Chapter 6 Wireless And Mobile Networks - Cs.mun.ca
Chapter 6Wireless andMobile 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 see the animations; 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 onlyask the following:v If you use these slides (e.g., in a class) that you mention their source(after all, we’d like people to use our book!)v If you post any slides on a www site, that you note that they are adaptedfrom (or perhaps identical to) our slides, and note our copyright of thismaterial.ComputerNetworking: A TopDown Approach6th editionJim Kurose, Keith RossAddison-WesleyMarch 2012Thanks and enjoy! JFK/KWRAll material copyright 1996-2012J.F Kurose and K.W. Ross, All Rights ReservedWireless, Mobile Networks6-1Ch. 6: Wireless and Mobile NetworksBackground:v v # wireless (mobile) phone subscribers now exceeds #wired phone subscribers (5-to-1)!# wireless Internet-connected devices equals #wireline Internet-connected devices§ laptops, Internet-enabled phones promise anytime untetheredInternet accessv two important (but different) challenges§ wireless: communication over wireless link§ mobility: handling the mobile user who changes point ofattachment to networkWireless, Mobile Networks6-21
Elements of a wireless networknetworkinfrastructureWireless, Mobile Networks6-3Elements of a wireless networkwireless hostsv v v networkinfrastructurelaptop, smartphonerun applicationsmay be stationary (nonmobile) or mobile§ wireless does not alwaysmean mobilityWireless, Mobile Networks6-42
Elements of a wireless networkbase stationv v networkinfrastructuretypically connected towired networkrelay - responsible forsending packets betweenwired network andwireless host(s) in its“area”§ e.g., cell towers,802.11 access pointsWireless, Mobile Networks6-5Elements of a wireless networkwireless linkv v networkinfrastructurev v typically used to connectmobile(s) to base stationalso used as backbonelinkmultiple access protocolcoordinates link accessvarious data rates,transmission distanceWireless, Mobile Networks6-63
Characteristics of selected wireless linksData rate (Mbps)200545-11802.11n802.11a,g41802.11a,g point-to-point802.11b4G: LTWE WIMAX3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO802.15.3842.5G: UMTS/WCDMA, CDMA2000.0562G: IS-95, CDMA, rangeoutdoor200m – 4 Km5Km – 20 KmWireless, Mobile Networks6-7Elements of a wireless networkinfrastructure modev v networkinfrastructurebase station connectsmobiles into wirednetworkhandoff: mobile changesbase station providingconnection into wirednetworkWireless, Mobile Networks6-84
Elements of a wireless networkad hoc modev no base stationsv nodes can onlytransmit to othernodes within linkcoveragev nodes organizethemselves into anetwork: routeamong themselvesWireless, Mobile Networks6-9Wireless network taxonomysingle hopinfrastructure(e.g., APs)noinfrastructurehost connects tobase station (WiFi,WiMAX, cellular)which connects tolarger Internetno base station, noconnection to largerInternet (Bluetooth,ad hoc nets)multiple hopshost may have torelay through severalwireless nodes toconnect to largerInternet: mesh netno base station, noconnection to largerInternet. May have torelay to reach othera given wireless nodeMANET,VANETWireless, Mobile Networks 6-105
Wireless Link Characteristics (1)important differences from wired link .§ decreased signal strength: radio signal attenuates as itpropagates through matter (path loss)§ interference from other sources: standardized wirelessnetwork frequencies (e.g., 2.4 GHz) shared by otherdevices (e.g., phone); devices (motors) interfere aswell§ multipath propagation: radio signal reflects off objectsground, arriving ad destination at slightly differenttimes . make communication across (even a point to point)wireless link much more “difficult”Wireless, Mobile Networks 6-11Wireless Link Characteristics (2)v SNR: signal-to-noise ratio10-1§ larger SNR – easier toextract signal from noise (a“good thing”)SNR versus BER tradeoffs§ given physical layer: increasepower - increase SNR decrease BER§ given SNR: choose physical layerthat meets BER requirement,giving highest thruput SNR may change withmobility: dynamically adaptphysical layer (modulationtechnique, rate)10-3BERv 10-210-410-510-610-710203040SNR(dB)QAM256 (8 Mbps)QAM16 (4 Mbps)BPSK (1 Mbps)Wireless, Mobile Networks 6-126
