终端连接到有线网络r切换: 移动终端改变接入有线网络的基站6: Wireless and Mobile Networks6-9无线网络的构成

9、要素自组网模式r不存在基站r节点间只能与连接范围内进行传输r节点自组织网络：在节点间自主安排路由6: Wireless and Mobile Networks6-10无线网络分类单跳多跳有基础设施(e.g., APs)无基础设施host connects to base station (WiFi,WiMAX, cellular) which connects to larger Internetno base station, noconnection to larger Internet (Bluetooth, ad hoc nets)host may have torelay throu

10、gh severalwireless nodes to connect to larger Internet: mesh netno base station, noconnection to larger Internet. May have torelay to reach other a given wireless nodeMANET, VANET6: Wireless and Mobile Networks6-11无线链路特性 (1)与有线链路的差异 .m信号强度衰减: 无线电信号随着传播距离的扩展变弱 (路径损耗)m其他源的干扰: 标准无线网络频率 (e.g., 2.4 GHz)

11、是设备共享的 (e.g., phone); 设备间互相干扰m多径传播: 无线电信号在物体表面反射，到达目的地的存在轻微的时间差异. 通过无线链路进行通信 (哪怕只是一个节点到另一个节点)困难得多 6: Wireless and Mobile Networks6-12无线链路特性多个无线发送方和接收方带来额外的问题 (不止是多路访问):ABC隐藏终端问题rB, A hear each otherrB, C hear each otherrA, C can not hear each othermeans A, C unaware of their interference at BABCAs s

12、ignalstrengthspaceCs signalstrength信号衰减:rB, A hear each otherrB, C hear each otherrA, C can not hear each other interfering at B6: Wireless and Mobile Networks6-13IEEE 802.11 Wireless LANr802.11bm2.4-5 GHz 无限制频段mup to 11 Mbpsm物理层采用直接序列扩频 (DSSS) all hosts use same chipping coder802.11a m5-6 GHz range

13、mup to 54 Mbpsr802.11g m2.4-5 GHz rangemup to 54 Mbpsr802.11n: 多天线m2.4-5 GHz rangemup to 200 Mbpsr都采用 CSMA/CA 进行多路访问r都有基站和自组网版本6: Wireless and Mobile Networks6-14802.11 LAN 体系结构r无线主机通过基站通信m基站 = 接入点 (AP)r基础设施模式中的基本服务集 (BSS) (aka “cell”) 包括:m无线主机m接入点 (AP): 基站m自组网(ad hoc)模式: 只包含主机BSS 1BSS 2Internethub,

14、 switchor routerAPAP6: Wireless and Mobile Networks6-15IEEE 802.11: 多路访问r碰撞避免: 2+ 节点同时传输r802.11: CSMA 传输前感知m不与其他节点正在进行的传输碰撞r802.11: 无冲突检测!m传送的同时难以接收(进行冲突检测)，因为微弱的接收信号 (衰减)m并非所有情况下都能感知到碰撞: 隐藏终端, 衰减m目标: 避免碰撞: CSMA/C(ollision)A(voidance)ABCABCAs signalstrengthspaceCs signalstrength6: Wireless and Mobil

15、e Networks6-16IEEE 802.11 MAC Protocol: CSMA/CA802.11 sender1 if sense channel idle for DIFS then transmit entire frame (no CD)2 if sense channel busy then start random backoff timetimer counts down while channel idletransmit when timer expiresif no ACK, increase random backoff interval, repeat 2802

16、.11 receiver- if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) senderreceiverDIFSdataSIFSACK6: Wireless and Mobile Networks6-17避免碰撞 (more)idea: 允许发送方“预约”信道而不是随机访问: 避免长数据帧的冲突r发送方首先使用CSMA 发送小的请求发送 (RTS)数据包到 BSmRTS包依然可能互相碰撞 (但是它们很短)rBS 广播可以发送 CTS 数据包响应 RTSr所有节点都能收到

17、RTSm发送者传送数据帧m其他节点推迟传输 使用小的预约包完全避免数据帧碰撞!6: Wireless and Mobile Networks6-18802.11: 高级功能能源管理rnode-to-AP: “将休眠直到下一信标帧到达”mAP 了解不再向该节点传输帧m节点在收到下一信标帧时唤醒r信标帧: 包含有AP-to-mobile帧需要发送移动节点的列表m若节点有AP-to-mobile 帧需要发送，则保持唤醒;否则将休眠直到下一信标帧到达6: Wireless and Mobile Networks6-19Mradius ofcoverageSSSPPPPMSMaster deviceSl

18、ave deviceParked device (inactive)P802.15: （个域网）personal area networkr直径 10 m 以内r取代电缆 (mouse, keyboard, headphones)rad hoc: 无基础设施r主/从设备:m从设备请求许可发送 (到主设备)m主设备许可请求r802.15: 由 Bluetooth 标准进化而来m2.4-2.5 GHz radio bandmup to 721 kbps6: Wireless and Mobile Networks6-20Mobile Switching CenterPublic telephone

