1、Chapter 6Wireless and Mobile NetworksComputer Networking: A Top Down Approach 6th edition Jim Kurose, Keith RossAddison-WesleyMarch 2012A 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 see the animat

2、ions; and can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lot of work on our part. In return for use, we only ask the following:vIf you use these slides (e.g., in a class) that you mention their source (after all, wed like peop

3、le to use our book!)vIf you post any slides 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/KWR All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights ReservedWireless, Mobile N

4、etworks6-1Wireless, Mobile Networks6-2Ch. 6: Wireless and Mobile NetworksBackground: v# wireless (mobile) phone subscribers now exceeds # wired phone subscribers (5-to-1)!v# wireless Internet-connected devices equals # wireline Internet-connected devices laptops, Internet-enabled phones promise anyt

5、ime untethered Internet accessvtwo important (but different) challengeswireless: communication over wireless linkmobility: handling the mobile user who changes point of attachment to networkWireless, Mobile Networks6-3Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristics CDMA

6、6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Access architecture standards (e.g., GSM)Mobility6.5 Principles: addressing and routing to mobile users6.6 Mobile IP6.7 Handling mobility in cellular networks6.8 Mobility and higher-layer protocols6.9 SummaryWireless, Mobile Networks6-4Ele

7、ments of a wireless networknetwork infrastructureWireless, Mobile Networks6-5wireless hostsvlaptop, smartphonevrun applicationsvmay be stationary (non-mobile) or mobile wireless does not always mean mobilityElements of a wireless networknetwork infrastructureWireless, Mobile Networks6-6 base station

8、vtypically connected to wired networkvrelay - responsible for sending packets between wired network and wireless host(s) in its “area” e.g., cell towers, 802.11 access points Elements of a wireless networknetwork infrastructureWireless, Mobile Networks6-7 wireless linkvtypically used to connect mobi

9、le(s) to base stationvalso used as backbone link vmultiple access protocol coordinates link access vvarious data rates, transmission distanceElements of a wireless networknetwork infrastructureWireless, Mobile Networks6-8Characteristics of selected wireless linksIndoor10-30mOutdoor50-200mMid-rangeou

10、tdoor200m 4 KmLong-rangeoutdoor5Km 20 Km.056.384145-11542G: IS-95, CDMA, GSM2.5G: UMTS/WCDMA, CDMA2000802.15802.11b802.11a,g3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO4G: LTWE WIMAX802.11a,g point-to-point200802.11nData rate (Mbps)Wireless, Mobile Networks6-9 infrastructure modevbase station connects mobi

11、les into wired networkvhandoff: mobile changes base station providing connection into wired networkElements of a wireless networknetwork infrastructureWireless, Mobile Networks 6-10ad hoc modevno base stationsvnodes can only transmit to other nodes within link coveragevnodes organize themselves into

12、 a network: route among themselvesElements of a wireless networkWireless, Mobile Networks 6-11Wireless network taxonomysingle hopmultiple hopsinfrastructure(e.g., APs)noinfrastructurehost connects to base station (WiFi,WiMAX, cellular) which connects to larger Internetno base station, noconnection t

13、o larger Internet (Bluetooth, ad hoc nets)host may have torelay through 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, VANETWireless, Mobile Networks 6-12Chapter 6 outline6.1 I

14、ntroduction Wireless6.2 Wireless links, characteristics CDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Access architecture standards (e.g., GSM)Mobility6.5 Principles: addressing and routing to mobile users6.6 Mobile IP6.7 Handling mobility in cellular networks6.8 Mobility and high

15、er-layer protocols6.9 SummaryWireless, Mobile Networks 6-13Wireless Link Characteristics (1)important differences from wired link .decreased signal strength: radio signal attenuates as it propagates through matter (path loss)interference from other sources: standardized wireless network frequencies

16、(e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as wellmultipath propagation: radio signal reflects off objects ground, arriving ad destination at slightly different times. make communication across (even a point to point) wireless link much more “difficult” Wireles