Wireless network characteristicsMultiple wireless senders and receivers create additionalproblems (beyond multiple access):BACCABHidden terminal problemv v v B, A hear each otherB, C hear each otherA, C can not hear each othermeans A, C unaware of theirinterference at BC’s signalstrengthA’s signalstrengthspaceSignal attenuation:v v v B, A hear each otherB, C hear each otherA, C can not hear each otherinterfering at BWireless, Mobile Networks 6-13IEEE 802.11 Wireless LAN802.11bv 2.4-5 GHz unlicensed spectrumv up to 11 Mbpsv direct sequence spread spectrum(DSSS) in physical layer§ all hosts use same chippingcodev v 802.11a§ 5-6 GHz range§ up to 54 Mbps802.11g§ 2.4-5 GHz range§ up to 54 Mbps802.11n: multiple antennae§ 2.4-5 GHz range§ up to 200 Mbpsall use CSMA/CA for multiple accessall have base-station and ad-hoc network versionsWireless, Mobile Networks 6-147
802.11 LAN architecturev Internetwireless hostcommunicates with basestation§ base station access point(AP)hub, switchor routerv Basic Service Set (BSS) (aka“cell”) in infrastructuremode contains:§ wireless hosts§ access point (AP): basestation§ ad hoc mode: hosts onlyBSS 1BSS 2Wireless, Mobile Networks 6-15802.11 WLANv 802.11 WLAN components§ Access Point (AP) Mobile Stations (STA) Distribution System(DS)v 802.11 WLAN Modes§ BSS – basic service set (infrastructure mode) ESS – extended service set (multiple AP’s)§ IBSS – independent BSS (ad hoc mode)8
IEEE 802.11– Scope of StandardUpper layer protocols of OSIData link layerMedium Access Control (MAC)PHYFH, DS, IR, OFDM, MIMOPhysical layerIEEE 802.11Logic Layer Control (LLC) – 802.2IEEE 802.11 Early Family Members802.11(legacy)-19972Mbps/2.4GHzYr 1999802.11a - 199954Mbps/5.2GHz54MbpsOFDM802.11eQoS802.11b – 199911Mbps/2.4GHz2.4GHz802.11g - .11nMIMO9
802.11: Channels, associationv 802.11b: 2.4GHz-2.485GHz spectrum divided into 14channels at different frequencies§ AP admin chooses frequency for AP§ interference possible: channel can be same as thatchosen by neighboring AP!v host: must associate with an AP§ scans channels, listening for beacon frames containingAP’s name (SSID) and MAC address§ selects AP to associate with§ may perform authentication§ will typically run DHCP to get IP address in AP’ssubnetWireless, Mobile Networks 6-192.4 GHz ISM Band Channelization10
2.4 GHz ISM Band Channelization802.11: passive/active scanningBBS 1AP 1BBS 1BBS 2112BBS 21AP 2AP 12323AP 24H1H1passive scanning:active scanning:(1) beacon frames sent from APs(2) association Request frame sent: H1 toselected AP(3) association Response frame sent fromselected AP to H1(1) Probe Request frame broadcastfrom H1(2) Probe Response frames sentfrom APs(3) Association Request frame sent:H1 to selected AP(4) Association Response frame sentfrom selected AP to H1Wireless, Mobile Networks 6-2211
IEEE 802.11 LegacyStandardized by the .11 Working Groupv 1-2Mbps wireless LANv Multiple PHY layer choicesv Centralized and ad hoc controlv Great start pointv PHY – Physical Layer (legacy)v Diffused Infrared (IR)2.4 2.483GHz ISM band:v Frequency-Hopping Spread Spectrum (FHSS)§ Dwell time 20µs§ 79 1MHz channels with 22 hopping patternsv Direct-Sequence Spread Spectrum (DSSS)§ Barker sequence – 11-bit chipping sequence§ 14 partially overlapping 22MHz channels Center frequencies 5MHz apart§ Channels 1 11 available in N. America 1, 6, 11 can operate at the same time with 25 MHz apart12
