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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 deviceslaptops, Internet-enabled phones promise anyti
5、me 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, characteristicsCDMA6.
6、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 SummaryWireless, Mobile Networks6-4Element
7、s of a wireless networknetwork infrastructureWireless, Mobile Networks6-5wireless hostsvlaptop, smartphonevrun applicationsvmay be stationary (non-mobile) or mobilewireless does not always mean mobilityElements of a wireless networknetwork infrastructureWireless, Mobile Networks6-6 base stationvtypi
8、cally 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 mobile(s)
9、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-rangeoutdoor2
10、00m 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 mobiles in
11、to 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 a net
12、work: 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 to larg
13、er 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 Introdu
14、ction 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 mobility in cellular networks6.8 Mobility and higher-layer
15、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 (e.g., 2.
16、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” Wireless, Mobile
17、 Networks 6-14Wireless Link Characteristics (2)vSNR: signal-to-noise ratiolarger 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, giving highes
18、t thruputSNR 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 receivers create ad
19、ditional 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 othervA, C can n
20、ot hear each other interfering at BWireless, Mobile Networks 6-16Code Division Multiple Access (CDMA)vunique “code” assigned to each user; i.e., code set partitioningall users share same frequency, but each user has own “chipping” sequence (i.e., code) to encode dataallows multiple users to “coexist
21、” 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 -Zi,m= di.cmd0
22、 = 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
23、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 Introduction
24、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 mobility in cellular networks6.8 Mobility and higher-layer protoc
25、ols6.9 SummaryWireless, Mobile Networks 6-20IEEE 802.11 Wireless LAN802.11bv2.4-5 GHz unlicensed spectrumvup to 11 Mbpsvdirect sequence spread spectrum (DSSS) in physical layerall hosts use same chipping code802.11a 5-6 GHz rangeup to 54 Mbps802.11g 2.4-5 GHz rangeup to 54 Mbps802.11n: multiple ante
26、nnae2.4-5 GHz rangeup 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 stationbase station = access point (AP)vBasic Service Set (BSS) (aka “cell”) in infrastruc
27、ture mode contains:wireless hostsaccess point (AP): base stationad 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 frequenciesAP admin chooses frequency for A
28、Pinterference 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 perform authentication Chapter 8will typically run DHCP to get IP address
29、 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 1H1BBS 2BBS 112234active scanning: (
30、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+ nodes transmitting at same timev8
31、02.11: 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 collisions in any case: hidden terminal, fadinggoal: avoid collisio
32、ns: 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 backoff timetimer counts down while cha
33、nnel 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 collisions (more)idea: allow sender to
34、“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 broadcasts clear-to-send CTS in response to RTSvCTS heard by all no
35、dessender transmits data frameother 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(A)reservation collisiondeferWireless, Mob
36、ile 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 frameAddress 3: MAC addressof router inter
37、face 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 frame: addressingWireless, Mobile Networks 6
38、-30framecontroldurationaddress1address2address4address3payloadCRC22666260 - 23124seqcontrolTypeFromAPSubtypeToAPMore fragWEPMoredataPowermgtRetryRsvdProtocolversion22411111111duration of reserved transmission time (RTS/CTS)frame seq #(for RDT)frame type(RTS, CTS, ACK, data)802.11 frame: moreWireless
39、, 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 reach H1H1BBS 2BBS 1Wireless, Mobile Networks
40、 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)BER10-110-210-310-510-610-710-4operating point1. SNR decreases, BER i
41、ncrease 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 frames to this nodenode wakes up before next
42、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 beacon frame802.11: advanced capabilitiesWireless, Mobile Networks 6-34Mradius ofcoverageSSSPPPPMSMaster deviceSlave
43、 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 requestsv802.15: evolved from Bluetooth specification2.4-2.5 G
44、Hz radio bandup to 721 kbpsWireless, Mobile Networks 6-35Chapter 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 users
45、6.6 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 architecturev connects cells to wired tel. net.v manages call set
46、up (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 networkWireless, Mobile Networks 6-37Cellular networks:
47、 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 Networks 6-38BSCBTSBase transceiver station (BTS)Base statio
48、n 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 controllerMSCSGSNPublic telephonenetworkGatewayMSCGServi
49、ng 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 in parallelWireless, Mobile Networks 6-40radionetwor
50、k controllerMSCSGSNPublic telephonenetworkGatewayMSCGPublic InternetGGSNGradio access networkUniversal Terrestrial Radio Access Network (UTRAN)core networkGeneral Packet Radio Service (GPRS) Core NetworkpublicInternetradio interface(WCDMA, HSPA)3G (voice+data) network architectureWireless, Mobile Ne
51、tworks 6-41Chapter 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 mobility in cellular
52、 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, passing through multiple access point while maintaining ongo
53、ing 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: address in home network, can always be used to reach mob
54、ilee.g., 128.119.40.186home 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., 79,129.13.2) visited network: network in which mobile cu
