Chapter6

nullnull6: Wireless and Mobile Networks6-*Chapter 6 Wireless 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 lot of 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/KWR All material copyright 1996-2009 J.F Kurose and K.W. Ross, All Rights ReservedComputer Networking: A Top Down Approach 5th edition. Jim Kurose, Keith Ross Addison-Wesley, April 2009. Chapter 6: Wireless and Mobile Networks6: Wireless and Mobile Networks6-*Chapter 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 networkChapter 6 outline6: Wireless and Mobile Networks6-*Chapter 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 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higher-layer protocols 6.9 SummaryElements of a wireless network6: Wireless and Mobile Networks6-*Elements of a wireless networkElements of a wireless network6: Wireless and Mobile Networks6-*Elements of a wireless networkElements of a wireless network6: Wireless and Mobile Networks6-*Elements of a wireless network wireless 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 distanceCharacteristics of selected wireless link standards6: Wireless and Mobile Networks6-*Characteristics of selected wireless link standardsIndoor 10-30mOutdoor 50-200mMid-range outdoor 200m – 4 KmLong-range outdoor 5Km – 20 Km.056.384145-1154IS-95, CDMA, GSM2GUMTS/WCDMA, CDMA20003G802.15802.11b802.11a,gUMTS/WCDMA-HSPDA, CDMA2000-1xEVDO3G cellular enhanced802.16 (WiMAX)802.11a,g point-to-point200802.11nData rate (Mbps)dataElements of a wireless network6: Wireless and Mobile Networks6-*Elements of a wireless networkElements of a wireless network6: Wireless and Mobile Networks6-*Elements 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 themselvesWireless network taxonomy6: Wireless and Mobile Networks6-*Wireless network taxonomysingle hopmultiple hopsinfrastructure (e.g., APs)no infrastructurehost connects to base station (WiFi, WiMAX, cellular) which connects to larger Internetno base station, no connection to larger Internet (Bluetooth, ad hoc nets)host may have to relay through several wireless nodes to connect to larger Internet: mesh netno base station, no connection to larger Internet. May have to relay to reach other a given wireless node MANET, VANETWireless Link Characteristics (1)6: Wireless and Mobile Networks6-*Wireless 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” Wireless Link Characteristics (2)6: Wireless and Mobile Networks6-*Wireless 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)BER10-110-210-310-510-610-710-4Wireless network characteristics6: Wireless and Mobile Networks6-*Wireless network characteristicsMultiple wireless senders and receivers create additional problems (beyond multiple access):Hidden terminal problem B, A hear each other B, C hear each other A, C can not hear each other means A, C unaware of their interference at B Signal attenuation: B, A hear each other B, C hear each other A, C can not hear each other interfering at BCode Division Multiple Access (CDMA)6: Wireless and Mobile Networks6-*Code 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”) CDMA Encode/Decode6: Wireless and Mobile Networks6-*CDMA Encode/Decodeslot 1slot 0Zi,m= di.cmslot 0 channel outputslot 1 channel outputchannel output Zi,msendercodedata bitsslot 1slot 0slot 0 channel outputslot 1 channel outputreceivercodereceived inputCDMA: two-sender interference6: Wireless and Mobile Networks6-*CDMA: two-sender interferenceChapter 6 outline6: Wireless and Mobile Networks6-*Chapter 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 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higher-layer protocols 6.9 SummaryIEEE 802.11 Wireless LAN6: Wireless and Mobile Networks6-*IEEE 802.11 Wireless LAN802.11b 2.4-5 GHz unlicensed spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code802.11a 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 Mbpsall use CSMA/CA for multiple access all have base-station and ad-hoc network versions802.11 LAN architecture6: Wireless and Mobile Networks6-*802.11 LAN architecturewireless 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 2hub, switch or router802.11: Channels, association6: Wireless and Mobile Networks6-*802.11: Channels, association802.11b: 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 associate with an AP scans channels, listening for beacon frames containing 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 subnet 802.11: passive/active scanning6: Wireless and Mobile Networks6-*802.11: passive/active scanningAP 2AP 1H1BBS 2BBS 1Active Scanning: Probe Request frame broadcast from H1 Probes response frame sent from APs Association Request frame sent: H1 to selected AP Association Response frame sent: H1 to selected APAP 2AP 1H1BBS 2BBS 1Passive Scanning: beacon frames sent from APs association Request frame sent: H1 to selected AP association Response frame sent: H1 to selected APIEEE 802.11: multiple access6: Wireless and Mobile Networks6-*IEEE 802.11: multiple accessavoid collisions: 2+ nodes transmitting at same time 802.11: CSMA - sense before transmitting don’t collide with ongoing transmission by other node 802.11: no collision 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)IEEE 802.11 MAC Protocol: CSMA/CA6: Wireless and Mobile Networks6-*IEEE 802.11 MAC Protocol: CSMA/CA802.11 sender 1 if sense channel idle for DIFS then transmit entire frame (no CD) 2 if sense channel busy then start random backoff time timer counts down while channel idle transmit when timer expires if no ACK, increase random backoff interval, repeat 2 802.11 receiver - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) senderreceiverAvoiding collisions (more)6: Wireless and Mobile Networks6-*Avoiding collisions (more)idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames sender first transmits small request-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 CTS heard by all nodes sender