PHY – Physical Layer (cont’d)v HR-DSSS (802.11b)§ CCK (Complementary Code Keying)v OFDM (802.11 a/g/p)§ Using multiple subcarriers at the same timev MIMO (802.11n/ac)§ Multiple simultaneous transmitters and receiversMAC Main Requirementsv Single MAC to support multiple PHYs§ Support single and multiple channel PHYs§ and PHYs with different Medium Sense Characteristicsv Should allow overlap of multiple networks in the same area andchannel space§ Need to be able to share the medium§ Allow re-use of the same mediumv Need to be robust for interference§ Microwave interferers§ Other un-licensed spectrum users§ Co-channel interferencev v v Need mechanisms to deal with Hidden TerminalsNeed provisions for Time Bounded ServicesNeed provisions for Privacy and Access Control13
IEEE 802.11: multiple accessv v avoid collisions: 2 nodes transmitting at same time802.11: CSMA - sense before transmitting§ don’t collide with ongoing transmission by other nodev 802.11: no collision detection!§ difficult to receive (sense collisions) when transmitting due to weakreceived signals (fading)§ can’t sense all collisions in any case: hidden terminal, fading§ goal: avoid collisions: CSMA/C(ollision)A(voidance)ABACBCC’s signalstrengthA’s signalstrengthspaceWireless, Mobile Networks 6-27IEEE 802.11 MAC Protocol: CSMA/CA802.11 sender1 if sense channel idle for DIFS thensendertransmit entire frame (no CD)2 if sense channel busy thenDIFSstart random backoff timetimer counts down while channel idletransmit when timer expiresif no ACK, increase random backoff interval,repeat 2802.11 receiver- if frame received OKreceiverdataSIFSACKreturn ACK after SIFS (ACK needed due tohidden terminal problem)Wireless, Mobile Networks 6-2814
Coordination Functionsv PCF – Point Coordination Function§ Infrastructure mode§ Optionalv DCF – Distributed Coordination Function§ Infrastructure and ad hoc modes§ Mandatory§ MAC protocol intended to implement ad hocnetworksv Implement different fixed priority levels§ DIFS – distributed inter-frame space§ PIFS – point inter-frame space§ SIFS – short inter-frame spaceCSMA/CA Explainedv Reduce collision probability where mostly needed§ STAs are waiting for medium to become free for longer than DIFS CCA from PHY and virtual carrier sense§ Select random backoff in current collision window after a defer, resolvingcontention to avoid collisionsv Efficient backoff algorithm stable at high loads§ Exponential contention window increases for retransmissions (up to max limit)§ Resets to min value when transmission succeeds15
CSMA/CA ACKv v Receiver sends ACK after receiving frame with correct CRCDirect access when medium is sensed free for longer than SIFS§ No random backoff neededv SIFS DISF to give ACK higher priority than a new transmission ofdata frame§ Such technique of using different inter-frame spaces to differentiatepriorities is extensively used in 802.11 MACHidden Terminal ProblemA, B, C – three nodesv B can talk to A and C directly, but A and C can’ttalk to each otherv When A transmits to B, node C, not aware of theongoing transmission, may transmit and collidewith A’s transmissionv ABC16
Exposed Terminal ProblemA, B, C, D – four nodesv Only AB, BC, and CD can talk to each otherdirectlyv When B transmits to A, node C, aware of theongoing transmission, can’t transmit to D, eventhough there will not be interference at Dv ABCDAvoiding collisions (more)idea: allow sender to “reserve” channel rather than randomaccess of data frames: avoid collisions of long data framesv sender first transmits small request-to-send (RTS) packetsto BS using CSMA§ RTSs may still collide with each other (but they’re short)v v BS broadcasts clear-to-send CTS in response to RTSCTS heard by all nodes§ sender transmits data frame§ other stations defer transmissionsavoid data frame collisions completelyusing small reservation packets!Wireless, Mobile Networks 6-3417
