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1、Wireless, Mobile Networks6-1Chapter 6 Wireless and Mobile NetworksBackground: v# wireless (mobile) phone subscribers now exceeds # wired phone subscribers!v# wireless Internet-connected devices soon to exceed # wireline Internet-connected deviceslaptops, Internet-enabled phones promise anytime untet
2、hered Internet accessvtwo important (but different) challengeswireless: communication over wireless linkmobility: handling the mobile user who changes point of attachment to networkWireless, Mobile Networks6-2Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 8
3、02.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Accessarchitecturestandards (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 Networks6-3Elements of a w
4、ireless networknetwork infrastructurewireless hostsvlaptop, PDA, IP phonevrun applicationsvmay be stationary (non-mobile) or mobilewireless does not always mean mobilityWireless, Mobile Networks6-4Elements of a wireless networknetwork infrastructure base stationvtypically connected to wired networkv
5、relay - responsible for sending packets between wired network and wireless host(s) in its “area”e.g., cell towers, 802.11 access points Wireless, Mobile Networks6-5Elements of a wireless networknetwork infrastructure wireless linkvtypically used to connect mobile(s) to base stationvalso used as back
6、bone link vmultiple access protocol coordinates link access vvarious data rates, transmission distanceWireless, Mobile Networks6-6Characteristics of selected wireless link standardsIndoor10-30mOutdoor50-200mMid-rangeoutdoor200m 4 KmLong-rangeoutdoor5Km 20 Km.056.384145-1154IS-95, CDMA, GSM2GUMTS/WCD
7、MA, CDMA20003G802.15802.11b802.11a,gUMTS/WCDMA-HSPDA, CDMA2000-1xEVDO3G cellularenhanced802.16 (WiMAX)802.11a,g point-to-point200802.11nData rate (Mbps)dataWireless, Mobile Networks6-7Elements of a wireless networknetwork infrastructure infrastructure modevbase station connects mobiles into wired ne
8、tworkvhandoff: mobile changes base station providing connection into wired networkWireless, Mobile Networks6-8Elements of a wireless networkad hoc modevno base stationsvnodes can only transmit to other nodes within link coveragevnodes organize themselves into a network: route among themselvesWireles
9、s, Mobile Networks6-9Wireless 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 s
10、everalwireless 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 6-10Wireless Link Characteristics (1)Differences from wired link .decreased signal strength: radio
11、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 wellmultipath propagation: radio signal reflects off objects ground, arriving a
12、d destination at slightly different times. make communication across (even a point to point) wireless link much more “difficult” Wireless, Mobile Networks 6-11Wireless Link Characteristics (2)vSNR: signal-to-noise ratiolarger SNR easier to extract signal from noise (a “good thing”)vSNR versus BER tr
13、adeoffsgiven physical layer: increase power - increase SNR-decrease BERgiven SNR: choose physical layer that meets BER requirement, giving highest thruputSNR may change with mobility: dynamically adapt physical layer (modulation technique, rate) 10203040QAM256 (8 Mbps)QAM16 (4 Mbps)BPSK (1 Mbps)SNR(
14、dB)BER10-110-210-310-510-610-710-4Wireless, Mobile Networks 6-12Wireless network characteristicsMultiple wireless senders and receivers create additional problems (beyond multiple access):ABCHidden terminal problemvB, A hear each othervB, C hear each othervA, C can not hear each othermeans A, C unaw
15、are of their interference at BABCAs signalstrengthspaceCs signalstrengthSignal attenuation:vB, A hear each othervB, C hear each othervA, C can not hear each other interfering at BWireless, Mobile Networks 6-13Code Division Multiple Access (CDMA)vused in several wireless broadcast channels (cellular,
16、 satellite, etc) standardsvunique “code” assigned to each user; i.e., code set partitioningvall users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode datavencoded signal = (original data) X (chipping sequence)vdecoding: inner-product of encoded signal and chipp
