【Chapter6】WirelessandMobileNetworks

1、6: Wireless and Mobile Networks6-1Chapter 6Wireless and Mobile NetworksComputer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith RossAddison-Wesley, July 2004. 6: Wireless and Mobile Networks6-2Chapter 6: Wireless and Mobile NetworksBackground: r# wireless (mobi

2、le) phone subscribers now exceeds # wired phone subscribers!rcomputer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet accessrtwo important (but different) challengesmcommunication over wireless linkmhandling mobile user who changes point of attachment to net

3、work6: Wireless and Mobile Networks6-3Chapter 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 Principles: addressing and routing to mobile usersr6.6 Mobile

4、IPr6.7 Handling mobility in cellular networksr6.8 Mobility and higher-layer protocols6.9 Summary6: Wireless and Mobile Networks6-4Elements of a wireless networknetwork infrastructurewireless hostsrlaptop, PDA, IP phonerrun applicationsrmay be stationary (non-mobile) or mobilemwireless does not alway

5、s mean mobility6: Wireless and Mobile Networks6-5Elements of a wireless networknetwork infrastructure base stationrtypically connected to wired networkrrelay - responsible for sending packets between wired network and wireless host(s) in its “area”me.g., cell towers 802.11 access points 6: Wireless

6、and Mobile Networks6-6Elements of a wireless networknetwork infrastructure wireless linkrtypically used to connect mobile(s) to base stationralso used as backbone link rmultiple access protocol coordinates link access rvarious data rates, transmission distance6: Wireless and Mobile Networks6-7Charac

7、teristics of selected wireless link standards384 Kbps56 Kbps54 Mbps5-11 Mbps1 Mbps802.15802.11b802.11a,gIS-95 CDMA, GSMUMTS/WCDMA, CDMA2000 .11 p-to-p link2G3GIndoor10 30mOutdoor50 200mMid rangeoutdoor200m 4KmLong rangeoutdoor5Km 20Km6: Wireless and Mobile Networks6-8Elements of a wireless networkne

8、twork infrastructure infrastructure moderbase station connects mobiles into wired networkrhandoff: mobile changes base station providing connection into wired network6: Wireless and Mobile Networks6-9Elements of a wireless networkAd hoc moderno base stationsrnodes can only transmit to other nodes wi

9、thin link coveragernodes organize themselves into a network: route among themselves6: Wireless and Mobile Networks6-10Wireless Link CharacteristicsDifferences from wired link .mdecreased signal strength: radio signal attenuates as it propagates through matter (path loss)minterference from other sour

10、ces: standardized wireless network frequencies (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as wellmmultipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times. make communication across (even a point to po

11、int) wireless link much more “difficult” 6: Wireless and Mobile Networks6-11Wireless network characteristicsMultiple wireless senders and receivers create additional problems (beyond multiple access):ABCHidden terminal problemrB, A hear each otherrB, C hear each otherrA, C can not hear each othermea

12、ns A, C unaware of their interference at BABCAs signalstrengthspaceCs signalstrengthSignal fading:rB, A hear each otherrB, C hear each otherrA, C can not hear each other interferring at B6: Wireless and Mobile Networks6-12Code Division Multiple Access (CDMA)rused in several wireless broadcast channe

13、ls (cellular, satellite, etc) standardsrunique “code” assigned to each user; i.e., code set partitioningrall users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode datarencoded signal = (original data) X (chipping sequence)rdecoding: inner-product of encoded sig

14、nal and chipping sequencerallows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)6: Wireless and Mobile Networks6-13CDMA Encode/Decodeslot 1slot 0d1 = -11 1 111 -1 -1 -1 -Zi,m= di.cmd0 = 11 1 111 -1 -1 -1 -1 1 111 -1 -1 -1 -1 1 111 -1 -1 -

15、1 -slot 0channeloutputslot 1channeloutputchannel output Zi,msendercodedatabitsslot 1slot 0d1 = -1d0 = 11 1 111 -1 -1 -1 -1 1 111 -1 -1 -1 -1 1 111 -1 -1 -1 -1 1 111 -1 -1 -1 -slot 0channeloutputslot 1channeloutputreceivercodereceivedinputDi = S Zi,m.cmm=1MM6: Wireless and Mobile Networks6-14CDMA: tw