Collision Avoidance: RTS-CTS exchangeABAPRTS(B)RTS(A)reservation collisionRTS(A)CTS(A)CTS(A)DATA (A)defertimeACK(A)ACK(A)Wireless, Mobile Networks 6-35Hidden Terminal Resolutionv v v Duration fields in RTS and CTS frames distributes mediumreservation information, stored in an overhearing node’s counter –Network Allocation Vector (NAV)Medium “busy” decided by CCA and NAVUse of RTS/CTS is optional but must be implemented§ Use is controlled by an RTS Threshold parameter in each STA to limitoverhead18
Optional Point Coordination Function (PCF)v Contention-free service uses PCF on a DCF foundation§ PCF can provide lower transfer delay variations to support time boundedservices§ Async data, voice or mixed implementations are possible§ Point Coordinator resides in APv Coexistence of contention and optional contention-free does notburden the implementationContention Free Operationv v Alternating contention-free and contention operationunder PCF controlNAV prevents contention traffic until reset by the lastPCF transfer§ Thus, variable length of contention-free period per intervalv Both PCF and DCF defer to each other19
PCF Burstv v v v v v CF-burst by “polling” bit set in CF Down framesImmediate (w/SIFS) response by STA on CF pollSTAs to maintain NAV to protect CF trafficResponses can be of variable length“reset NAV” by last (CF End) frame from AP“ACK Previous Frame” bit in headersFragment Burstv v Long MSDU (MAC Service Data Unit) fragmentedBurst of fragments are ACKed individually§ Separated by SIFSs§ Unicast frames onlyv Random backoff and retransmission of failing fragment when no ACKis returnedv Duration information in data fragments and ACKs causes NAV to beset, for medium reservation§ Can be interrupted when missing ACK20
802.11 frame: addressing226662frameaddress address addressdurationcontrol123Address 1: MAC addressof wireless host or APto receive this frameAddress 2: MAC addressof wireless host or APtransmitting this frame6seq address4control0 - 23124payloadCRCAddress 4: used only inad hoc modeAddress 3: MAC addressof router interface towhich AP is attachedWireless, Mobile Networks 6-41802.11 frame: addressingR1 routerH1InternetR1 MAC addr H1 MAC addrdest. addresssource address802.3 frameAP MAC addr H1 MAC addr R1 MAC addraddress 1address 2address 3802.11 frameWireless, Mobile Networks 6-4221
802.11 frame: moreframe seq #(for RDT)duration of reservedtransmission time (RTS/CTS)226662Protocolversion2Type62frameaddress address addressdurationcontrol123seq address4control4111SubtypeToAPFromAPMorefrag110 - 23124payloadCRC1Power MoreRetrymgtdata11WEPRsvdframe type(RTS, CTS, ACK, data)Wireless, Mobile Networks 6-43Support for Mobility22
MAC Management Layerv Synchronization§ Finding and staying with a WLAN§ Synchronization functions TSF timer, beacon generationv Power management§ Sleeping without missing any message§ Power management functions Periodic sleep, frame buffering, traffic indication mapv Association and de-association§ Joining a network§ Roaming – moving from AP to AP§ Scanning802.11: mobility within same subnetH1 remains in sameIP subnet: IP addresscan remain samev switch: which AP isassociated with H1?v § self-learning (Ch. 5):switch will see framefrom H1 and“remember” whichswitch port can beused to reach H1BBS 1H1BBS 2Wireless, Mobile Networks 6-4623
Synchronization in 802.11Timing Synchronization Function (TSF)v Used for power managementv § Beacons sent at well known intervals§ All STA timers in BSS are synchronizedv Used for PCF timing§ To predict CP/CFP alternation periodv Used for hop timing for FH PHY§ Dwell interval§ STA synchronizationSynchronization Approachv v Each STA maintains a local timerTiming Synchronization Function (TSF)§ Keeps timers from all STAs in synch§ AP controls timing in infrastructure mode§ Distributed function for ad hoc modev Timing conveyed by periodic beacon transmissions§ § § § Beacons contain timestamps for the BSSTimestamps in beacons used to calibrate local clocksNot required to hear each beaconBeacons contain other management information Also used in power management and roaming24
