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802.11 Wireless and Mobile IP

802.11 Wireless and Mobile IP. Wireless and 802.11 LANs wireless links: shared, fading, interference, hidden terminal problem IEEE 802.11 ( “ wi-fi ” ) CSMA/CA reflects wireless channel characteristics DIFS, SIFS, receiver ACK, RTS/CTS, NAV, … Mobility

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802.11 Wireless and Mobile IP

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  1. 802.11 Wireless and Mobile IP Wireless and 802.11 LANs • wireless links: • shared, fading, interference, hidden terminal problem • IEEE 802.11 (“wi-fi”) • CSMA/CA reflects wireless channel characteristics • DIFS, SIFS, receiver ACK, RTS/CTS, NAV, … Mobility • principles: addressing, routing to mobile users • home, visited networks • direct, indirect routing • care-of-addresses • case studies (optional) • mobile IP Overview of cellular network architectures & evolution (optional) Readings: Textbook, Chapter 6, Sections 6.2-6.3, and Sections 6.5-6.6, 6.8 CSci4211 802.11 Wireless and Mobile IP

  2. Background: # 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 communication over wireless link handling mobile user who changes point of attachment to network Chapter 6: Wireless and Mobile Networks CSci4211 802.11 Wireless and Mobile IP

  3. 6.1 Introduction Wireless 6.2 Wireless links, characteristics CDMA 6.3 IEEE 802.11 wireless LANs (“wi-fi”) 6.4Cellular Internet Access architecture standards (e.g., GSM) Mobility 6.5 Principles: addressing and routing to mobile users 6.6 Mobile IP 6.7 Handling mobility in cellular networks 6.8 Mobility and higher-layer protocols 6.9Summary Chapter 6 outline CSci4211 802.11 Wireless and Mobile IP

  4. wireless hosts • laptop, PDA, IP phone • run applications • may be stationary (non-mobile) or mobile • wireless does not always mean mobility network infrastructure Elements of a Wireless Network CSci4211 802.11 Wireless and Mobile IP

  5. base station • typically connected to wired network • relay - responsible for sending packets between wired network and wireless host(s) in its “area” • e.g., cell towers 802.11 access points network infrastructure Elements of a Wireless Network CSci4211 802.11 Wireless and Mobile IP

  6. network infrastructure 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 distance CSci4211 802.11 Wireless and Mobile IP

  7. Wireless Link Characteristics 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” CSci4211 802.11 Wireless and Mobile IP

  8. Outdoor 50 – 200m Mid range outdoor 200m – 4Km Long range outdoor 5Km – 20Km Indoor 10 – 30m Characteristics of Selected Wireless Link Standards 54 Mbps 802.11{a,g} 5-11 Mbps .11 p-to-p link 802.11b 1 Mbps 802.15 3G 384 Kbps UMTS/WCDMA, CDMA2000 2G 56 Kbps IS-95 CDMA, GSM CSci4211 802.11 Wireless and Mobile IP

  9. infrastructure mode • base station connects mobiles into wired network • handoff: mobile changes base station providing connection into wired network network infrastructure Elements of a Wireless Network CSci4211 802.11 Wireless and Mobile IP

  10. Elements of a Wireless Network • Ad hoc mode • no base stations • nodes can only transmit to other nodes within link coverage • nodes organize themselves into a network: route among themselves CSci4211 802.11 Wireless and Mobile IP

  11. 802.11b 2.4-5 GHz unlicensed radio spectrum up to 11 Mbps direct sequence spread spectrum (DSSS) in physical layer all hosts use same chipping code widely deployed, using base stations 802.11a 5-6 GHz range up to 54 Mbps 802.11g 2.4-5 GHz range up to 54 Mbps 802.11n MIMO, 20/40MHz channels in 2.4 GHz up to 600 Mbps 802.11ac wider RF band per station (80/160 MHz), more MIMO, multi-user MIMO, 5 GHz at least 1 Gbpstotal, 500 Mbps per link All use CSMA/CA for multiple access All have base-station and ad-hoc network versions IEEE 802.11 Wireless LAN CSci4211 802.11 Wireless and Mobile IP

  12. AP AP Internet hub, switch or router BSS 1 BSS 2 802.11 LAN Infrastructure Mode • wireless host communicates with base station • base station = access point (AP) • Basic Service Set (BSS) (aka “cell”) in infrastructure mode contains: • wireless hosts • access point (AP): base station • ad hoc mode: hosts only CSci4211 802.11 Wireless and Mobile IP