16、o-sender interference6: Wireless and Mobile Networks6-15Chapter 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 Principles: addressing and routing to mobile

17、 usersr6.6 Mobile IPr6.7 Handling mobility in cellular networksr6.8 Mobility and higher-layer protocols6.9 Summary6: Wireless and Mobile Networks6-16IEEE 802.11 Wireless LANr802.11bm2.4-5 GHz unlicensed radio spectrummup to 11 Mbpsmdirect sequence spread spectrum (DSSS) in physical layer all hosts u

18、se same chipping codemwidely deployed, using base stationsr802.11a m5-6 GHz rangemup to 54 Mbpsr802.11g m2.4-5 GHz rangemup to 54 MbpsrAll use CSMA/CA for multiple accessrAll have base-station and ad-hoc network versions6: Wireless and Mobile Networks6-17802.11 LAN architecturerwireless host communi

19、cates with base stationmbase station = access point (AP)rBasic Service Set (BSS) (aka “cell”) in infrastructure mode contains:mwireless hostsmaccess point (AP): base stationmad hoc mode: hosts onlyBSS 1BSS 2Internethub, switchor routerAPAP6: Wireless and Mobile Networks6-18802.11: Channels, associat

20、ionr802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequenciesmAP admin chooses frequency for APminterference possible: channel can be same as that chosen by neighboring AP!rhost: must associate with an APmscans channels, listening for beacon frames containing APs name (SSID

21、) and MAC addressmselects AP to associate withmmay perform authentication Chapter 8mwill typically run DHCP to get IP address in APs subnet6: Wireless and Mobile Networks6-19IEEE 802.11: multiple accessravoid collisions: 2+ nodes transmitting at same timer802.11: CSMA - sense before transmittingmdon

22、t collide with ongoing transmission by other noder802.11: no collision detection!mdifficult to receive (sense collisions) when transmitting due to weak received signals (fading)mcant sense all collisions in any case: hidden terminal, fadingmgoal: avoid collisions: CSMA/C(ollision)A(voidance)ABCABCAs

23、 signalstrengthspaceCs signalstrength6: Wireless and Mobile Networks6-20IEEE 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 expir

24、esif no ACK, increase random backoff interval, repeat 2802.11 receiver- if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) senderreceiverDIFSdataSIFSACK6: Wireless and Mobile Networks6-21Avoiding collisions (more)idea: allow sender to “reserve” channel rather than

25、 random access of data frames: avoid collisions of long data framesrsender first transmits small request-to-send (RTS) packets to BS using CSMAmRTSs may still collide with each other (but theyre short)rBS broadcasts clear-to-send CTS in response to RTSrRTS heard by all nodesmsender transmits data fr

26、amemother stations defer transmissions Avoid data frame collisions completely using small reservation packets!6: Wireless and Mobile Networks6-22Collision Avoidance: RTS-CTS exchangeAPABtimeRTS(A)RTS(B)RTS(A)CTS(A)CTS(A)DATA (A)ACK(A)ACK(A)reservation collisiondefer6: Wireless and Mobile Networks6-2

27、3framecontroldurationaddress1address2address4address3payloadCRC22666260 - 23124seqcontrol802.11 frame: addressingAddress 2: MAC addressof wireless host or AP transmitting this frameAddress 1: MAC addressof wireless host or AP to receive this frameAddress 3: MAC addressof router interface to which AP

28、 is attachedAddress 3: used only in ad hoc mode6: Wireless and Mobile Networks6-24InternetrouterAPH1R1AP MAC addr H1 MAC addr R1 MAC addraddress 1address 2address 3802.11 frameR1 MAC addr AP MAC addr dest. address source address 802.3 frame802.11 frame: addressing6: Wireless and Mobile Networks6-25f