Infrastructure Beacon Generationv v v AP’s send beacons in infrastructure modeBeacons scheduled at beacon intervalsTransmission may be delayed by CSMA deferral§ Subsequent transmissions at expected beacon interval§ Not relative to last transmission§ Next beacon sent at target beacon transmission timev Timestamps contains timer values at transmit time802.11: advanced capabilitiesRate adaptationbase station, mobiledynamically changetransmission rate(physical layer modulationtechnique) as mobilemoves, SNR variesQAM256 (8 Mbps)QAM16 (4 Mbps)BPSK (1 Mbps)operating point10-210-3BERv 10-110-410-510-610-7102030SNR(dB)401. SNR decreases, BERincrease as node movesaway from base station2. When BER becomes toohigh, switch to lowertransmission rate but withlower BERWireless, Mobile Networks 6-5025
802.11: advanced capabilitiespower managementv node-to-AP: “I am going to sleep until nextbeacon frame”§ AP knows not to transmit frames to this node§ node wakes up before next beacon framev beacon frame: contains list of mobiles with APto-mobile frames waiting to be sent§ node will stay awake if AP-to-mobile frames to besent; otherwise sleep again until next beacon frameWireless, Mobile Networks 6-51Infrastructure Power Managementv Broadcast frames also buffered in AP§ All broadcasts/multicasts are buffered§ Broadcasts/multicasts only sent after DTIM§ Delivery TIM – sent every several TIM intervalsv v STAs wakeup prior to an expected (D)TIMIf (D)TIM indicates frame buffered§ STA sends PS Poll and stays awake for the TIM interval toreceive data§ Else STA sleeps again26
MAC Management Framesv Beacon§ Timestamp, beacon interval, capabilities, ESSID, supported rates,parameters§ TIMv Probe§ ESSID, capabilities, supported ratesv Probe response§ Timestamp, beacon interval, capabilities, ESSID, supported rates,parameters§ Same as beacon except for TIMv Association request§ Capabilities, listen interval, ESSID, supported ratesv Association response§ Capabilities, status code, STA ID, supported ratesMore MAC Management Framesv Re-association request§ capabilities, listen interval, ESSID, supported rates,current AP addressv Re-association response§ capabilities, status code, STA ID, supported ratesv Disassociation§ Reason codev Authentication§ Algorithm, sequence, status, challenge textv De-authentication§ Reason27
PHY Amendments and Dependency---- 2012MAC Amendments and Dependency28
HIPERLAN & HIPERLAN/2v ETSI’s Project BRAN§ § § § v High performance radio LANFrequency band: 5.2GHz U-NIIVer. 1 (1997): 23.5MbpsVer. 2 (2000): 54MbpsComponents:§ Distribution System (DS)§ Access Point (AP)§ Mobile Terminal (MT)HIPERLAN & HIPERLAN/2v PHY§ OFDM (like 802.11a and g)v MAC§ TDMA/TDD§ Under control of an AP or CC (central controller,regular MT acting as AP)§ Transmission through AP/CC or directly betweenMT’s§ Better QoS provisioning29
IEEE 802.15 Working Groupv Personal Area Network (PAN)§ Communication within a person’s operating spaceIEEE 802.15.1 – Bluetoothv IEEE 802.15.3a – High data rate (UWB)v IEEE 802.15.4 – Low energy (ZigBee)v (802.15.2 – interoperability between 802.15 and802.11)v 802.15.1: personal area networkv v v v less than 100 m diameterreplacement for cables (mouse,keyboard, headphones)ad hoc: no infrastructuremaster/slaves:§ slaves request permission to send(to master)§ master grants requestsv 802.15.1: evolved fromBluetooth specification§ 2.4-2.5 GHz radio band§ up to 721 kbpsPSPradius ofcoverageMSPSPM Master deviceS Slave deviceP Parked device (inactive)Wireless, Mobile Networks 6-6030
