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1、Chapter 6Wireless and Mobile NetworksComputer Networking:A Top Down Approach Featuring the Internet,3rd edition.Jim Kurose,Keith RossAddison-Wesley,July 2004.16:Wireless and Mobile NetworksChapter 6:Wireless and Mobile NetworksBackground:r#wireless(mobile)phone subscribers now exceeds#wired phone su
2、bscribers!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 network26:Wireless and Mobile NetworksChapter 6 outline6.1
3、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 networksr6.8 Mobility and h
4、igher-layer protocols6.9 Summary36:Wireless and Mobile NetworksElements of a wireless networknetwork infrastructurewireless hostsrlaptop,PDA,IP phonerrun applicationsrmay be stationary(non-mobile)or mobilemwireless does not always mean mobility46:Wireless and Mobile NetworksElements of a wireless ne
5、tworknetwork 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 56:Wireless and Mobile NetworksElements of a wireless networknetwork infrastructure wireles
6、s linkrtypically used to connect mobile(s)to base stationralso used as backbone link rmultiple access protocol coordinates link access rvarious data rates,transmission distance66:Wireless and Mobile NetworksCharacteristics of selected wireless link standards384 Kbps56 Kbps54 Mbps5-11 Mbps1 Mbps2G3GI
7、ndoor10 30mOutdoor50 200mMid rangeoutdoor200m 4KmLong rangeoutdoor5Km 20Km76:Wireless and Mobile NetworksElements of a wireless networknetwork infrastructure infrastructure moderbase station connects mobiles into wired networkrhandoff:mobile changes base station providing connection into wired netwo
8、rk86:Wireless and Mobile NetworksElements of a wireless networkAd hoc moderno base stationsrnodes can only transmit to other nodes within link coveragernodes organize themselves into a network:route among themselves96:Wireless and Mobile NetworksWireless Link CharacteristicsDifferences from wired li
9、nk.mdecreased signal strength:radio signal attenuates as it propagates through matter(path loss)minterference from other sources: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
10、 objects ground,arriving ad destination at slightly different times.make communication across(even a point to point)wireless link much more“difficult”106:Wireless and Mobile NetworksWireless network characteristicsMultiple wireless senders and receivers create additional problems(beyond multiple acc
11、ess):ABCHidden terminal problemrB,A hear each otherrB,C hear each otherrA,C can not hear each othermeans 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 B116:Wireless an
12、d Mobile NetworksCode Division Multiple Access(CDMA)rused in several wireless broadcast channels(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 signa
13、l=(original data)X(chipping sequence)rdecoding:inner-product of encoded signal and chipping sequencerallows multiple users to“coexist”and transmit simultaneously with minimal interference(if codes are“orthogonal”)126:Wireless and Mobile NetworksCDMA Encode/Decodeslot 1slot 0d1=-11 1 111-1-1-1-Zi,m=d
14、i.cmd0=11 1 111-1-1-1-1 1 111-1-1-1-1 1 111-1-1-1-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=1MM136:Wireless and M
15、obile NetworksCDMA:two-sender interference146:Wireless and Mobile NetworksChapter 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 rout
16、ing to mobile usersr6.6 Mobile IPr6.7 Handling mobility in cellular networksr6.8 Mobility and higher-layer protocols6.9 Summary156:Wireless and Mobile NetworksIEEE 802.11 Wireless LANr802.11bm2.4-5 GHz unlicensed radio spectrummup to 11 Mbpsmdirect sequence spread spectrum(DSSS)in physical layerall
17、hosts use 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 versions166:Wireless and Mobile Networks802.11 LAN architecturerwireless host comm
18、unicates 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 routerAPAP176:Wireless and Mobile Networks802.11:Channels,associationr802.11b:2
19、.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)and MAC addressms
20、elects AP to associate withmmay perform authentication Chapter 8mwill typically run DHCP to get IP address in APs subnet186:Wireless and Mobile NetworksIEEE 802.11:multiple accessravoid collisions:2+nodes transmitting at same timer802.11:CSMA-sense before transmittingmdont collide with ongoing trans
21、mission 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 signalstrengthspaceCs signalstrengt
22、h196:Wireless and Mobile NetworksIEEE 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 inter
23、val,repeat 2802.11 receiver-if frame received OK return ACK after SIFS(ACK needed due to hidden terminal problem)senderreceiverDIFSdataSIFSACK206:Wireless and Mobile NetworksAvoiding collisions(more)idea:allow sender to“reserve”channel rather than random access of data frames:avoid collisions of lon
24、g 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 framemother stations defer transmissions Avoid data frame c
25、ollisions completely using small reservation packets!216:Wireless and Mobile NetworksCollision Avoidance:RTS-CTS exchangeAPABtimeRTS(A)RTS(B)RTS(A)CTS(A)CTS(A)DATA(A)ACK(A)ACK(A)reservation collisiondefer226:Wireless and Mobile Networksframecontroldurationaddress1address2address4address3payloadCRC22
26、666260-23124seqcontrol802.11 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 is attachedAddress 4:used only in ad hoc mode236:Wireless and Mobile N
27、etworksInternetrouterAPH1R1AP 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:addressing246:Wireless and Mobile Networksframecontroldurationaddress1address2address4address3payloadCRC22666260-23124seqco