17、s, Mobile Networks 6-14Wireless Link Characteristics (2)vSNR: signal-to-noise ratio larger SNR easier to extract signal from noise (a “good thing”)vSNR versus BER tradeoffsgiven physical layer: increase power - increase SNR-decrease BERgiven SNR: choose physical layer that meets BER requirement, giv

18、ing highest thruput SNR may change with mobility: dynamically adapt physical layer (modulation technique, rate) 10203040QAM256 (8 Mbps)QAM16 (4 Mbps)BPSK (1 Mbps)SNR(dB)BER10-110-210-310-510-610-710-4Wireless, Mobile Networks 6-15Wireless network characteristicsMultiple wireless senders and receiver

19、s create additional problems (beyond multiple access):ABCHidden terminal problemvB, A hear each othervB, C hear each othervA, C can not hear each other means A, C unaware of their interference at BABCAs signalstrengthspaceCs signalstrengthSignal attenuation:vB, A hear each othervB, C hear each other

20、vA, C can not hear each other interfering at BWireless, Mobile Networks 6-16Code Division Multiple Access (CDMA)vunique “code” assigned to each user; i.e., code set partitioning all users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode data allows multiple user

21、s to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)vencoded signal = (original data) X (chipping sequence)vdecoding: inner-product of encoded signal and chipping sequenceWireless, Mobile Networks 6-17CDMA encode/decodeslot 1slot 0d1 = -11 1 111 -1 -1 -1 -

22、Zi,m= di.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 1channeloutputreceivercodereceive

23、dinputDi = S Zi,m.cmm=1MMWireless, Mobile Networks 6-18CDMA: two-sender interferenceusing same code as sender 1, receiver recovers sender 1s original data from summed channel data!Sender 1Sender 2channel sums together transmissions by sender 1 and 2Wireless, Mobile Networks 6-19Chapter 6 outline6.1

24、Introduction Wireless6.2 Wireless links, characteristics CDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Access architecture standards (e.g., GSM)Mobility6.5 Principles: addressing and routing to mobile users6.6 Mobile IP6.7 Handling mobility in cellular networks6.8 Mobility and hig

25、her-layer protocols6.9 SummaryWireless, Mobile Networks 6-20IEEE 802.11 Wireless LAN802.11bv2.4-5 GHz unlicensed spectrumvup to 11 Mbpsvdirect sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code802.11a 5-6 GHz range up to 54 Mbps802.11g 2.4-5 GHz range up to 54 Mbps802

26、.11n: multiple antennae 2.4-5 GHz range up to 200 Mbpsvall use CSMA/CA for multiple accessvall have base-station and ad-hoc network versionsWireless, Mobile Networks 6-21802.11 LAN architecturevwireless host communicates with base station base station = access point (AP)vBasic Service Set (BSS) (aka

27、 “cell”) in infrastructure mode contains: wireless hosts access point (AP): base station ad hoc mode: hosts onlyBSS 1BSS 2Internethub, switchor routerWireless, Mobile Networks 6-22802.11: Channels, associationv802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies AP adm

28、in chooses frequency for AP interference possible: channel can be same as that chosen by neighboring AP!vhost: must associate with an AP scans channels, listening for beacon frames containing APs name (SSID) and MAC address selects AP to associate with may perform authentication Chapter 8 will typic

29、ally run DHCP to get IP address in APs subnetWireless, Mobile Networks 6-23802.11: passive/active scanningAP 2AP 1H1BBS 2BBS 11231passive scanning: (1)beacon frames sent from APs(2)association Request frame sent: H1 to selected AP (3)association Response frame sent from selected AP to H1AP 2AP 1H1BB

30、S 2BBS 112234active scanning: (1) Probe Request frame broadcast from H1(2) Probe Response frames sent from APs(3) Association Request frame sent: H1 to selected AP (4) Association Response frame sent from selected AP to H1Wireless, Mobile Networks 6-24IEEE 802.11: multiple accessvavoid collisions: 2