Bluetoothv v Originally by Japp Haartsen and Sven Mattison of Ericsson in 1994Replacement for RS-232 cables§ Short-range ( 1m to 100m)§ Low data rate BT 1.x 1Mbps – GFSKBT 2.x (EDR) 3Mbps – GFSK PSKBT 3.0 (AMP) – 802.11 ratesBT 4.0 (LE)§ Low power ( 40mA/0.2mA)v v Connects multiple devicesBluetooth Special Interest Group (SIG)§ 1998 – started with 5 companies Ericsson, Nokia, IBM, Toshiba, Intel§ Now – over 10,000Bluetooth31
Bluetooth 1.0 PHY2.4 GHz ISM bandv Modulation – GFSKv Frequency hoppingv § Over 79 1MHz carriers world-wide (except for France,Spain and Japan – 23 carriers)§ 1600/sec (dwell time 625μs)v Long repetition interval of frequency-hopsequence§ Over 23 hoursPiconet – Basic TopologyStar shapev 1 master node controls up to 7active slave nodesv § And controls up to 255 parkednodes (in energy save mode)v All nodes follow the samehopping sequence as the master32
Links in Piconet – TDD/TDMAv SCO – synchronous connection oriented§ Period negotiated with master§ Supports symmetric, circuit-switched connections§ Usually for voicev ACL – asynchronous connectionless§ Master polls each slave§ Slave responds immediately§ Response can take 1, 3, or 5 slotsScatternetv Piconets interconnected§ Slave in multiple piconets§ Master also a slaveNodes in the same piconethop with the masterv Inter-piconet communicationnot specified in specificationv 33
IEEE 802.15.3 – UWBHigh data rate WPANv UWBv Motivation: The need for higher bandwidths thancurrently supported by 802.15.1v § 100 Mpbs within 10 meter§ 400 Mpbs within 5 meterData, High quality TV, Home cinemav Wireless USBv IEEE 802.15.4 & ZigBeev Short range§ 30mv Low rate§ 250kbpsv Low power consumption§ Attractive for sensor networkingv PHY34
IEEE 802.15.4 & ZigBee (cont’d)v Types of devices§ Reduced Function Devices (RFDs)§ Full Function Devices (FFDs)v Roles of a devices in the network§ Network coordinator§ Router§ End-devicev Topologies§ Star§ Tree§ MeshSelected ComparisonsStandardBandwidth PowerProtocolStrongholdstack sizeApplicationsWi-Fi 54Mbps400mA TX20mA ST100 KBData rateInternet, PCnetworkingBluetooth 1Mbps40mA TX0.2mA ST 100KBInteroperability CableZigBee 250kbps 30mA TX34KB.356mA STreplacement:wireless USB &headsetLow powerSensornetworks,remotecontrol35
IEEE 802.16 WiMAXBroadband MANv IEEE 802.16v § Wireless last-mile alternative§ stationary subscribers, e.g. transceivers mounted ontop of business or residential buildings§ 2-10GHz§ Supports thousands of users simultaneously§ TDMA OFDM / OFDMAv IEEE 802.16e§ Support low speed mobile usersIEEE 802.20 Mobile Broadbandv Supports mobile users at very high speed§ 250 km/hrOperates in licensed 500MHz 3.5GHz bandv Data rate 1Mbpsv 36
What is mobility?v spectrum of mobility, from the network perspective:no mobilitymobile wireless user,using same accesspointhigh mobilitymobile user,connecting/disconnecting fromnetwork usingDHCP.mobile user, passingthrough multipleaccess point whilemaintaining ongoingconnections (like cellphone)Wireless, Mobile Networks 6-73Mobility: vocabularyhome network: permanent“home” of mobile(e.g., 128.119.40/24)home agent: entity that willperform mobility functions onbehalf of mobile, when mobile isremotewide areanetworkpermanent address:address in homenetwork, can always beused to reach mobilee.g., 128.119.40.186Wireless, Mobile Networks 6-7437
Mobility: more vocabularypermanent address: remainsconstant (e.g., 128.119.40.186)visited network: network inwhich mobile currentlyresides (e.g., 79.129.13/24)care-of-address: addressin visited network.(e.g., 79,129.13.2)wide areanetworkcorrespondent: wantsto communicate withmobileforeign agent: entity invisited network thatperforms mobilityfunctions on behalf ofmobile.Wireless, Mobile Networks 6-75How do you contact a mobile friend:Consider friend frequently changingaddresses, how do you find her?v v v I wonder whereAlice moved to?search all phone books?call her parents?expect her to let youknow where he/she is?Wireless, Mobile Networks 6-7638