  13. Ad Hoc Network Approach • No access point (i.e., base station) • “peer-to-peer” mode • wireless hosts communicate with each other • to get packet from wireless host A to B may need to route through wireless hosts X,Y,Z • Applications: • “laptop” meeting in conference room, car • interconnection of “personal” devices • battlefield • IETF MANET (Mobile Ad hoc Networks) working group CSci4211 802.11 Wireless and Mobile IP

  14. B A C C C’s signal strength A’s signal strength B A space Wireless Network Characteristics Multiple 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 fading: • B, A hear each other • B, C hear each other • A, C can not hear each other interferring at B CSci4211 802.11 Wireless and Mobile IP

  15. Hidden and Exposed Terminal Problems • Wireless networks: hidden and exposed nodes • A->B and C->B: A can’t hear C’s transmission • C hidden from A, can cause collision! • B->A and C->D: won’t interfere with each other, despite B can hear C’s transmission • C exposed to B, unnecessary backoff by B! CSci4211 802.11 Wireless and Mobile IP

  16. B A C C C’s signal strength A’s signal strength B A space IEEE 802.11: Multiple Access • avoid collisions: 2+ nodes transmitting at same time • 802.11: CSMA - sense before transmitting • don’t collide with ongoing transmission by other node • 802.11: no collision detection! • difficult to receive (sense collisions) when transmitting due to weak received signals (fading); • often need to switch between transmitting vs. receiving mode • can’t sense all collisions in any case: hidden terminal, fading • goal: avoid collisions: CSMA/C(ollision)A(voidance) CSci4211 802.11 Wireless and Mobile IP

  17. 802.11: Channels, Association • 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at different frequencies • AP admin chooses frequency for AP • interference possible: channel can be same as that chosen by neighboring AP! • host: must 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 CSci4211 802.11 Wireless and Mobile IP

  18. DIFS data SIFS ACK IEEE 802.11 MAC Protocol: CSMA/CA sender receiver 802.11 sender 1 if sense channel idle for DIFSthen transmit entire frame (no CD) 2 ifsense channel busy then start random backoff timer timer counts down while channel idle transmit when timer expires if no ACK (e.g., due to collision or bit error), increase random backoff interval, repeat 2 802.11 receiver - if frame received OK return ACK after SIFS (ACK needed due to hidden terminal problem) CSci4211 802.11 Wireless and Mobile IP

  19. Collision Avoidance Mechanisms • Problem: • two nodes, hidden from each other, transmit complete frames to base station • wasted bandwidth for long duration ! • Solution: • small reservation packets • nodes track reservation interval with internal “network allocation vector” (NAV) CSci4211 802.11 Wireless and Mobile IP

  20. Avoiding Collisions (cont’d) 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 • RTS heard by all nodes • sender transmits data frame • other stations defer transmissions Avoid (large) data frame collisions using small reservation packets! CSci4211 802.11 Wireless and Mobile IP

  21. Collision Avoidance: Some Details • Sender transmits RequestToSend (RTS) frame • Receiver replies with ClearToSend (CTS) frame • Neighbors… • see CTS: keep quiet • see RTS but not CTS: ok to transmit • Receiver sends ACK when has frame • neighbors silent until see ACK • Collisions • no collisions detection • known when don’t receive CTS • exponential backoff CSci4211 802.11 Wireless and Mobile IP

  22. Collision Avoidance: RTS-CTS Exchange • sender transmits short RTS (request to send) packet: indicates duration of transmission • receiver replies with short CTS (clear to send) packet • notifying (possibly hidden) nodes • hidden nodes will not transmit for specified duration: NAV CSci4211 802.11 Wireless and Mobile IP

  23. RTS(B) RTS(A) reservation collision RTS(A) CTS(A) CTS(A) DATA (A) ACK(A) ACK(A) Collision Avoidance: RTS-CTS Exchange B A AP defer time CSci4211 802.11 Wireless and Mobile IP

  24. 6 4 2 2 6 6 6 2 0 - 2312 frame control duration address 1 address 2 address 3 address 4 payload CRC seq control 802.11 Frame: Addressing Address 4: used when frames are forwarded from one AP to another AP (MAC address of actual source) Address 1: MAC address of wireless host or AP to receive this frame Address 3: MAC address of original (i.e., actual!) source or destination when frames are forwarded by AP Address 2: MAC address of wireless host or AP transmitting this frame CSci4211 802.11 Wireless and Mobile IP

