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Ch 6. Wireless LANs

Ch 6. Wireless LANs. Myungchul Kim mckim@icu.ac.kr. SESSION: Wireless LANs. Wireless LAN Overview Wireless Network Technologies (infrared, spread spectrum, microwave) IEEE 802.11 Overview 802 MAC 802 Physical Layer Mobile Adhoc Networks. Wireless LANs.

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Ch 6. Wireless LANs

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  1. Ch 6. Wireless LANs Myungchul Kim mckim@icu.ac.kr

  2. SESSION: Wireless LANs Wireless LAN Overview Wireless Network Technologies (infrared, spread spectrum, microwave) IEEE 802.11 Overview 802 MAC 802 Physical Layer Mobile Adhoc Networks

  3. Wireless LANs • First generation of products at about 1-2 Mbps • Lucent’s WaveLAN, RadioLAN, etc. • factor of 10 less bandwidth than current Ethernet • Next generation of products at 10-11 Mbps • factor of 10 less bandwidth than 100 Mbps Ethernet • IEEE 802.11 standard • Important niche and enterprise applications (e.g. hospitals) • Increasing horizontal market interest • Forecast: Total worldwide wireless LAN market revenues: $305.4M (1998) to $1.63B by 2005 -- Frost & Sullivan.

  4. Wireless LANs Wired LAN Wireless LAN (Cell size 10 Meters to 100 Meters) Access Point

  5. Wireless LAN Applications • LAN Extension: Wireless LAN linked into a wired LAN on same premises • Wired LAN for Backbone • Wireless LAN (Stations in large open areas) • Cross-building interconnect: Connect LANs in nearby buildings • Point-to-point wireless (Devices connected are typically bridges or routers) • Nomadic Access: Wireless link between LAN hub and mobile data terminal equipped with antenna • Ad hoc networking: Temporary peer-to-peer network set up to meet immediate need • Example: link computers in a temporary network for duration of meeting

  6. Personal Area Network (PAN) Wireless LAN Configurations Access Point Wired LAN2 Wireless LAN1 (peer-to-peer) Wireless LAN-LAN Bridge Access Point as a repeater Wired LAN1 Wireless LAN2 (peer-to-peer) Wireless LAN3 (Master/slave) Access Point Wireless connection Wireless connection = Wireless LAN Adapter

  7. Wireless LAN Requirements • Throughput - more work completed per unit time • Number of nodes - hundreds across cells • Connection to backbone LAN - for corporate support • Service area - 100+ meters • Battery power consumption - sleep when not in use • Transmission robustness and security- reliable transmission, and maintain security • Collocated network operation - minimize interference between neighboring networks • License-free operation - better to operate without licensed frequencies • Handoff/roaming - MAC protocol should support smooth handoffs • Dynamic configuration - MAC addressing should support automatic addition and deletion of addresses

  8. OSI Stack LAN Stack LAN Stack OSI Layers 3-7 Upper Layers Logical Link Control (IEEE 802.2) OSI Layer 2 (Data Link) Media Access Control (MAC) IEEE802.3 Carrier Sense (Ethernet) IEEE802.4 Token Bus IEEE802.5 Token Ring IEEE802.11 Wireless OSI Layer 1 (Physical) Physical

  9. IEEE 802 Standards • 802.1: High Level Interface • 802.2: Logical Link Control • 802.3: CSMA/CD Networks • 802.4: Token Bus Networks • 802.5: Token Ring Networks • 802.6: Metropolitan Area Networks • 802.7: Broadband Networks • 802.8: Fiber Optic Networks • 802.9: Integrated Data and Voice Networks • 802.10 Virtual LANs • 802.11 Wireless LANs • 802.12 Communication media\ • 802.14 Data transport over traditional cable TV network • 802.15; personal area networks • 802.16 Wireless Local Loops