17、ing sequencevallows multiple users to “coexist” and transmit simultaneously with minimal interference (if codes are “orthogonal”)Wireless, Mobile Networks 6-14CDMA 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 -1 -slot 0channelou
18、tputslot 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=1MMWireless, Mobile Networks 6-15CDMA: two-sender interferenceWi
19、reless, Mobile Networks 6-16Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Accessarchitecturestandards (e.g., GSM)Mobility6.5 Principles: addressing and routing to mobile users6.6 Mobile IP6.7 Handling mob
20、ility in cellular networks6.8 Mobility and higher-layer protocols6.9 SummaryWireless, Mobile Networks 6-17IEEE 802.11 Wireless LANv802.11b2.4-5 GHz unlicensed spectrumup to 11 Mbpsdirect sequence spread spectrum (DSSS) in physical layerall hosts use same chipping codev802.11a 5-6 GHz rangeup to 54 M
21、bpsv802.11g 2.4-5 GHz rangeup to 54 Mbpsv802.11n: multiple antennae2.4-5 GHz rangeup to 200 Mbpsvall use CSMA/CA for multiple accessvall have base-station and ad-hoc network versionsWireless, Mobile Networks 6-18802.11 LAN architecturevwireless host communicates with base stationbase station = acces
22、s point (AP)vBasic Service Set (BSS) (aka “cell”) in infrastructure mode contains:wireless hostsaccess point (AP): base stationad hoc mode: hosts onlyBSS 1BSS 2Internethub, switchor routerAPAPWireless, Mobile Networks 6-19802.11: Channels, associationv802.11b: 2.4GHz-2.485GHz spectrum divided into 1
23、1 channels at different frequenciesAP admin chooses frequency for APinterference possible: channel can be same as that chosen by neighboring AP!vhost: must associate with an APscans channels, listening for beacon frames containing APs name (SSID) and MAC addressselects AP to associate withmay perfor
24、m authentication Chapter 8will typically run DHCP to get IP address in APs subnetWireless, Mobile Networks 6-20802.11: 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
25、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 APWireless, Mobile Networks 6-21IEEE 802.11: multiple ac
26、cessvavoid collisions: 2+ nodes transmitting at same timev802.11: CSMA - sense before transmittingdont 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 collisio
27、ns in any case: hidden terminal, fadinggoal: avoid collisions: CSMA/C(ollision)A(voidance)ABCABCAs signalstrengthspaceCs signalstrengthWireless, Mobile Networks 6-22IEEE 802.11 MAC Protocol: CSMA/CA802.11 sender1 if sense channel idle for DIFS then transmit entire frame (no CD)2 if sense channel bus
28、y then start random 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 Ne
29、tworks 6-23Avoiding 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 CSMARTSs may still collide with each other (but theyre short)vBS broadcas
30、ts clear-to-send CTS in response to RTSvCTS heard by all nodessender transmits data frameother stations defer transmissions avoid data frame collisions completely using small reservation packets!Wireless, Mobile Networks 6-24Collision Avoidance: RTS-CTS exchangeAPABtimeRTS(A)RTS(B)RTS(A)CTS(A)CTS(A)
31、DATA (A)ACK(A)ACK(A)reservation collisiondeferWireless, Mobile Networks 6-25framecontroldurationaddress1address2address4address3payloadCRC22666260 - 23124seqcontrol802.11 frame: addressingAddress 2: MAC addressof wireless host or AP transmitting this frameAddress 1: MAC addressof wireless host or AP
32、 to receive this frameAddress 3: MAC addressof router interface to which AP is attachedAddress 4: used only in ad hoc modeWireless, Mobile Networks 6-26InternetrouterAPH1R1AP MAC addr H1 MAC addr R1 MAC addraddress 1address 2address 3802.11 frameR1 MAC addr H1 MAC addr dest. address source address 8
33、02.3 frame802.11 frame: addressingWireless, Mobile Networks 6-27framecontroldurationaddress1address2address4address3payloadCRC22666260 - 23124seqcontrolTypeFromAPSubtypeToAPMore fragWEPMoredataPowermgtRetryRsvdProtocolversion22411111111802.11 frame: moreduration of reserved transmission time (RTS/CT
34、S)frame seq #(for RDT)frame type(RTS, CTS, ACK, data)Wireless, Mobile Networks 6-28hub or switchAP 2AP 1H1BBS 2BBS 1802.11: mobility within same subnetroutervH1 remains in same IP subnet: IP address can remain samevswitch: which AP is associated with H1?self-learning (Ch. 5): switch will see frame f