29、ramecontroldurationaddress1address2address4address3payloadCRC22666260 - 23124seqcontrolTypeFromAPSubtypeToAPMore fragWEPMoredataPowermgtRetryRsvdProtocolversion22411111111802.11 frame: moreduration of reserved transmission time (RTS/CTS)frame seq #(for reliable ARQ)frame type(RTS, CTS, ACK, data)6:

30、Wireless and Mobile Networks6-26hub or switchAP 2AP 1H1BBS 2BBS 1802.11: mobility within same subnetrouterrH1 remains in same IP subnet: IP address can remain samerswitch: which AP is associated with H1?mself-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be use

31、d to reach H16: Wireless and Mobile Networks6-27Mradius ofcoverageSSSPPPPMSMaster deviceSlave deviceParked device (inactive)P802.15: personal area networkrless than 10 m diameterrreplacement for cables (mouse, keyboard, headphones)rad hoc: no infrastructurermaster/slaves:mslaves request permission t

32、o send (to master)mmaster grants requestsr802.15: evolved from Bluetooth specificationm2.4-2.5 GHz radio bandmup to 721 kbps6: Wireless and Mobile Networks6-28Chapter 6 outline6.1 Introduction Wirelessr6.2 Wireless links, characteristicsmCDMAr6.3 IEEE 802.11 wireless LANs (“wi-fi”)r6.4 Cellular Inte

33、rnet Accessmarchitecturemstandards (e.g., GSM)Mobilityr6.5 Principles: 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 Networks6-29Mobile Switching CenterPublic telephonenetwork,

34、andInternetMobile Switching CenterComponents of cellular network architectureq connects cells to wide area netq manages call setup (more later!)q handles mobility (more later!)MSCq covers geographical regionq base station (BS) analogous to 802.11 APq mobile users attach to network through BSq air-in

35、terface: physical and link layer protocol between mobile and BScellwired network6: Wireless and Mobile Networks6-30Cellular networks: the first hopTwo techniques for sharing mobile-to-BS radio spectrumrcombined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slotsrCDM

36、A: code division multiple accessfrequencybandstime slots6: Wireless and Mobile Networks6-31Cellular standards: brief survey2G systems: voice channelsrIS-136 TDMA: combined FDMA/TDMA (north america)rGSM (global system for mobile communications): combined FDMA/TDMA mmost widely deployedrIS-95 CDMA: co

37、de division multiple accessIS-136GSMIS-95GPRSEDGECDMA-2000UMTSTDMA/FDMADont drown in a bowlof alphabet soup: use thisoor reference only6: Wireless and Mobile Networks6-32Cellular standards: brief survey2.5 G systems: voice and data channelsrfor those who cant wait for 3G service: 2G extensionsrgener

38、al packet radio service (GPRS)mevolved from GSM mdata sent on multiple channels (if available)renhanced data rates for global evolution (EDGE)malso evolved from GSM, using enhanced modulation mDate rates up to 384KrCDMA-2000 (phase 1)mdata rates up to 144Kmevolved from IS-956: Wireless and Mobile Ne

39、tworks6-33Cellular standards: brief survey3G systems: voice/datarUniversal Mobile Telecommunications Service (UMTS)mGSM next step, but using CDMArCDMA-2000 . more (and more interesting) cellular topics due to mobility (stay tuned for details)6: Wireless and Mobile Networks6-34Chapter 6 outline6.1 In

40、troduction Wirelessr6.2 Wireless links, characteristicsmCDMAr6.3 IEEE 802.11 wireless LANs (“wi-fi”)r6.4 Cellular Internet Accessmarchitecturemstandards (e.g., GSM)Mobilityr6.5 Principles: addressing and routing to mobile usersr6.6 Mobile IPr6.7 Handling mobility in cellular networksr6.8 Mobility an

41、d higher-layer protocols6.9 Summary6: Wireless and Mobile Networks6-35What is mobility?rspectrum of mobility, from the network perspective:no mobilityhigh mobilitymobile wireless user, using same access pointmobile user, passing through multiple access point while maintaining ongoing connections (li

42、ke cell phone)mobile user, connecting/ disconnecting from network using DHCP. 6: Wireless and Mobile Networks6-36Mobility: Vocabularyhome 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., 128.119.40.186home age