Mobility: approachesv v let routing handle it: routers advertise permanent address ofmobile-nodes-in-residence via usual routing table exchange.§ routing tables indicate where each mobile located§ no changes to end-systemslet end-systems handle it:§ indirect routing: communication from correspondent tomobile goes through home agent, then forwarded toremote§ direct routing: correspondent gets foreign address ofmobile, sends directly to mobileWireless, Mobile Networks 6-77Mobility: approachesv v let routing handle it: routers advertise permanent address ofnot via usual routing table exchange.mobile-nodes-in-residencescalable§ routing tables indicatewhere each mobile locatedto millions of§ no changes to end-systemsmobileslet end-systems handle it:§ indirect routing: communication from correspondent tomobile goes through home agent, then forwarded toremote§ direct routing: correspondent gets foreign address ofmobile, sends directly to mobileWireless, Mobile Networks 6-7839
Mobility: registrationvisited networkhome network12 areawidenetworkmobile contactsforeign agent onentering visitednetworkforeign agent contacts homeagent home: “this mobile isresident in my network”end result:v foreign agent knows about mobilev home agent knows location of mobileWireless, Mobile Networks 6-79Mobility via indirect routinghome agent interceptspackets, forwards toforeign agentforeign agentreceives packets,forwards to mobilehomenetwork31correspondentaddresses packetsusing home address ofmobilevisitednetworkwide areanetwork24mobile repliesdirectly tocorrespondentWireless, Mobile Networks 6-8040
Indirect Routing: commentsv mobile uses two addresses:§ permanent address: used by correspondent (hencemobile location is transparent to correspondent)§ care-of-address: used by home agent to forwarddatagrams to mobileforeign agent functions may be done by mobile itselfv triangle routing: correspondent-home-networkmobilev § inefficient whencorrespondent, mobileare in same networkWireless, Mobile Networks 6-81Indirect routing: moving between networkssuppose 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 (butwith new care-of-address)v mobility, changing foreign networks transparent: ongoing connections can be maintained!v Wireless, Mobile Networks 6-8241
Mobility via direct routingforeign agentreceives packets,forwards to mobilecorrespondent forwardsto foreign agentvisitednetworkhomenetwork3214mobile repliesdirectly tocorrespondentcorrespondentrequests, receivesforeign address ofmobileWireless, Mobile Networks 6-83Mobility via direct routing: commentsovercome triangle routing problemv non-transparent to correspondent: correspondentmust get care-of-address from home agentv § what if mobile changes visited network?1324Wireless, Mobile Networks 6-8442
Accommodating mobility with direct routinganchor foreign agent: FA in first visited networkv data always routed first to anchor FAv when mobile moves: new FA arranges to havedata forwarded from old FA (chaining)v foreign net visitedat session startwide respondentagentnew foreignagentnewforeignnetworkWireless, Mobile Networks 6-85Mobile IPRFC 3344v has many features we’ve seen:v § home agents, foreign agents, foreign-agent registration,care-of-addresses, encapsulation (packet-within-apacket)v three components to standard:§ indirect routing of datagrams§ agent discovery§ registration with home agentWireless, Mobile Networks 6-8643
Mobile IP: indirect routingforeign-agent-to-mobile packetpacket sent by home agent to foreignagent: a packet within a packetdest: 79.129.13.2dest: 128.119.40.186dest: 128.119.40.186Permanent address:128.119.40.186dest: 128.119.40.186Care-of address:79.129.13.2packet sent bycorrespondentWireless, Mobile Networks 6-87Mobile IP: agent discoveryv agent advertisement: foreign/home agents advertiseservice by broadcasting ICMP messages (typefield 9)H,F bits: home and/orforeign agentR bit: registrationrequiredWireless, Mobile Networks 6-8844