35、rom H1 and “remember” which switch port can be used to reach H1Wireless, Mobile Networks 6-29802.11: 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 M
36、bps)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 BERWireless, Mobile Networks 6-30802.11: advanced capabilitiesPower Managementvnode-to-AP
37、: “I am going to sleep until next beacon frame”AP knows not to transmit frames to this nodenode wakes up before next beacon framevbeacon frame: contains list of mobiles with AP-to-mobile frames waiting to be sentnode will stay awake if AP-to-mobile frames to be sent; otherwise sleep again until next
38、 beacon frameWireless, Mobile Networks 6-31Mradius 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
39、 (to master)master grants requestsv802.15: evolved from Bluetooth specification2.4-2.5 GHz radio bandup to 721 kbpsWireless, Mobile Networks 6-32802.16: WiMAXvlike 802.11 & cellular: base station modeltransmissions to/from base station by hosts with omnidirectional antennabase station-to-base statio
40、n backhaul with point-to-point antennavunlike 802.11:range 6 miles (“city rather than coffee shop”)14 Mbpspoint-to-multipointpoint-to-pointWireless, Mobile Networks 6-33802.16: WiMAX: downlink, uplink schedulingvtransmission framedown-link subframe: base station to node uplink subframe: node to base
41、 stationpream.DL-MAPUL-MAPDLburst 1SS #1DLburst 2DLburst nInitialmaint.requestconn.downlink subframeSS #2SS #kuplink subframebase station tells nodes who will get to receive (DL map) and who will get to send (UL map), and whenvWiMAX standard provide mechanism for scheduling, but not scheduling algor
42、ithmWireless, Mobile Networks 6-34Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Accessarchitecturestandards (e.g., GSM)Mobility6.5 Principles: addressing and routing to mobile users6.6 Mobile IP6.7 Handli
43、ng mobility in cellular networks6.8 Mobility and higher-layer protocols6.9 SummaryWireless, Mobile Networks 6-35Mobile Switching CenterPublic telephonenetwork, andInternetMobile Switching CenterComponents of cellular network architecturev connects cells to wide area netv manages call setup (more lat
44、er!)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 networkWireless, Mobile Networks 6-36Cellular networks: the first h
45、opTwo 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 Networks 6-37Cellular standards: brief survey2G systems: voice channelsv
46、IS-136 TDMA: combined FDMA/TDMA (North America)vGSM (global system for mobile communications): combined FDMA/TDMA most widely deployedvIS-95 CDMA: code division multiple accessIS-136GSMIS-95GPRSEDGECDMA-2000UMTSTDMA/FDMADont drown in a bowlof alphabet soup: use thisfor reference onlyWireless, Mobile
47、 Networks 6-38Cellular standards: brief survey2.5 G systems: voice and data channelsvfor those who cant wait for 3G service: 2G extensionsvgeneral packet radio service (GPRS)evolved from GSM data sent on multiple channels (if available)venhanced data rates for global evolution (EDGE)also evolved fro
48、m GSM, using enhanced modulation data rates up to 384KvCDMA-2000 (phase 1)data rates up to 144Kevolved from IS-95Wireless, Mobile Networks 6-39Cellular standards: brief survey3G systems: voice/datavUniversal Mobile Telecommunications Service (UMTS)data service: High Speed Uplink/Downlink packet Acce
49、ss (HSDPA/HSUPA): 3 MbpsvCDMA-2000: CDMA in TDMA slotsdata service: 1xEvolution Data Optimized (1xEVDO) up to 14 Mbps . more (and more interesting) cellular topics due to mobility (stay tuned for details)Wireless, Mobile Networks 6-40BSCBTSBase transceiver station (BTS)Base station controller (BSC)M
50、obile Switching Center (MSC)Mobile subscribersBase station system (BSS)Legend2G (voice) network architecture MSCPublic telephonenetworkGatewayMSCGWireless, Mobile Networks 6-412.5G (voice+data) network architectureBSCMSCSGSNPublic telephonenetworkGatewayMSCGServing GPRS Support Node (SGSN)Gateway GP
51、RS Support Node (GGSN)Public InternetGGSNGKey insight: new cellular datanetwork operates in parallel (except at edge) with existing cellular voice networkq voice network unchanged in coreq data network operates in parallelWireless, Mobile Networks 6-42Chapter 6 outline6.1 Introduction Wireless6.2 Wi