  25. router AP Internet R1 MAC addr AP MAC addr source address dest. address 802.3frame AP MAC addr H1 MAC addr R1 MAC addr address 3 address 2 address 1 802.11 frame 802.11 Frame: Addressing H1 R1 CSci4211 802.11 Wireless and Mobile IP

  26. 6 4 2 2 6 6 6 2 0 - 2312 frame control duration address 1 address 2 address 3 address 4 payload CRC seq control 2 2 4 1 1 1 1 1 1 1 1 Protocol version Type Subtype To AP From AP More frag Retry Power mgt More data WEP Rsvd 802.11 Frame: More frame seq # (for reliable ARQ) duration of reserved transmission time (RTS/CTS) frame type (RTS, CTS, ACK, data) CSci4211 802.11 Wireless and Mobile IP

  27. H1 remains in same IP subnet: IP address can remain same switch: which AP is associated with H1? self-learning (Ch. 5): switch will see frame from H1 and “remember” which switch port can be used to reach H1 router 802.11: Mobility within Same Subnet hub or switch BBS 1 AP 1 AP 2 H1 BBS 2 CSci4211 802.11 Wireless and Mobile IP

  28. Mobility with a Subnet(cont’d) • Scanning (selecting an AP) • node sends Probe frame • all AP’s w/in reach reply with ProbeResponse frame • node selects one AP; sends it AssociateRequest frame • AP replies with AssociationResponse frame • new AP informs old AP via tethered network • When • active: when join or move • passive: AP periodically sends Beacon frame CSci4211 802.11 Wireless and Mobile IP

  29. Low-power, small radius, wireless networking technology 10-100 meters omnidirectional not line-of-sight infrared Interconnects gadgets 2.4-2.5 GHz unlicensed radio band up to 721 kbps Interference from wireless LANs, digital cordless phones, microwave ovens: frequency hopping helps MAC protocol supports: error correction ARQ Each node has a 12-bit address A Word about Bluetooth CSci4211 802.11 Wireless and Mobile IP

  30. P P P P P M M Master device Slave device Parked device (inactive) S S S S 802.15: Personal Area Network • less than 10 m diameter • replacement for cables (mouse, keyboard, headphones) • ad hoc: no infrastructure • master/slaves: • slaves request permission to send (to master) • master grants requests • 802.15: evolved from Bluetooth specification • 2.4-2.5 GHz radio band • up to 721 kbps radius of coverage CSci4211 802.11 Wireless and Mobile IP

  31. no mobility high mobility (Wide-Area) Mobility (optional) • What is mobility? • spectrum of mobility, from thenetwork perspective: mobile wireless user, using same access point mobile user, passing through multiple access point while maintaining ongoing connections (like cell phone) mobile user, connecting/ disconnecting from network using DHCP. CSci4211 802.11 Wireless and Mobile IP

  32. Mobility: Vocabulary home network: permanent “home” of mobile (e.g., 128.119.40/24) home agent: entity that will perform mobility functions on behalf of mobile, when mobile is remote wide area network Permanent address: address in home network, can always be used to reach mobile e.g., 128.119.40.186 correspondent CSci4211 802.11 Wireless and Mobile IP

  33. Mobility: More Vocabulary visited network: network in which mobile currently resides (e.g., 79.129.13/24) Permanent address: remains constant (e.g., 128.119.40.186) Care-of-address: address in visited network. (e.g., 79,129.13.2) wide area network foreign agent: entity in visited network that performs mobility functions on behalf of mobile. correspondent: wants to communicate with mobile CSci4211 802.11 Wireless and Mobile IP

  34. How do you contact a mobile friend: I wonder where Alice moved to? Consider friend frequently changing addresses, how do you find her? • search all phone books? • call her parents? • expect her to let you know where he/she is? CSci4211 802.11 Wireless and Mobile IP

  35. Mobility: Approaches • Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. • routing tables indicate where each mobile located • no changes to end-systems • Let end-systems handle it: • indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote • direct routing: correspondent gets foreign address of mobile, sends directly to mobile CSci4211 802.11 Wireless and Mobile IP

  36. Mobility: Approaches not scalable to millions of mobiles • Let routing handle it: routers advertise permanent address of mobile-nodes-in-residence via usual routing table exchange. • routing tables indicate where each mobile located • no changes to end-systems • let end-systems handle it: • indirect routing: communication from correspondent to mobile goes through home agent, then forwarded to remote • direct routing: correspondent gets foreign address of mobile, sends directly to mobile CSci4211 802.11 Wireless and Mobile IP