31、+ nodes transmitting at same timev802.11: CSMA - sense before transmitting dont collide with ongoing transmission by other nodev802.11: no collision detection! difficult to receive (sense collisions) when transmitting due to weak received signals (fading) cant sense all collisions in any case: hidde

32、n terminal, fading goal: avoid collisions: CSMA/C(ollision)A(voidance)spaceABCABCAs signalstrengthCs signalstrengthWireless, Mobile Networks 6-25IEEE 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

33、backoff timetimer counts down while channel idletransmit when timer expiresif 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) senderreceiverDIFSdataSIFSACKWireless, Mobile Networks 6-26Avoiding

34、collisions (more)idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data framesvsender first transmits small request-to-send (RTS) packets to BS using CSMA RTSs may still collide with each other (but theyre short)vBS broadcasts clear-to-send CT

35、S in response to RTSvCTS heard by all nodes sender transmits data frame other stations defer transmissions avoid data frame collisions completely using small reservation packets!Wireless, Mobile Networks 6-27Collision Avoidance: RTS-CTS exchangeAPABtimeRTS(A)RTS(B)RTS(A)CTS(A)CTS(A)DATA (A)ACK(A)ACK

36、(A)reservation collisiondeferWireless, Mobile Networks 6-28framecontroldurationaddress1address2address4address3payloadCRC22666260 - 23124seqcontrol802.11 frame: addressingAddress 2: MAC addressof wireless host or AP transmitting this frameAddress 1: MAC addressof wireless host or AP to receive this

37、frameAddress 3: MAC addressof router interface to which AP is attachedAddress 4: used only in ad hoc modeWireless, Mobile Networks 6-29InternetrouterH1R1AP MAC addr H1 MAC addr R1 MAC addraddress 1address 2address 3802.11 frameR1 MAC addr H1 MAC addr dest. address source address 802.3 frame802.11 fr

38、ame: addressingWireless, Mobile Networks 6-30framecontroldurationaddress1address2address4address3payloadCRC22666260 - 23124seqcontrolTypeFromAPSubtypeToAPMore fragWEPMoredataPowermgtRetryRsvdProtocolversion22411111111duration of reserved transmission time (RTS/CTS)frame seq #(for RDT)frame type(RTS,

39、 CTS, ACK, data)802.11 frame: moreWireless, Mobile Networks 6-31802.11: mobility within same subnetvH1 remains in same IP subnet: IP address can remain samevswitch: which AP is associated with H1? self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to re

40、ach H1H1BBS 2BBS 1Wireless, Mobile Networks 6-32802.11: advanced capabilitiesRate adaptationvbase station, mobile dynamically change transmission rate (physical layer modulation technique) as mobile moves, SNR varies QAM256 (8 Mbps)QAM16 (4 Mbps)BPSK (1 Mbps)10203040SNR(dB)BER10-110-210-310-510-610-

41、710-4operating point1. SNR decreases, BER increase as node moves away from base station2. When BER becomes too high, switch to lower transmission rate but with lower BERWireless, Mobile Networks 6-33power managementvnode-to-AP: “I am going to sleep until next beacon frame” AP knows not to transmit f

42、rames to this node node wakes up before next beacon framevbeacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sent node will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next beacon frame802.11: advanced capabilitiesWireless, Mobile Networks 6-3

43、4Mradius ofcoverageSSSPPPPMSMaster deviceSlave deviceParked device (inactive)P802.15: personal area networkvless than 10 m diametervreplacement for cables (mouse, keyboard, headphones)vad hoc: no infrastructurevmaster/slaves: slaves request permission to send (to master) master grants requestsv802.1

44、5: evolved from Bluetooth specification 2.4-2.5 GHz radio band up to 721 kbpsWireless, Mobile Networks 6-35Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristics CDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet access architecture standards (e.g., GSM)Mobility6