43、nt: entity that will perform mobility functions on behalf of mobile, when mobile is remotewide area networkcorrespondent6: Wireless and Mobile Networks6-37Mobility: more vocabularyCare-of-address: address in visited network.(e.g., 79,129.13.2) wide area networkvisited network: network in which mobil

44、e currently resides (e.g., 79.129.13/24)Permanent address: remains constant (e.g., 128.119.40.186)home agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile6: Wireless and Mobile Networks6-38How do you contact a mobile

45、friend: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 frequently changing addresses, how do you find her?6: Wireless and Mobile Networks6-39Mobility: approachesrLet routing handle it: routers advertise permanent add

46、ress 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 forwarded to remotemdirect routing: c

47、orrespondent gets foreign address of mobile, sends directly to mobile6: Wireless and Mobile Networks6-40Mobility: approachesrLet routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.mrouting tables indicate where each mobile locatedmno

48、changes to end-systemsrlet end-systems handle it: mindirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remotemdirect routing: correspondent gets foreign address of mobile, sends directly to mobilenot scalable to millions of mobiles6: Wireless and M

49、obile Networks6-41Mobility: registrationEnd result:rForeign agent knows about mobilerHome agent knows location of mobilewide area networkhome networkvisited network1mobile contacts foreign agent on entering visited network2foreign agent contacts home agent home: “this mobile is resident in my networ

50、k”6: Wireless and Mobile Networks6-42Mobility via Indirect Routingwide area networkhomenetworkvisitednetwork3241correspondent addresses packets using home address of mobilehome agent intercepts packets, forwards to foreign agentforeign agent receives packets, forwards to mobilemobile replies directl

51、y to correspondent6: Wireless and Mobile Networks6-43Indirect Routing: commentsrMobile uses two addresses:mpermanent address: used by correspondent (hence mobile location is transparent to correspondent)mcare-of-address: used by home agent to forward datagrams to mobilerforeign agent functions may b

52、e done by mobile itselfrtriangle routing: correspondent-home-network-mobileminefficient when correspondent, mobile are in same network6: Wireless and Mobile Networks6-44Indirect Routing: moving between networksrsuppose mobile user moves to another networkmregisters with new foreign agentmnew foreign

53、 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 Networks6-45Mobility via Direct Routi

54、ngwide area networkhomenetworkvisitednetwork4241correspondent requests, receives foreign address of mobilecorrespondent forwards to foreign agentforeign agent receives packets, forwards to mobilemobile replies directly to correspondent36: Wireless and Mobile Networks6-46Mobility via Direct Routing:

55、commentsrovercome triangle routing problemrnon-transparent to correspondent: correspondent must get care-of-address from home agentmwhat if mobile changes visited network?6: Wireless and Mobile Networks6-47wide area network1foreign net visited at session startanchorforeignagent24new foreignagent35co

56、rrespondentagentcorrespondentnew foreignnetworkAccommodating mobility with direct routingranchor foreign agent: FA in first visited networkrdata always routed first to anchor FArwhen mobile moves: new FA arranges to have data forwarded from old FA (chaining)6: Wireless and Mobile Networks6-48Chapter

57、 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 Principles: addressing and routing to mobile usersr6.6 Mobile IPr6.7 Handling mobility in cellular networks

58、r6.8 Mobility and higher-layer protocols6.9 Summary6: Wireless and Mobile Networks6-49Mobile IPrRFC 3220rhas many features weve seen: mhome agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)rthree components to standard:mindirect routing of

59、datagramsmagent discoverymregistration with home agent6: Wireless and Mobile Networks6-50Mobile IP: indirect routingPermanent address: 128.119.40.186Care-of address: 79.129.13.2dest: 128.119.40.186packet sent by correspondentdest: 79.129.13.2dest: 128.119.40.186packet sent by home agent to foreign a

60、gent: a packet within a packetdest: 128.119.40.186foreign-agent-to-mobile packet6: Wireless and Mobile Networks6-51Mobile IP: agent discoveryragent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) RBHFMGV bits reserved type = 16 type = 9 code = 0 = 9