Mobile IP: registration examplehome agentHA: 128.119.40.7visited network: 79.129.13/24foreign agentCOA: 79.129.13.2ICMP agent adv.mobile agentMA: 128.119.40.186COA: 79.129.13.2 .registration req.COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186Lifetime: 9999identification: 714encapsulation format .registration replyHA: 128.119.40.7MA: 128.119.40.186Lifetime: 4999Identification: 714encapsulation format .registration req.COA: 79.129.13.2HA: 128.119.40.7MA: 128.119.40.186Lifetime: 9999identification:714 .registration replyHA: 128.119.40.7MA: 128.119.40.186Lifetime: 4999Identification: 714 .timeWireless, Mobile Networks 6-89Wireless, mobility: impact on higher layer protocolsv logically, impact 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 handoff§ TCP interprets loss as congestion, will decrease congestionwindow un-necessarily§ delay impairments for real-time traffic§ limited bandwidth of wireless linksWireless, Mobile Networks 6-9045
Wireless, Mobile Networks 6-3 Elements of a wireless network network infrastructure Wireless, Mobile Networks 6-4 . CDMA, GSM 2.5G: UMTS/WCDMA, CDMA2000 802.11a,g 3G: UMTS/WCDMA-HSPDA, CDMA2000-1xEVDO 4G: LTWE WIMAX 802.11a,g point-to-point 200 802.11n s) Wireless, Mobile Networks 6-8 infrastructure mode !
Part One: Heir of Ash Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26 Chapter 27 Chapter 28 Chapter 29 Chapter 30 .
TO KILL A MOCKINGBIRD. Contents Dedication Epigraph Part One Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 Part Two Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18. Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 Chapter 24 Chapter 25 Chapter 26
DEDICATION PART ONE Chapter 1 Chapter 2 Chapter 3 Chapter 4 Chapter 5 Chapter 6 Chapter 7 Chapter 8 Chapter 9 Chapter 10 Chapter 11 PART TWO Chapter 12 Chapter 13 Chapter 14 Chapter 15 Chapter 16 Chapter 17 Chapter 18 Chapter 19 Chapter 20 Chapter 21 Chapter 22 Chapter 23 .
Mobile 3G/4G, pushing wireless boundaries to enable the best mobile experiences 2 Mobile connectivity is an amazing technical achievement, 4 critical to the mobile experience Wireless fundamentals are the foundation to mobile powered by Mobile 3G/4G technologies Appreciating the magic of mobile requires un
Wireless# Guide to Wireless Communications Chapter 1 Introduction to Wireless Communications . Wireless Local Area Network (WLAN) - Extension of a wired LAN Connecting to it through a device called a wireless . network Each computer on the WLAN has a wireless network interface card (NIC) - With an antenna built into it .
About the husband’s secret. Dedication Epigraph Pandora Monday Chapter One Chapter Two Chapter Three Chapter Four Chapter Five Tuesday Chapter Six Chapter Seven. Chapter Eight Chapter Nine Chapter Ten Chapter Eleven Chapter Twelve Chapter Thirteen Chapter Fourteen Chapter Fifteen Chapter Sixteen Chapter Seventeen Chapter Eighteen
18.4 35 18.5 35 I Solutions to Applying the Concepts Questions II Answers to End-of-chapter Conceptual Questions Chapter 1 37 Chapter 2 38 Chapter 3 39 Chapter 4 40 Chapter 5 43 Chapter 6 45 Chapter 7 46 Chapter 8 47 Chapter 9 50 Chapter 10 52 Chapter 11 55 Chapter 12 56 Chapter 13 57 Chapter 14 61 Chapter 15 62 Chapter 16 63 Chapter 17 65 .
Your sheet-pile program FADSPABW (B-9) is a special case of this method. It was separately written, although several subroutines are the same, because there are special features involved in sheet-pile design. These additional considerations would in-troduce unnecessary complexity into a program for lateral piles so that it would be a little more difficult to use. Many consider it difficult in .