  10. Wireless LAN Technologies Access Point as a connector Wireless LAN Communication technologies • Infra red • Spread spectrum • Narrowband Wired LAN Access Point as a repeater Wireless LAN Communication technologies • Infra red • Spread spectrum • Narrowband Wireless connection Wireless connection = Wireless LAN Adapter

  11. Roaming support Wireless LAN Cell Wireless LAN Cell Y Z X, Y, Z are access points for the wireless LANs Handoffs and roaming is accomplished through access points (not very smooth) Wireless LAN Cell X

  12. Centrex A Sample Wireless School Link to Public Ethernet C D T1 or DSL LAN Server Wireless LAN Cell Wireless LAN Cell Z Y Router Wired Ethernet LAN • X, Y, Z are • access points • for the wireless • Ethernet LANs Wireless LAN Cell X • A, B, C, D are • student laptops A B

  13. IEEE 802.11 Upper Layers Upper Layers IEEE 802.2 Logical Link Control IEEE 802.2 Logical Link Control MAC Layer _______ Physical Layer IEEE 802.11 Wireless IEEE 802.11 Wireless Local Bridge (Access Point)

  14. Wireless LAN Categories • Spread spectrum LANs • Infrared (IR) LANs • Narrowband microwave • Carrier current LANs (psuedo wireless LANs) • Does not require installation of network cables • Uses power cables and a powerline modem • Can be used to carry 1 to 2 Mbps data • Example: Radioshack Master Console to control coffee machine, lamps, heating systems

  15. Spread Spectrum LANs • Multiple-cell arrangement • Within a cell, either peer-to-peer or hub • Peer-to-peer topology: No hub • Access controlled with MAC algorithm (CSMA) • Appropriate for ad hoc LANs • Hub topology • Mounted on the ceiling, connected to backbone • May control access and/or multiport repeater • Automatic handoff of mobile stations • Stations in cell either: • Transmit to / receive from hub only • Broadcast using omnidirectional antenna

  16. Infrared Over Microwave Radio Strengths: • Spectrum for infrared virtually unlimited • Possibility of high data rates • Infrared spectrum unregulated • Equipment inexpensive and simple • Reflected by light-colored objects • Ceiling reflection for entire room coverage • Doesn’t penetrate walls • More easily secured against eavesdropping • Less interference between different rooms Drawbacks: Indoor environments experience infrared background radiation • Sunlight and indoor lighting • Ambient radiation appears as noise • Transmitters of higher power required (safety)

  17. IR Data Transmission Techniques • Directed Beam Infrared • Used to create point-to-point links • Range depends on emitted power and degree of focusing • Focused IR data link can have range of kilometers • Cross-building interconnect between bridges or routers • Ominidirectional • Single base station in line of sight of all other stations on LAN • Station typically mounted on ceiling • Base station acts as a multiport repeater • Ceiling transmitter broadcasts signal received by IR transceivers • IR transceivers transmit with directional beam aimed at ceiling base unit • Diffused: All IR transmitters focused and aimed at a point on diffusely reflecting ceiling • IR radiation strikes ceiling: Reradiated omnidirectionally • Picked up by all receivers

  18. Narrowband Microwave LANs • Use of a microwave radio frequency band for signal transmission • Relatively narrow bandwidth • Licensed within specific geographic areas to avoid potential interference • Motorola - 600 licenses in 18-GHz range • Covers all metropolitan areas • Can assure that LANs in nearby locations don’t interfere • Encrypted transmissions prevent eavesdropping • Unlicensed: Uses unlicensed ISM spectrum • RadioLAN narrowband wireless LAN in 1995 • Low power (0.5 watts or less), Range = 50 m to 100 m • Operates at 10 Mbps in the 5.8-GHz band

