Computer Networking Wireless and Mobile Networking

6: Wireless and Mobile Networks6-1Chapter 6Wireless and Mobile NetworksA note on the use of these ppt slides:We’re making these slides freely available to all (faculty, students, readers). They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. They obviously represent a lotof work on our part. In return for use, we only ask the following:If you use these slides (e.g., in a class) in substantially unaltered form, that you mention their source (after all, we’d like people to use our book!)If you post any slides in substantially 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 4thedition. Jim Kurose, Keith RossAddison-Wesley, July 2007. 6: Wireless and Mobile Networks6-2Chapter 6: Wireless and Mobile NetworksBackground:# wireless (mobile) phone subscribers now exceeds # wired phone subscribers!computer nets: laptops, palmtops, PDAs, Internet-enabled phone promise anytime untethered Internet accesstwo important (but different) challengeswireless:communication over wireless linkmobility:handling the mobile user who changes point of attachment to network6: Wireless and Mobile Networks6-3Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“wi-fi”)6.4Cellular Internet Accessarchitecturestandards (e.g., GSM)Mobility6.5Principles: addressing and routing to mobile users6.6Mobile IP6.7Handling mobility in cellular networks6.8Mobility and higher-layer protocols6.9Summary6: Wireless and Mobile Networks6-4Elements of a wireless networknetwork infrastructurewireless hostslaptop, PDA, IP phonerun applicationsmay be stationary (non-mobile) or mobilewireless does notalways mean mobility6: Wireless and Mobile Networks6-5Elements of a wireless networknetwork infrastructurebase stationtypically connected to wired networkrelay -responsible for sending packets between wired network and wireless host(s) in its “area”e.g., cell towers, 802.11 access points 6: Wireless and Mobile Networks6-6Elements of a wireless networknetwork infrastructurewireless linktypically used to connect mobile(s) to base stationalso used as backbone link multiple access protocol coordinates link access various data rates, transmission distance6: Wireless and Mobile Networks6-7Characteristics of selected wireless link standardsIndoor10-30mOutdoor50-200mMid-rangeoutdoor200m –4 KmLong-rangeoutdoor5Km –20 Km.056.384145-1154IS-95, CDMA, GSM2GUMTS/WCDMA, 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 Networks6-8Elements of a wireless networknetwork infrastructureinfrastructure modebase station connects mobiles into wired networkhandoff: mobile changes base station providing connection into wired network6: Wireless and Mobile Networks6-9Elements of a wireless networkad hoc modeno base stationsnodes can only transmit to other nodes within link coveragenodes organize themselves into a network: route among themselves6: Wireless and Mobile Networks6-10Wireless network taxonomysingle hopmultiple hopsinfrastructure(e.g., APs)noinfrastructurehost 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 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, VANET6: Wireless and Mobile Networks6-11Wireless Link Characteristics (1)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 (e.g., 2.4 GHz) shared by other devices (e.g., phone); devices (motors) interfere as wellmultipath 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” 6: Wireless and Mobile Networks6-12Wireless Link Characteristics (2)SNR: signal-to-noise ratiolarger SNR –easier to extract signal from noise (a “good thing”)SNR versus BER tradeoffsgiven physical layer:increase power -> increase SNR->decrease BERgiven SNR:choose physical layer that meets BER requirement, giving 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)BER10-110-210-310-510-610-710-46: Wireless and Mobile Networks6-13Wireless network characteristicsMultiple wireless senders and receivers create additional problems (beyond multiple access):ABCHidden terminal problemB, A hear each otherB, C hear each otherA, C can not hear each othermeans A, C unaware of their interference at BABCA’s signalstrengthspaceC’s signalstrengthSignal attenuation:B, A hear each otherB, C hear each otherA, C can not hear each other interfering at B6: Wireless and Mobile Networks6-14Code Division Multiple Access (CDMA)used in several wireless broadcast channels (cellular, satellite, etc) standardsunique “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encoded signal= (original data) X (chipping sequence)decoding:inner-product of encoded signal and chipping sequenceallows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)6: Wireless and Mobile Networks6-15CDMA Encode/Decodeslot 1slot 