transmits data frame other stations defer transmissions avoid data frame collisions completely using small reservation packets!Collision Avoidance: RTS-CTS exchange6: Wireless and Mobile Networks6-*Collision Avoidance: RTS-CTS exchangeAPABtimedefer802.11 frame: addressing6: Wireless and Mobile Networks6-*802.11 frame: addressingAddress 2: MAC address of wireless host or AP transmitting this frameAddress 1: MAC address of wireless host or AP to receive this frameAddress 3: MAC address of router interface to which AP is attachedAddress 4: used only in ad hoc modenull6: Wireless and Mobile Networks6-*H1R1802.11 frame: addressingnull6: Wireless and Mobile Networks6-*802.11 frame: moreduration of reserved transmission time (RTS/CTS)frame seq # (for RDT)frame type (RTS, CTS, ACK, data)null6: Wireless and Mobile Networks6-*hub or switchAP 2AP 1H1BBS 2BBS 1802.11: mobility within same subnetH1 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 H1null6: Wireless and Mobile Networks6-*802.11: 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 BERnull6: Wireless and Mobile Networks6-*802.11: 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 frame null6: Wireless and Mobile Networks6-*radius of coverage802.15: personal area networkless 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 kbps null6: Wireless and Mobile Networks6-*802.16: WiMAXlike 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 Mbps point-to-multipointpoint-to-pointnull6: Wireless and Mobile Networks6-*802.16: WiMAX: downlink, uplink schedulingtransmission frame down-link subframe: base station to node uplink subframe: node to base stationbase station tells nodes who will get to receive (DL map) and who will get to send (UL map), and whenWiMAX standard provide mechanism for scheduling, but not scheduling algorithmChapter 6 outline6: Wireless and Mobile Networks6-*Chapter 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 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higher-layer protocols 6.9 Summarynull6: Wireless and Mobile Networks6-*Components of cellular network architectureCellular networks: the first hop6: Wireless and Mobile Networks6-*Cellular 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 accessCellular standards: brief survey6: Wireless and Mobile Networks6-*Cellular 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 bowl of alphabet soup: use this for reference onlyCellular standards: brief survey6: Wireless and Mobile Networks6-*Cellular 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-95 Cellular standards: brief survey6: Wireless and Mobile Networks6-*Cellular 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: 1xEvolution Data Optimized (1xEVDO) up to 14 Mbps ….. more (and more interesting) cellular topics due to mobility (stay tuned for details)null6: Wireless and Mobile Networks6-*BSCBTSBase station system (BSS)Legend2G (voice) network architecture MSCPublic telephone networkGateway MSCGnull6: Wireless and Mobile Networks6-*2.5G (voice+data) network architectureBSCMSCSGSNPublic telephone networkGateway MSCGPublic InternetGGSNGKey insight: new cellular data network operates in parallel (except at edge) with existing cellular voice network voice network unchanged in core data network operates in parallel Chapter 6 outline6: Wireless and Mobile Networks6-*Chapter 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 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higher-layer protocols 6.9 SummaryWhat is mobility?6: Wireless and Mobile Networks6-*What is mobility?spectrum of mobility, from the network perspective:mobile 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. Mobility: Vocabulary6: Wireless and Mobile Networks6-*Mobility: Vocabularyhome network: permanent “home” of mobile (e.g., 128.119.40/24)Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remotewide area networkcorrespondentMobility: more vocabulary6: Wireless and Mobile Networks6-*Mobility: 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 mobileHow do you contact a mobile friend:6: Wireless and Mobile Networks6-*How do you contact 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?Mobility: approaches6: Wireless and Mobile Networks6-*Mobility: approachesLet 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 mobileMobility: approaches6: Wireless and Mobile Networks6-*Mobility: approachesLet 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 scalable to millions of mobilesMobility: registration6: Wireless and Mobile Networks6-*Mobility: registrationEnd result: Foreign agent knows about mobile Home agent knows location of mobilewide area networkhome networkvisited networkMobility via Indirect Routing6: Wireless and Mobile Networks6-*Mobility via Indirect Routingwide area networkhome networkvisited networkIndirect Routing: comments6: Wireless and Mobile Networks6-*Indirect Routing: commentsMobile 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 mobile foreign agent functions may be done by mobile itself triangle routing: correspondent-home-network-mobile inefficient when correspondent, mobile are in same networkIndirect Routing: moving between networks6: Wireless and Mobile Networks6-*Indirect 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 (but with new care-of-address) mobility, changing foreign networks transparent: on going connections can be maintained!Mobility via Direct Routing6: Wireless and Mobile Networks6-*Mobility via Direct Routingwide area networkhome networkvisited networkcorrespondent requests, receives foreign address of mobilecorrespondent forwards to foreign agentMobility via Direct Routing: comments6: Wireless and Mobile Networks6-*Mobility via Direct Routing: commentsovercome triangle routing problem non-transparent to correspondent: correspondent must get care-of-address from home agent what if mobile changes visited network?Accommodating mobility with direct routing6: Wireless and