  37. mobile contacts foreign agent on entering visited network foreign agent contacts home agent home: “this mobile is resident in my network” 1 2 Mobility: Registration visited network home network End result: • Foreign agent knows about mobile • Home agent knows location of mobile wide area network CSci4211 802.11 Wireless and Mobile IP

  38. foreign agent receives packets, forwards to mobile home agent intercepts packets, forwards to foreign agent correspondent addresses packets using home address of mobile mobile replies directly to correspondent 3 2 4 1 Mobility via Indirect Routing visited network home network wide area network CSci4211 802.11 Wireless and Mobile IP

  39. Indirect Routing: Comments • Mobile 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 network CSci4211 802.11 Wireless and Mobile IP

  40. Indirect Routing: Moving between Networks • suppose mobile user moves to another network • registers with new foreign agent • new foreign agent registers with home agent • home agent update care-of-address for mobile • packets continue to be forwarded to mobile (but with new care-of-address) • mobility, changing foreign networks transparent: on going connections can be maintained! CSci4211 802.11 Wireless and Mobile IP

  41. foreign agent receives packets, forwards to mobile mobile replies directly to correspondent 4 2 4 1 3 Mobility via Direct Routing correspondent forwards to foreign agent visited network home network wide area network correspondent requests, receives foreign address of mobile CSci4211 802.11 Wireless and Mobile IP

  42. Mobility via Direct Routing: Comments • overcome triangle routing problem • non-transparent to correspondent: correspondent must get care-of-address from home agent • what if mobile changes visited network? CSci4211 802.11 Wireless and Mobile IP

  43. 1 2 4 3 5 Accommodating Mobility w/ Direct Routing • anchor foreign agent: FA in first visited network • data always routed first to anchor FA • when mobile moves: new FA arranges to have data forwarded from old FA (chaining) foreign net visited at session start anchor foreign agent wide area network new foreign network correspondent agent correspondent new foreign agent CSci4211 802.11 Wireless and Mobile IP

  44. Mobile IP • RFC 3220 • has many features we’ve seen: • home agents, foreign agents, foreign-agent registration, care-of-addresses, encapsulation (packet-within-a-packet) • three components to standard: • indirect routing of datagrams • agent discovery • registration with home agent CSci4211 802.11 Wireless and Mobile IP

  45. foreign-agent-to-mobile packet packet sent by home agent to foreign agent: a packet within a packet dest: 128.119.40.186 dest: 128.119.40.186 dest: 128.119.40.186 packet sent by correspondent dest: 79.129.13.2 Mobile IP: Indirect Routing Permanent address: 128.119.40.186 Care-of address: 79.129.13.2 CSci4211 802.11 Wireless and Mobile IP

  46. Mobile IP: Agent Discovery • agent advertisement: foreign/home agents advertise service by broadcasting ICMP messages (typefield = 9) H,F bits: home and/or foreign agent R bit: registration required CSci4211 802.11 Wireless and Mobile IP

  47. Mobile IP: Registration Example CSci4211 802.11 Wireless and Mobile IP

  48. Wireless, Mobility: Impact on Higher Layer Protocols • logically, impact should be minimal … • best effort service model remains unchanged • TCP and UDP can (and do) run over wireless, mobile • … but performance-wise: • packet loss/delay due to bit-errors (discarded packets, delays for link-layer retransmissions), and handoff • TCP interprets loss as congestion, will decrease congestion window un-necessarily • delay impairments for real-time traffic • limited bandwidth of wireless links CSci4211 802.11 Wireless and Mobile IP

  49. Cellular Voice/Data Architectures:A Primer [Optional Material] • Basics of Cellular Networks • Survey of 2G/3G Cellular Network Standards • 2G • 2.5G • 3G • 3.5G • 2.5G/3G Voice/Data Network Architectures • 4G LTE/LTE Advanced Network Architectures CSci4211 802.11 Wireless and Mobile IP

  50. connects cells to wide area net • manages call setup • handles mobility Mobile Switching Center Mobile Switching Center • covers geographical region • base station (BS) analogous to 802.11 AP • mobile users attach to network through BS • air-interface: physical and link layer protocol between mobile and BS Public telephone network, and Internet MSC cell wired network Cellular Network Architecture: basic terminology & components CSci4211 802.11 Wireless and Mobile IP

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