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: 無線與移動網絡背景: r無線電話使用者的數(shù)量已經超過了有線電話使用者的數(shù)量!r計算機網絡: 筆記本, 掌上型電腦, PDAs, 可以訪問Internet 的電話需要隨時可用的、無固定接入位置的 Inter

6、net 訪問r兩個重要的 (但不相同的) 挑戰(zhàn)m無線: 通過無線鏈路進行通信m移動性: 解決移動用戶改變連接到網絡的連接點的問題6: Wireless and Mobile Networks6-4無線網絡的構成要素network infrastructure無線主機rlaptop, PDA, IP phoner運行應用程序r可以是固定的或移動的m無線并不一定意味著移動性6: Wireless and Mobile Networks6-5無線網絡的構成要素network infrastructure 基站r通常與有線網絡連接r中繼 負責為處在其區(qū)域內的有線和無線主機間me.g., 蜂窩電話基站,

7、 802.11 接入點6: Wireless and Mobile Networks6-6無線網絡的構成要素network infrastructure 無線鏈路r通常用于連接移動終端和基站r也用作主干網連接r使用多路訪問協(xié)議協(xié)調鏈路訪問 r不同的傳輸速率和傳輸距離6: Wireless and Mobile Networks6-7部分無線鏈路標準的特性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無線網絡的構成要素network infrastructure基礎設施模式r基站將移動終端連接到有線網絡r切換: 移動終端改變接入有線網絡的基站6: Wireless and Mobile Networks6-9無線網絡的構成

9、要素自組網模式r不存在基站r節(jié)點間只能與連接范圍內進行傳輸r節(jié)點自組織網絡：在節(jié)點間自主安排路由6: Wireless and Mobile Networks6-10無線網絡分類單跳多跳有基礎設施(e.g., APs)無基礎設施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無線鏈路特性 (1)與有線鏈路的差異 .m信號強度衰減: 無線電信號隨著傳播距離的擴展變弱 (路徑損耗)m其他源的干擾: 標準無線網絡頻率 (e.g., 2.4 GHz)

11、是設備共享的 (e.g., phone); 設備間互相干擾m多徑傳播: 無線電信號在物體表面反射，到達目的地的存在輕微的時間差異. 通過無線鏈路進行通信 (哪怕只是一個節(jié)點到另一個節(jié)點)困難得多 6: Wireless and Mobile Networks6-12無線鏈路特性多個無線發(fā)送方和接收方帶來額外的問題 (不止是多路訪問):ABC隱藏終端問題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信號衰減: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 無限制頻段mup to 11 Mbpsm物理層采用直接序列擴頻 (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: 多天線m2.4-5 GHz rangemup to 200 Mbpsr都采用 CSMA/CA 進行多路訪問r都有基站和自組網版本6: Wireless and Mobile Networks6-14802.11 LAN 體系結構r無線主機通過基站通信m基站 = 接入點 (AP)r基礎設施模式中的基本服務集 (BSS) (aka “cell”) 包括:m無線主機m接入點 (AP): 基站m自組網(ad hoc)模式: 只包含主機BSS 1BSS 2Internethub,

14、 switchor routerAPAP6: Wireless and Mobile Networks6-15IEEE 802.11: 多路訪問r碰撞避免: 2+ 節(jié)點同時傳輸r802.11: CSMA 傳輸前感知m不與其他節(jié)點正在進行的傳輸碰撞r802.11: 無沖突檢測!m傳送的同時難以接收(進行沖突檢測)，因為微弱的接收信號 (衰減)m并非所有情況下都能感知到碰撞: 隱藏終端, 衰減m目標: 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: 允許發(fā)送方“預約”信道而不是隨機訪問: 避免長數(shù)據(jù)幀的沖突r發(fā)送方首先使用CSMA 發(fā)送小的請求發(fā)送 (RTS)數(shù)據(jù)包到 BSmRTS包依然可能互相碰撞 (但是它們很短)rBS 廣播可以發(fā)送 CTS 數(shù)據(jù)包響應 RTSr所有節(jié)點都能收到

17、RTSm發(fā)送者傳送數(shù)據(jù)幀m其他節(jié)點推遲傳輸 使用小的預約包完全避免數(shù)據(jù)幀碰撞!6: Wireless and Mobile Networks6-18802.11: 高級功能能源管理rnode-to-AP: “將休眠直到下一信標幀到達”mAP 了解不再向該節(jié)點傳輸幀m節(jié)點在收到下一信標幀時喚醒r信標幀: 包含有AP-to-mobile幀需要發(fā)送移動節(jié)點的列表m若節(jié)點有AP-to-mobile 幀需要發(fā)送，則保持喚醒;否則將休眠直到下一信標幀到達6: Wireless and Mobile Networks6-19Mradius ofcoverageSSSPPPPMSMaster deviceSl

18、ave deviceParked device (inactive)P802.15: （個域網）personal area networkr直徑 10 m 以內r取代電纜 (mouse, keyboard, headphones)rad hoc: 無基礎設施r主/從設備:m從設備請求許可發(fā)送 (到主設備)m主設備許可請求r802.15: 由 Bluetooth 標準進化而來m2.4-2.5 GHz radio bandmup to 721 kbps6: Wireless and Mobile Networks6-20Mobile Switching CenterPublic telephone

19、network, andInternetMobile Switching Center蜂窩網絡結構的組成q 將蜂窩連接到廣域網q 管理呼叫建立 (more later!)q 處理移動性 (more later!)移動交換中心MSCq覆蓋地理區(qū)域q類似 802.11 AP的基站(BS) q mobile users移動用戶 通過BS接入網絡q air-interface: 移動終端與 BS之間的物理層、鏈路層協(xié)議蜂窩cellwired network6: Wireless and Mobile Networks6-21蜂窩網絡: 第一跳兩類共享mobile-to-BS無線頻段的技術r結合 FDM

20、A/TDMA: 將頻段頻分為信道，將信道時分為時隙rCDMA: 碼分多路復用frequencybandstime slots6: Wireless and Mobile Networks6-22蜂窩網絡標準: 簡短的調查2G systems: 語音信道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蜂窩網絡標準: 簡短的調查2.5 G systems: 語音與數(shù)據(jù)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蜂窩網絡標準: 簡短的調查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何為移動性?r移動性譜, 網絡視角: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移動性: 詞匯表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移動性: 詞匯表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如何聯(lián)系一個移動的友人: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移動性: 途徑r由路由選擇處理: 路由器通過通常的路由表交換公布其上常駐的移動節(jié)點的持久地址m路由表指示每個移動設備的位置m端系統(tǒng)無需變動r由端系統(tǒng)處理: m間接路由: 來自通信方的通信先到達home agent，然后再轉發(fā)到遠程網絡m直接路由: 通信方獲得移動用戶的遠端地址，直接向其發(fā)送數(shù)據(jù)6: Wireless and Mobile Networks6-30移動性: 途徑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對大量的終端，擴展性不足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