52、reless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 Cellular Internet Accessarchitecturestandards (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 Summary
53、Wireless, Mobile Networks 6-43What is mobility?vspectrum 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 (like cell phone)mobile user, connecting/ d
54、isconnecting from network using DHCP. Wireless, Mobile Networks 6-44Mobility: 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 agent: entity that will perform mobility functio
55、ns on behalf of mobile, when mobile is remotewide area networkcorrespondentWireless, Mobile Networks 6-45Mobility: 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
56、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 mobileWireless, Mobile Networks 6-46How do you contact a mobile friend:vsearch all phone books?vcall her parents?vex
57、pect 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 6-47Mobility: approachesvLet routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table
58、 exchange.routing tables indicate where each mobile locatedno 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 t
59、o mobileWireless, Mobile Networks 6-48Mobility: approachesvLet routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange.routing tables indicate where each mobile locatedno changes to end-systemsvlet end-systems handle it: indirect routing:
60、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 mobilesWireless, Mobile Networks 6-49Mobility: registrationEnd result:vForeign agent knows abo
61、ut mobilevHome 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”Wireless, Mobile Networks 6-50Mobility via Indirect Routingwide area netw
62、orkhomenetworkvisitednetwork3241correspondent addresses packets using home address of mobilehome agent intercepts packets, forwards to foreign agentforeign agent receives packets, forwards to mobilemobile replies directly to correspondentWireless, Mobile Networks 6-51Indirect Routing: commentsvMobil
63、e uses two addresses:permanent address: used by correspondent (hence mobile location is transparent to correspondent)care-of-address: used by home agent to forward datagrams to mobilevforeign agent functions may be done by mobile itselfvtriangle routing: correspondent-home-network-mobileinefficient
64、when correspondent, mobile are in same networkWireless, Mobile Networks 6-52Indirect Routing: moving between networksvsuppose mobile user moves to another networkregisters with new foreign agentnew foreign agent registers with home agenthome agent update care-of-address for mobilepackets continue to
65、 be forwarded to mobile (but with new care-of-address)vmobility, changing foreign networks transparent: on going connections can be maintained!Wireless, Mobile Networks 6-53Mobility via Direct Routingwide area networkhomenetworkvisitednetwork4241correspondent requests, receives foreign address of mo
66、bilecorrespondent forwards to foreign agentforeign agent receives packets, forwards to mobilemobile replies directly to correspondent3Wireless, Mobile Networks 6-54Mobility via Direct Routing: commentsvovercome triangle routing problemvnon-transparent to correspondent: correspondent must get care-of
67、-address from home agentwhat if mobile changes visited network?Wireless, Mobile Networks 6-55wide area network1foreign net visited at session startanchorforeignagent24new foreignagent35correspondentagentcorrespondentnew foreignnetworkAccommodating mobility with direct routingvanchor foreign agent: F
68、A in first visited networkvdata always routed first to anchor FAvwhen mobile moves: new FA arranges to have data forwarded from old FA (chaining)Wireless, Mobile Networks 6-56Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802.11 wireless LANs (“Wi-Fi”)6.4 C
69、ellular Internet Accessarchitecturestandards (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 Networks 6-57Mobile IPvRFC 3344vhas many features weve seen:
70、 home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet)vthree components to standard:indirect routing of datagramsagent discoveryregistration with home agentWireless, Mobile Networks 6-58Mobile IP: indirect routingPermanent address: 128.119