19、network, andInternetMobile Switching Center蜂窝网络结构的组成q 将蜂窝连接到广域网q 管理呼叫建立 (more later!)q 处理移动性 (more later!)移动交换中心MSCq覆盖地理区域q类似 802.11 AP的基站(BS) q mobile users移动用户 通过BS接入网络q air-interface: 移动终端与 BS之间的物理层、链路层协议蜂窝cellwired network6: Wireless and Mobile Networks6-21蜂窝网络: 第一跳两类共享mobile-to-BS无线频段的技术r结合 FDM

20、A/TDMA: 将频段频分为信道，将信道时分为时隙rCDMA: 码分多路复用frequencybandstime slots6: Wireless and Mobile Networks6-22蜂窝网络标准: 简短的调查2G systems: 语音信道rIS-136 TDMA: combined FDMA/TDMA (north america)rGSM (global system for mobile communications): combined FDMA/TDMA mmost widely deployedrIS-95 CDMA: code division multiple ac

21、cessIS-136GSMIS-95GPRSEDGECDMA-2000UMTSTDMA/FDMADont drown in a bowlof alphabet soup: use thisfor reference only6: Wireless and Mobile Networks6-23蜂窝网络标准: 简短的调查2.5 G systems: 语音与数据信道rfor those who cant wait for 3G service: 2G extensionsrgeneral packet radio service (GPRS)mevolved from GSM mdata sent

22、 on multiple channels (if available)renhanced data rates for global evolution (EDGE)malso evolved from GSM, using enhanced modulation mdata rates up to 384KrCDMA-2000 (phase 1)mdata rates up to 144Kmevolved from IS-956: Wireless and Mobile Networks6-24蜂窝网络标准: 简短的调查3G systems: voice/datarUniversal Mo

23、bile Telecommunications Service (UMTS)mdata service: High Speed Uplink/Downlink packet Access (HSDPA/HSUPA): 3 MbpsrCDMA-2000: CDMA in TDMA slotsmdata service: 1xEvlution Data Optimized (1xEVDO) up to 14 Mbps . more (and more interesting) cellular topics due to mobility (stay tuned for details)6: Wi

24、reless and Mobile Networks6-25何为移动性?r移动性谱, 网络视角:no mobilityhigh mobilitymobile wireless user, using same access pointmobile user, passing through multiple access point while maintaining ongoing connections (like cell phone)mobile user, connecting/ disconnecting from network using DHCP. 6: Wireless a

25、nd Mobile Networks6-26移动性: 词汇表home network: permanent “home” of mobile(e.g., 128.119.40/24)Permanent address: address in home network, can always be used to reach mobilee.g., 86home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remotewide area net

26、workcorrespondent6: Wireless and Mobile Networks6-27移动性: 词汇表Care-of-address: address in visited network.(e.g., 79,129.13.2) wide area networkvisited network: network in which mobile currently resides (e.g., 79.129.13/24)Permanent address: remains constant (e.g., 86)foreign agent: entity

27、in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile6: Wireless and Mobile Networks6-28如何联系一个移动的友人:rsearch all phone books?rcall her parents?rexpect her to let you know where he/she is?I wonder where Alice moved to?Consider friend f

28、requently changing addresses, how do you find her?6: Wireless and Mobile Networks6-29移动性: 途径r由路由选择处理: 路由器通过通常的路由表交换公布其上常驻的移动节点的持久地址m路由表指示每个移动设备的位置m端系统无需变动r由端系统处理: m间接路由: 来自通信方的通信先到达home agent，然后再转发到远程网络m直接路由: 通信方获得移动用户的远端地址，直接向其发送数据6: Wireless and Mobile Networks6-30移动性: 途径rLet routing handle it: ro

29、uters advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.mrouting tables indicate where each mobile locatedmno changes to end-systemsrlet end-systems handle it: mindirect routing: communication from correspondent to mobile goes through home agent, then forwarde

30、d to remotemdirect routing: correspondent gets foreign address of mobile, sends directly to mobile对大量的终端，扩展性不足6: Wireless and Mobile Networks6-31Mobility: registrationEnd result:rForeign agent knows about mobilerHome agent knows location of mobilewide area networkhome networkvisited network1mobile c

31、ontacts foreign agent on entering visited network2foreign agent contacts home agent home: “this mobile is resident in my network”6: Wireless and Mobile Networks6-32Mobility via Indirect Routingwide area networkhomenetworkvisitednetwork3241correspondent addresses packets using home address of mobileh

32、ome agent intercepts packets, forwards to foreign agentforeign agent receives packets, forwards to mobilemobile replies directly to correspondent6: Wireless and Mobile Networks6-33Indirect Routing: commentsrMobile uses two addresses:mpermanent address: used by correspondent (hence mobile location is

33、 transparent to correspondent)mcare-of-address: used by home agent to forward datagrams to mobilerforeign agent functions may be done by mobile itselfrtriangle routing: correspondent-home-network-mobileminefficient when correspondent, mobile are in same network6: Wireless and Mobile Networks6-34Indi

34、rect Routing: moving between networksrsuppose mobile user moves to another networkmregisters with new foreign agentmnew foreign agent registers with home agentmhome agent update care-of-address for mobilempackets continue to be forwarded to mobile (but with new care-of-address)rmobility, changing foreign networks transparent: on going connections can be maintained!6: Wireless and Mobile Networks6-35Mobility via Direct Routingwide area networkhomenetworkvisitednetwork4