0d1= -111111-1-1-1-Zi,m= di.cmd0= 111111-1-1-1-11111-1-1-1-11111-1-1-1-slot 0channeloutputslot 1channeloutputchannel output Zi,msendercodedatabitsslot 1slot 0d1= -1d0= 111111-1-1-1-11111-1-1-1-11111-1-1-1-11111-1-1-1-slot 0channeloutputslot 1channeloutputreceivercodereceivedinputDi = SZi,m.cmm=1MM6: Wireless and Mobile Networks6-16CDMA: two-sender interference6: Wireless and Mobile Networks6-17Chapter 6 outline6.1IntroductionWireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“wi-fi”)6.4cellular Internet accessarchitecturestandards (e.g., GSM)Mobility6.5Principles: addressing and routing to mobile users6.6Mobile IP6.7Handling mobility in cellular networks6.8Mobility and higher-layer protocols6.9Summary6: Wireless and Mobile Networks6-18IEEE 802.11 Wireless LAN802.11b2.4-5 GHz unlicensed spectrumup to 11 Mbpsdirect sequence spread spectrum (DSSS) in physical layer•all hosts use same chipping code802.11a5-6 GHz rangeup to 54 Mbps802.11g2.4-5 GHz rangeup to 54 Mbps802.11n: multiple antennae2.4-5 GHz rangeup to 200 Mbpsall use CSMA/CA for multiple accessall have base-station and ad-hoc network versions6: Wireless and Mobile Networks6-19802.11 LAN architecturewireless host communicates with base stationbase station = access point (AP)Basic Service Set (BSS)(aka “cell”) in infrastructure mode contains:wireless hostsaccess point (AP): base stationad hoc mode: hosts onlyBSS 1BSS 2Internethub, switchor routerAPAP6: Wireless and Mobile Networks6-20802.11: Channels, association802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequenciesAP admin chooses frequency for APinterference possible: channel can be same as that chosen by neighboring AP!host: must associatewith an APscans channels, listening for beacon framescontaining AP’s name (SSID) and MAC addressselects AP to associate withmay perform authentication [Chapter 8]will typically run DHCP to get IP address in AP’s subnet6: Wireless and Mobile Networks6-21802.11: passive/active scanningAP 2AP 1H1BBS 2BBS 112234Active Scanning: (1)Probe Request frame broadcast from H1(2)Probes response frame sent from APs(3)Association Request frame sent: H1 to selected AP (4)Association Response frame sent: H1 to selected APAP 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: H1 to selected AP6: Wireless and Mobile Networks6-22IEEE 802.11: multiple accessavoid collisions: 2+nodes transmitting at same time802.11: CSMA -sense before transmittingdon’t collide with ongoing transmission by other node802.11: nocollision detection!difficult to receive (sense collisions) when transmitting due to weak received signals (fading)can’t sense all collisions in any case: hidden terminal, fadinggoal: avoid collisions:CSMA/C(ollision)A(voidance)ABCABCA’s signalstrengthspaceC’s signalstrength6: Wireless and Mobile Networks6-23IEEE 802.11 MAC Protocol: CSMA/CA802.11 sender1 if sense channel idlefor DIFSthentransmit entire frame (no CD)2 ifsense channel busy thenstart random backoff timetimer counts down while channel idletransmit when timer expiresif no ACK, increase random backoff interval, repeat 2802.11 receiver-if frame received OKreturn ACK after SIFS (ACK needed due to hidden terminal problem) senderreceiverDIFSdataSIFSACK6: Wireless and Mobile Networks6-24Avoiding collisions (more)idea:allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data framessender first transmits smallrequest-to-send (RTS) packets to BS using CSMARTSs may still collide with each other (but they’re short)BS broadcasts clear-to-send CTS in response to RTSRTS heard by all nodessender transmits data frameother stations defer transmissions avoid data frame collisions completely using small reservation packets!6: Wireless and Mobile Networks6-25Collision Avoidance: RTS-CTS exchangeAPABtimeRTS(A)RTS(B)CTS(DATA (A)ACK(reservation collisiondefer6: Wireless and Mobile Networks6-26framecontroldurationaddress1address2address4address3payloadCRC22666260 -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 mode6: Wireless and Mobile Networks6-27InternetrouterAPH1R1AP MAC addr H1 MAC addr R1 MAC addraddress 1address 2address 3802.11frameR1 MAC addr AP MAC addr dest. address source address 802.3frame802.11 frame: addressing6: Wireless and Mobile Networks6-28framecontroldurationaddress1address2address4address3payloadCRC22666260 -23124seqcontrolTypeFromAPSubtypeToAPMore fragWEPMoredataPowermgtRetryRsvdProtocolversion22411111111802.11 frame: moreduration of reserved transmission time (RTS/CTS)frame seq #(for reliable ARQ)frame type(RTS, CTS, ACK, data)6: Wireless and Mobile Networks6-29hub or switchAP 2AP 1H1BBS 2BBS 1802.11: mobility within same subnetrouterH1 remains in same IP subnet: IP address can remain sameswitch: 