28、ntrolTypeFromAPSubtypeToAPMore fragWEPMoredataPowermgtRetryRsvdProtocolversion22411111111802.11 frame:moreduration of reserved transmission time(RTS/CTS)frame seq#(for reliable ARQ)frame type(RTS,CTS,ACK,data)256:Wireless and Mobile Networkshub or switchAP 2AP 1H1BBS 2BBS 1802.11:mobility within sam
29、e 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 used to reach H1266:Wireless and Mobile NetworksMradius ofcoverageSSSPPPPMSMaster deviceSlave devicePa
30、rked device(inactive)P802.15:personal area networkrless than 10 m diameterrreplacement for cables(mouse,keyboard,headphones)rad hoc:no infrastructurermaster/slaves:mslaves request permission to send(to master)mmaster grants requestsr802.15:evolved from Bluetooth specificationm2.4-2.5 GHz radio bandm
31、up to 721 kbps276:Wireless and Mobile NetworksChapter 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 Mobi
32、le IPr6.7 Handling mobility in cellular networksr6.8 Mobility and higher-layer protocols6.9 Summary286:Wireless and Mobile NetworksMobile Switching CenterPublic telephonenetwork,andInternetMobile Switching CenterComponents of cellular network architectureq connects cells to wide area netq manages ca
33、ll 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-interface:physical and link layer protocol between mobile and BScellwired network296:Wireless and Mobile NetworksCellular networ
34、ks:the first hopTwo techniques for sharing mobile-to-BS radio spectrumrcombined FDMA/TDMA:divide spectrum in frequency channels,divide each channel into time slotsrCDMA:code division multiple accessfrequencybandstime slots306:Wireless and Mobile NetworksCellular standards:brief survey2G systems:voic
35、e channelsrIS-136 TDMA:combined FDMA/TDMA(north america)rGSM(global system for mobile communications):combined FDMA/TDMA mmost widely deployedrIS-95 CDMA:code division multiple accessIS-136GSMIS-95GPRSEDGECDMA-2000UMTSTDMA/FDMADont drown in a bowlof alphabet soup:use thisoor reference only316:Wirele
36、ss and Mobile NetworksCellular standards:brief survey2.5 G systems:voice and data channelsrfor those who cant wait for 3G service:2G extensionsrgeneral packet radio service(GPRS)mevolved from GSM mdata sent on multiple channels(if available)renhanced data rates for global evolution(EDGE)malso evolve
37、d from GSM,using enhanced modulation mDate rates up to 384KrCDMA-2000(phase 1)mdata rates up to 144Kmevolved from IS-95326:Wireless and Mobile NetworksCellular standards:brief survey3G systems:voice/datarUniversal Mobile Telecommunications Service(UMTS)mGSM next step,but using CDMArCDMA-2000 TDS-CDM
38、A .more(and more interesting)cellular topics due to mobility(stay tuned for details)336:Wireless and Mobile NetworksChapter 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)M
39、obilityr6.5 Principles:addressing and routing to mobile usersr6.6 Mobile IPr6.7 Handling mobility in cellular networksr6.8 Mobility and higher-layer protocols6.9 Summary346:Wireless and Mobile NetworksWhat is mobility?rspectrum of mobility,from the network perspective:no mobilityhigh mobilitymobile
40、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.356:Wireless and Mobile NetworksMobility:Vocabularyhome network:permanent“home”of mobile(e.g.,128.
41、119.40/24)Permanent address:address in home network,can always be used to reach mobilee.g.,128.119.40.186home agent:entity that will perform mobility functions on behalf of mobile,when mobile is remotewide area networkcorrespondent366:Wireless and Mobile NetworksMobility:more vocabularyCare-of-addre
42、ss: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.,128.119.40.186)foreign agent:entity in visited network that performs mobility functions on behalf of mobile.corresponde
43、nt:wants to communicate with mobile376:Wireless and Mobile NetworksHow do you contact a mobile 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?386:Wireless and
44、 Mobile NetworksMobility: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 changes to end-systemsrLet end-systems handle it:mindirect routing:communication from corr
45、espondent to mobile goes through home agent,then forwarded to remotemdirect routing:correspondent gets foreign address of mobile,sends directly to mobile396:Wireless and Mobile NetworksMobility:approachesrLet routing handle it:routers advertise permanent address of mobile-nodes-in-residence via usua
46、l 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:correspondent gets foreign address of mobile,se
47、nds directly to mobilenot scalable to millions of mobiles406:Wireless and Mobile NetworksMobility:registrationEnd result:rForeign agent knows about mobilerHome agent knows location of mobilewide area networkhome networkvisited network1mobile contacts foreign agent on entering visited network2foreign
48、 agent contacts home agent home:“this mobile is resident in my network”416:Wireless and Mobile NetworksMobility via Indirect Routingwide area networkhomenetworkvisitednetwork3241correspondent addresses packets using home address of mobilehome agent intercepts packets,forwards to foreign agentforeign
49、 agent receives packets,forwards to mobilemobile replies directly to correspondent426:Wireless and Mobile NetworksIndirect 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
50、forward datagrams to mobilerforeign agent functions may be done by mobile itselfrtriangle routing:correspondent-home-network-mobileminefficient when correspondent,mobile are in same network436:Wireless and Mobile NetworksIndirect Routing:moving between networksrsuppose mobile user moves to another n