71、.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 packetWireless, Mobile Networks 6-59Mobile IP: agent discoveryvagent
72、 advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9)R bit: registration requiredH,F bits: home and/or foreign agentWireless, Mobile Networks 6-60Mobile IP: registration exampleWireless, Mobile Networks 6-61Components of cellular network architecturecorr
73、espondentMSCMSCMSCMSCMSCwired public telephonenetworkdifferent cellular networks,operated by different providersrecall:Wireless, Mobile Networks 6-62Handling mobility in cellular networksvhome network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon)home location register (H
74、LR): database in home network containing permanent cell phone #, profile information (services, preferences, billing), information about current location (could be in another network)vvisited network: network in which mobile currently residesvisitor location register (VLR): database with entry for e
75、ach user currently in networkcould be home networkWireless, Mobile Networks 6-63Public switched telephonenetwork mobileuserhomeMobile Switching CenterHLRhome networkvisitednetworkcorrespondentMobile Switching CenterVLRGSM: indirect routing to mobile1call routed to home network2home MSC consults HLR,
76、gets roaming number ofmobile in visited network3home MSC sets up 2nd leg of callto MSC in visited network4MSC in visited network completescall through base station to mobileWireless, Mobile Networks 6-64Mobile Switching CenterVLRold BSSnew BSSold routingnewroutingGSM: handoff with common MSCvHandoff
77、 goal: route call via new base station (without interruption)vreasons for handoff:stronger signal to/from new BSS (continuing connectivity, less battery drain)load balance: free up channel in current BSSGSM doesnt mandate why to perform handoff (policy), only how (mechanism)vhandoff initiated by old
78、 BSSWireless, Mobile Networks 6-65Mobile 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 s
79、ignals 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 releasedWireless, Mobile Networks 6-66home networkHome MSCPSTNcorrespondentM
80、SCanchor MSCMSCMSC(a) before handoffGSM: handoff between MSCsvanchor MSC: first MSC visited during calcall remains routed through anchor MSCvnew MSCs add on to end of MSC chain as mobile moves to new MSCvIS-41 allows optional path minimization step to shorten multi-MSC chainWireless, Mobile Networks
81、 6-67home networkHome MSCPSTNcorrespondentMSCanchor MSCMSCMSC(b) after handoffGSM: handoff between MSCsvanchor MSC: first MSC visited during calcall remains routed through anchor MSCvnew MSCs add on to end of MSC chain as mobile moves to new MSCvIS-41 allows optional path minimization step to shorte
82、n multi-MSC chainWireless, Mobile Networks 6-68Mobility: GSM versus Mobile IPGSM element Comment on GSM element Mobile IP elementHome systemNetwork to which mobile users permanent phone number belongsHome networkGateway Mobile Switching Center, or “home MSC”. Home Location Register (HLR)Home MSC: po
83、int 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 residingVisite
84、d 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 ag
85、entMobile 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-addressWireless, Mobile Networks 6-69Wireless, mobility: impact on higher layer protocolsvlogically, i
86、mpact should be minimal best effort service model remains unchanged TCP and UDP can (and do) run over wireless, mobilev but performance-wise:packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoffTCP interprets loss as congestion, will decrease con
87、gestion window un-necessarilydelay impairments for real-time trafficlimited bandwidth of wireless linksWireless, Mobile Networks 6-70Chapter 6 SummaryWirelessvwireless links:capacity, distancechannel impairmentsCDMAvIEEE 802.11 (“Wi-Fi”)CSMA/CA reflects wireless channel characteristicsvcellular accessarchitecturestandards (e.g., GSM, CDMA-2000, UMTS)Mobilityvprinciples: addressing, routing to mobile usershome, visited networksdirect, indirect routingcare-of-addressesvcase studiesmobile IPmobility in GSMvimpact on higher-layer protocols