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 reach H16: Wireless and Mobile Networks6-30802.11: advanced capabilitiesRate Adaptationbase 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)BER10-110-210-310-510-610-710-4operating 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 BER6: Wireless and Mobile Networks6-31802.11: advanced capabilitiesPower Managementnode-to-AP: “I am going to sleep until next beacon frame”AP knows not to transmit frames to this nodenode wakes up before next beacon framebeacon 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 frame6: Wireless and Mobile Networks6-32Mradius ofcoverageSSSPPPPMSMaster deviceSlave deviceParked device (inactive)P802.15: personal area networkless than 10 m diameterreplacement for cables (mouse, keyboard, headphones)ad hoc: no infrastructuremaster/slaves:slaves request permission to send (to master)master grants requests802.15: evolved from Bluetooth specification2.4-2.5 GHz radio bandup to 721 kbps6: Wireless and Mobile Networks6-33802.16: WiMAXlike 802.11 & cellular: base station modeltransmissions to/from base station by hosts with omnidirectional antennabase station-to-base station backhaul with point-to-point antennaunlike 802.11:range ~ 6 miles (“city rather than coffee shop”)~14 Mbpspoint-to-multipointpoint-to-point6: Wireless and Mobile Networks6-34802.16: WiMAX: downlink, uplink schedulingtransmission framedown-link subframe: base station to node uplink subframe: node to base stationpream.DL-MAPUL-MAPDLburst 1SS #1DLburst 2DLburst nInitialmaint.requestconn.downlink subframeSS #2SS #kuplink subframe…………base station tells nodes who will get to receive (DL map) and who will get to send (UL map), and whenWiMAX standard provide mechanism for scheduling, but not scheduling algorithm6: Wireless and Mobile Networks6-35Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“wi-fi”)6.4 Cellular Internet Accessarchitecturestandards (e.g., GSM)Mobility6.5Principles: addressing and routing to mobile users6.6Mobile IP6.7Handling mobility in cellular networks6.8Mobility and higher-layer protocols6.9Summary6: Wireless and Mobile Networks6-36Mobile Switching CenterPublic telephonenetwork, andInternetMobile Switching CenterComponents of cellular network architectureconnects cells to wide area netmanages call setup (more later!)handles mobility (more later!)MSCcovers geographical regionbase station(BS) analogous to 802.11 APmobile usersattach to network through BSair-interface:physical and link layer protocol between mobile and BScellwired network6: Wireless and Mobile Networks6-37Cellular networks: the first hopTwo techniques for sharing mobile-to-BS radio spectrumcombined FDMA/TDMA:divide spectrum in frequency channels, divide each channel into time slotsCDMA:code division multiple accessfrequencybandstime slots6: Wireless and Mobile Networks6-38Cellular standards: brief survey2G systems:voice channelsIS-136 TDMA: combined FDMA/TDMA (north america)GSM (global system for mobile communications): combined FDMA/TDMA most widely deployedIS-95 CDMA: code division multiple accessIS-136GSMIS-95GPRSEDGECDMA-2000UMTSTDMA/FDMADon’t drown in a bowlof alphabet soup: use thisfor reference only6: Wireless and Mobile Networks6-39Cellular standards: brief survey2.5 G systems:voice and data channelsfor those who can’t wait for 3G service: 2G extensionsgeneral packet radio service(GPRS)evolved from GSM data sent on multiple channels (if available)enhanced data rates for global evolution (EDGE)also evolved from GSM, using enhanced modulation data rates up to 384KCDMA-2000(phase 1)data rates up to 144Kevolved from IS-956: Wireless and Mobile Networks6-40Cellular standards: brief survey3G systems:voice/dataUniversal Mobile Telecommunications Service (UMTS)data service: High Speed Uplink/Downlink packet Access (HSDPA/HSUPA): 3 MbpsCDMA-2000: CDMA in TDMA slotsdata service: 1xEvlution Data Optimized (1xEVDO) up to 14 Mbps….. more (and more interesting) cellular topics due to mobility (stay tuned for details)6: Wireless and Mobile Networks6-41Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“wi-fi”)6.4Cellular Internet Accessarchitecturestandards (e.g., GSM)Mobility6.5 Principles: addressing and routing to mobile users6.6Mobile IP6.7Handling mobility in cellular networks6.8Mobility and higher-layer protocols6.9Summary6: Wireless and Mobile Networks6-42What is mobility?spectrum of mobility, from thenetworkperspective: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 and Mobile Networks6-43Mobility: Vocabularyhome network:permanent “home” of mobile(e.g., 128.119.40/24)Permanent address:address in home network, can alwaysbe 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 networkcorrespondent6: Wireless and Mobile Networks6-44Mobility: more vocabularyCare-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., 128.119.40.186)foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile6: Wireless and Mobile Networks6-45How do youcontact a mobile friend:search all phone books?call her parents?expect 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 Networks6-46Mobility: approachesLet routing 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-systemsLet end-systems handle it: indirect routing:communication from correspondent to mobile goes through home agent, then forwarded to remotedirect routing:correspondent gets foreign address of mobile, sends directly to mobile6: Wireless and Mobile Networks6-47Mobility: approachesLet routing 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-systemslet end-systems handle it: indirect routing:communication from correspondent to mobile goes through home agent, then forwarded to remotedirect routing:correspondent gets foreign address of mobile, sends directly to mobilenot scalableto millions ofmobiles6: Wireless and Mobile Networks6-48Mobility: registrationEnd result:Foreign agent knows about mobileHome 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 network”6: Wireless and Mobile Networks6-49Mobility 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 directly to correspondent6: Wireless and Mobile Networks6-50Indirect Routing: commentsMobile uses two addresses:permanent address:used by correspondent (hence mobile location is transparentto correspondent)care-of-address:used by home agent to forward datagrams to mobileforeign agent functions may be done by mobile itselftriangle routing:correspondent-home-network-mobileinefficient when correspondent, mobile are in same network6: Wireless and Mobile Networks6-51Indirect Routing: moving between networkssuppose mobile user moves to another networkregisters with new foreign agentnew foreign agent registers with home agenthome agent update care-of-address for mobilepackets continue to be forwarded to mobile (but with new care-of-address)mobility, changing foreign networks transparent: on going connections can be maintained!6: Wireless and Mobile Networks6-52Mobility via Direct Routingwide 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 Networks6-53Mobility via Direct Routing: commentsovercome triangle routing problemnon-transparent to correspondent:correspondent must get care-of-address from home agentwhat if mobile changes visited network?6: Wireless and Mobile Networks6-54wide area network1foreign net visited at session startanchorforeignagent24new foreignagent35correspondentagentcorrespondentnew foreignnetworkAccommodating mobility with direct routinganchor foreign agent: FA in first visited networkdata always routed first to anchor FAwhen mobile moves: new FA arranges to have data forwarded from old FA (chaining)6: Wireless and Mobile Networks6-55Chapter 6 outline6.1IntroductionWireless6.2 Wireless links, characteristicsCDMA6.3IEEE 802.11 wireless LANs (“wi-fi”)6.4Cellular Internet Accessarchitecturestandards (e.g., GSM)Mobility6.5Principles: addressing and routing to mobile users6.6 Mobile IP6.7 Handling mobility in cellular networks6.8Mobility and higher-layer protocols6.9Summary6: Wireless and Mobile Networks6-56Mobile IPRFC 3344has many features we’ve seen: home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)three components to standard:indirect routing of datagramsagent discoveryregistration with home agent6: Wireless and Mobile Networks6-57Mobile 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 agent: a packet within a packetdest: 128.119.40.186foreign-agent-to-mobile packet6: Wireless and Mobile Networks6-58Mobile IP: agent discoveryagent advertisement:foreign/home agents advertise service by broadcasting ICMP messages(typefield = 9) RBHFMGV bits reserved type = 16 type = 9 code = 0 = 9 checksum = 9 router address standard ICMP fields mobility agent advertisement extension length sequence # registration lifetime 0 or more care-of-addresses 0 8 16 24 R bit: registration requiredH,F bits: home and/or foreign agent6: Wireless and Mobile Networks6-59Mobile IP: registration example visited network: 79.129.13/24 home agent HA: 128.119.40.7 foreign agent COA: 79.129.13.2 COA: 79.129.13.2 …. ICMP agent adv. Mobile agent MA: 128.119.40.186 registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification:714 …. registration req. COA: 79.129.13.2 HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 9999 identification: 714 encapsulation format …. registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 encapsulation format …. registration reply HA: 128.119.40.7 MA: 128.119.40.186 Lifetime: 4999 