45、.5 Principles: addressing and routing to mobile users6.6 Mobile IP6.7 Handling mobility in cellular networks6.8 Mobility and higher-layer protocols6.9 SummaryWireless, Mobile Networks 6-36Mobile Switching CenterPublic telephonenetworkMobile Switching CenterComponents of cellular network architecture

46、v connects cells to wired tel. net.v manages call setup (more later!)v handles mobility (more later!)MSCv covers geographical regionv base station (BS) analogous to 802.11 APv mobile users attach to network through BSv air-interface: physical and link layer protocol between mobile and BScellwired ne

47、tworkWireless, Mobile Networks 6-37Cellular networks: the first hopTwo techniques for sharing mobile-to-BS radio spectrumvcombined FDMA/TDMA: divide spectrum in frequency channels, divide each channel into time slotsvCDMA: code division multiple accessfrequencybandstime slotsWireless, Mobile Network

48、s 6-38BSCBTSBase transceiver station (BTS)Base station controller (BSC)Mobile Switching Center (MSC)Mobile subscribersBase station system (BSS)Legend2G (voice) network architecture MSCPublic telephonenetworkGatewayMSCGWireless, Mobile Networks 6-393G (voice+data) network architectureradionetwork con

49、trollerMSCSGSNPublic telephonenetworkGatewayMSCGServing GPRS Support Node (SGSN)Gateway GPRS Support Node (GGSN)Public InternetGGSNGKey insight: new cellular datanetwork operates in parallel (except at edge) with existing cellular voice networkv voice network unchanged in corev data network operates

50、 in parallelWireless, Mobile Networks 6-40radionetwork controllerMSCSGSNPublic telephonenetworkGatewayMSCGPublic InternetGGSNGradio access networkUniversal Terrestrial Radio Access Network (UTRAN)core networkGeneral Packet Radio Service (GPRS) Core NetworkpublicInternetradio interface(WCDMA, HSPA)3G

51、 (voice+data) network architectureWireless, Mobile Networks 6-41Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristics CDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Access architecture standards (e.g., GSM)Mobility6.5 Principles: addressing and routing to mo

52、bile users6.6 Mobile IP6.7 Handling mobility in cellular networks6.8 Mobility and higher-layer protocols6.9 SummaryWireless, Mobile Networks 6-42What is mobility?vspectrum of mobility, from the network perspective:no mobilityhigh mobilitymobile wireless user, using same access pointmobile user, pass

53、ing through multiple access point while maintaining ongoing connections (like cell phone)mobile user, connecting/ disconnecting from network using DHCP. wide area networkWireless, Mobile Networks 6-43Mobility: vocabularyhome network: permanent “home” of mobile(e.g., 128.119.40/24)permanent address:

54、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 remoteWireless, Mobile Networks 6-44Mobility: more vocabularywide area networkcare-of-address: address in visited network.(e.g.,

55、79,129.13.2) visited network: network in which mobile currently resides (e.g., 79.129.13/24)permanent address: remains constant (e.g., 86)foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobileWireless

56、, Mobile Networks 6-45How do you contact a mobile friend:vsearch all phone books?vcall her parents?vexpect 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?Wireless, Mobile Networks 6-46Mobility: approachesvlet routi

57、ng handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each mobile located no changes to end-systemsvlet end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent

58、, then forwarded to remotedirect routing: correspondent gets foreign address of mobile, sends directly to mobileWireless, Mobile Networks 6-47vlet routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. routing tables indicate where each

59、mobile located no changes to end-systemsvlet end-systems handle it: indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remotedirect routing: correspondent gets foreign address of mobile, sends directly to mobilenot scalable to millions of mobilesM

60、obility: approacheswide area networkWireless, Mobile Networks 6-48Mobility: registrationend result:vforeign agent knows about mobilevhome agent knows location of mobilehome networkvisited network1mobile contacts foreign agent on entering visited network2foreign agent contacts home agent home: “this