55、rrently 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 mobileWireless, Mobile Networks 6-45How do you contact a mobile friend
56、: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 routing handle it: routers advertise permanent address of mob
57、ile-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: communication from correspondent to mobile goes through home agent, then forwarded to remotedirect routing: correspondent ge
58、ts 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 mobile locatedno changes to end-systemsvlet end-systems han
59、dle 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 mobilesMobility: approacheswide area networkWireless, Mobile Network
60、s 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 mobile is resident in my network”Wireless, Mobile Networks 6
61、-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 correspondentWireless, Mobile
62、 Networks 6-50Indirect Routing: commentsvmobile 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:
63、 correspondent-home-network-mobileinefficient when correspondent, mobile are in same networkWireless, Mobile Networks 6-51Indirect routing: moving between networksvsuppose mobile user moves to another networkregisters with new foreign agentnew foreign agent registers with home agenthome agent update
64、 care-of-address for mobilepackets continue to be forwarded to mobile (but with new care-of-address)vmobility, changing foreign networks transparent: on going connections can be maintained!1234Wireless, Mobile Networks 6-52Mobility via direct routinghomenetworkvisitednetworkcorrespondent requests, r
65、eceives foreign address of mobilecorrespondent forwards to foreign agentforeign agent receives packets, forwards to mobilemobile replies directly to correspondentWireless, Mobile Networks 6-53Mobility via direct routing: commentsvovercome triangle routing problemvnon-transparent to correspondent: co
66、rrespondent must get care-of-address from home agentwhat if mobile changes visited network?1234Wireless, Mobile Networks 6-54wide area network1foreign net visited at session startanchorforeignagent24new foreignagent3correspondentagentcorrespondentnew foreignnetworkAccommodating mobility with direct
67、routingvanchor foreign agent: FA in first visited networkvdata always routed first to anchor FAvwhen mobile moves: new FA arranges to have data forwarded from old FA (chaining)5Wireless, Mobile Networks 6-55Chapter 6 outline6.1 Introduction Wireless6.2 Wireless links, characteristicsCDMA6.3 IEEE 802
68、.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 Networks 6-56Mobile IPvRFC 3
69、344vhas many features weve seen: 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 6-57Mobile IP: indirect r
70、outingPermanent 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 packetWireless, Mobile Networks 6-58
71、Mobile IP: agent discoveryvagent 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 6-59Mobile IP: registration examplevisited network: 79.129.13/24home agentHA: 12
72、8.119.40.7foreign agentCOA: 79.129.13.2mobile agentMA: 128.119.40.186registration req. COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186Lifetime: 9999identification:714.registration reply HA: 128.119.40.7MA: 128.119.40.186Lifetime: 4999Identification: 714encapsulation format.registration reply HA:
73、128.119.40.7MA: 128.119.40.186Lifetime: 4999Identification: 714.timeICMP agent adv.COA: 79.129.13.2.registration req. COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186Lifetime: 9999identification: 714encapsulation format.Wireless, Mobile Networks 6-60Components of cellular network architecturecorre
74、spondentMSCMSCMSCMSCMSCwired public telephonenetworkdifferent cellular networks,operated by different providersrecall:Wireless, Mobile Networks 6-61Handling mobility in cellular networksvhome network: network of cellular provider you subscribe to (e.g., Sprint PCS, Verizon)home location register (HL
75、R): 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 ea
76、ch user currently in networkcould be home networkWireless, Mobile Networks 6-62Public switched telephonenetwork mobileuserhomeMobile Switching CenterHLRhome networkvisitednetworkcorrespondentMobile Switching CenterVLRGSM: indirect routing to mobile1call routed to home network2home MSC consults HLR,g
77、ets 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 6-63Mobile Switching CenterVLRold BSSnew BSSold routingnewroutingGSM: handoff with common MSCvhandoff
78、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
79、BSSWireless, Mobile Networks 6-64Mobile Switching CenterVLRold BSS13245678new 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.
80、 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 releasedGSM: handoff with common MSCWireless, Mobile Networks 6-65home networkHome MSCPSTNcorrespondentMS
81、Canchor MSCMSCMSC(a) before handoffGSM: handoff between MSCsvanchor MSC: first MSC visited during callcall remains routed through anchor MSCvnew MSCs add on to end of MSC chain as mobile moves to new MSCvoptional path minimization step to shorten multi-MSC chainWireless, Mobile Networks 6-66home net
82、workHome MSCPSTNcorrespondentMSCanchor MSCMSCMSC(b) after handoffvanchor MSC: first MSC visited during callcall remains routed through anchor MSCvnew MSCs add on to end of MSC chain as mobile moves to new MSCvoptional path minimization step to shorten multi-MSC chainGSM: handoff between MSCsWireless
83、, Mobile Networks 6-67Mobility: 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: point of contact to obtain
84、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 s
85、ervices 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
86、 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 6-68Wireless, mobility: impact on higher layer protocolsvlogically, impact should be minimal b
87、est 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 congestion window un-necessa
88、rilydelay impairments for real-time trafficlimited bandwidth of wireless linksWireless, Mobile Networks 6-69Chapter 6 summaryWirelessvwireless links:capacity, distancechannel impairmentsCDMAvIEEE 802.11 (“Wi-Fi”)CSMA/CA reflects wireless channel characteristicsvcellular accessarchitecturestandards (e.g., GSM, 3G, 4G LTE)Mobilityvprinciples: addressing, routing to mobile usershome, visited networksdirect, indirect routingcare-of-addressesvcase studiesmobile IPmobility in GSMvimpact on higher-layer protocols