Identification: 714 …. time 6: Wireless and Mobile Networks6-60Components of cellular network architecturecorrespondentMSCMSCMSCMSCMSCwired public telephonenetworkdifferent cellular networks,operated by different providersrecall:6: Wireless and Mobile Networks6-61Handling mobility in cellular networkshome network:network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon)home location register (HLR):database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network)visited network:network in which mobile currently residesvisitor location register (VLR):database with entry for each user currently in networkcould be home network6: Wireless and Mobile Networks6-62Public switched telephonenetwork mobileuserhomeMobile Switching CenterHLRhome networkvisitednetworkcorrespondentMobile Switching CenterVLRGSM: indirect routing to mobile1call routed to home network2home MSC consults HLR,gets roaming number ofmobile in visited network3home MSC sets up 2ndleg of callto MSC in visited network4MSC in visited network completescall through base station to mobile6: Wireless and Mobile Networks6-63Mobile Switching CenterVLRold BSSnew BSSold routingnewroutingGSM: handoff with common MSCHandoff goal: route call via new base station (without interruption)reasons for handoff:stronger signal to/from new BSS (continuing connectivity, less battery drain)load balance: free up channel in current BSSGSM doesn’t mandate why to perform handoff (policy), only how (mechanism)handoff initiated by old BSS6: Wireless and Mobile Networks6-64Mobile Switching CenterVLRold BSS13245678GSM: handoff with common MSCnew BSS1. old BSS informs MSC of impending handoff, provides list of 1+new BSSs 2. MSC sets up path (allocates resources) to new BSS3. new BSS allocates radio channel for use by mobile4. new BSS signals MSC, old BSS: ready 5. old BSS tells mobile: perform handoff to new BSS6. mobile, new BSS signal to activate new channel7. mobile signals via new BSS to MSC: handoff complete. MSC reroutes call8 MSC-old-BSS resources released6: Wireless and Mobile Networks6-65home networkHome MSCPSTNcorrespondentMSCanchor MSCMSCMSC(a) before handoffGSM: handoff between MSCsanchor MSC:first MSC visited during calcall remains routed through anchor MSCnew MSCs add on to end of MSC chain as mobile moves to new MSCIS-41 allows optional path minimization step to shorten multi-MSC chain6: Wireless and Mobile Networks6-66home networkHome MSCPSTNcorrespondentMSCanchor MSCMSCMSC(b) after handoffGSM: handoff between MSCsanchor MSC:first MSC visited during calcall remains routed through anchor MSCnew MSCs add on to end of MSC chain as mobile moves to new MSCIS-41 allows optional path minimization step to shorten multi-MSC chain6: Wireless and Mobile Networks6-67Mobility: GSM versus Mobile IPGSM element Comment on GSM element Mobile IP elementHome systemNetwork to which mobile user’s permanent phone number belongsHome networkGateway Mobile Switching Center, or “home MSC”. Home Location Register (HLR)Home MSC: point of contact to obtain routable address of mobile user. HLR: database in home system containing permanent phone number, profile information, current location of mobile user, subscription informationHome agentVisited SystemNetwork other than home system where mobile user is currently residingVisited networkVisited Mobile services Switching Center.Visitor Location Record (VLR)Visited MSC: responsible for setting up calls to/from mobile nodes in cells associated with MSC. VLR: temporary database entry in visited system, containing subscription information for each visiting mobile userForeign agentMobile Station Roaming Number (MSRN), or “roaming number”Routable address for telephone call segment between home MSC and visited MSC, visible to neither the mobile nor the correspondent.Care-of-address6: Wireless and Mobile Networks6-68Wireless, mobility: impact on higher layer protocolslogically, impact shouldbe minimal …best effort service model remains unchanged TCP and UDP can (and do) run over wireless, mobile… but performance-wise:packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoffTCP interprets loss as congestion, will decrease congestion window un-necessarilydelay impairments for real-time trafficlimited bandwidth of wireless links6: Wireless and Mobile Networks6-69Chapter 6 SummaryWirelesswireless links:capacity, distancechannel impairmentsCDMAIEEE 802.11 (“wi-fi”)CSMA/CA reflects wireless channel characteristicscellular accessarchitecturestandards (e.g., GSM, CDMA-2000, UMTS)Mobilityprinciples: addressing, routing to mobile usershome, visited networksdirect, indirect routingcare-of-addressescase studiesmobile IPmobility in GSMimpact on higher-layer protocols