  19. IEEE 802.11 Wireless LAN Standard

  20. General LAN Protocol Architecture • Functions of physical layer: • Encoding/decoding of signals • Preamble generation/removal (for synchronization) • Bit transmission/reception • Includes specification of the transmission medium • Functions of medium access control (MAC) layer: • On transmission, assemble data into a frame with address and error detection fields • On reception, disassemble frame and perform address recognition and error detection • Govern access to the LAN transmission medium • Functions of logical link control (LLC) Layer: • Provide an interface to higher layers and perform flow and error control

  21. IEEE 802.11 Architecture • Stations • Access point (AP) • Basic service set (BSS) • Stations competing for access to shared wireless medium • Isolated or connected to backbone DS through AP • Distribution system (DS) - interconnects several BSSs • Extended service set (ESS) • Two or more basic service sets interconnected by DS

  22. Centrex A Sample Wireless School -- IEEE 802.11 Terms Link to Public Ethernet Extended service set (ESS) C D T1 or DSL Wireless LAN Cell (BSS) LAN Server Wireless LAN Cell (BSS) Z Y Router Wired Ethernet LAN (DS) • X, Y, Z are • access points • for the wireless • Ethernet LANs Wireless LAN Cell (BSS) X • A, B, C, D are • laptops (Stations) A B

  23. Logical Link Control 802.11 Stack Contention-Free Service Contention Service Point Coordination Function (PCF) MAC Layer Distributed Coordination Function (DCF) 2.4 GHz frequency hopping spread spectrum 1 Mbps 2 Mbps 2.4 GHz direct sequence spread spectrum 1 Mbps 2 Mbps Infrared omni- directional 1 Mbps 2 Mbps 5-Ghz Orthogonal FDM 6,9,12 18,24,36, 48, 54 Mbps 2.4 GHz direct sequence spread spectrum 5.5 Mbps 11 Mbps 2.4 GHz Orthogonal FDM Up to 54 Mbps Physical Layer IEEE 802.11 IEEE 802.11a 802.11b 802.11g

  24. Physical Media Defined by Original 802.11 Standard • Direct-sequence spread spectrum • Operating in 2.4 GHz ISM band • Data rates of 1 and 2 Mbps • Frequency-hopping spread spectrum • Operating in 2.4 GHz ISM band • Data rates of 1 and 2 Mbps • Infrared • 1 and 2 Mbps • Wavelength between 850 and 950 nm

  25. IEEE 802.11 Family • IEEE 802.11a • Makes use of 5-GHz band • Provides rates of 6, 9 , 12, 18, 24, 36, 48, 54 Mbps • Uses orthogonal frequency division multiplexing (OFDM) • Subcarrier modulated using BPSK, QPSK, 16-QAM or 64-QAM • IEEE 802.11b • Makes use of 2.4-GHz band • Provides data rates of 5.5 and 11 Mbps • Uses Direct sequence Spread Spectrum • IEEE 802.11g • Makes use of 2.4-GHz band • Provides data rates of 54 Mbps an higher

  26. IEEE 802.11 Medium Access Control • MAC layer covers three functional areas: • Reliable data delivery • Access control • Security

  27. Reliable Data Delivery • MAC must handle interference, noise, fading, etc • More efficient to deal with errors at the MAC level than higher layer (such as TCP) • Frame exchange protocol • Source station transmits data • Destination responds with acknowledgment (ACK) • If source doesn’t receive ACK, it retransmits frame • Four frame exchange • Source issues request to send (RTS) • Destination responds with clear to send (CTS) • Source transmits data • Destination responds with ACK

  28. Access Control • Approaches proposed and accepted: • Distributed Coordination Function (required) • Uses Ethernet type CSMA • Useful in adhoc networks • Point Coordination Function (optional) • Implemented on top of DCF • Uses polling, typically done by an access point • Suitable for a centralized LAN

  29. Personal Area Network (PAN) Wireless LAN Configurations Access Point Wired LAN2 Wireless LAN1 (peer-to-peer) Wireless LAN-LAN Bridge Access Point as a repeater Wired LAN1 Wireless LAN2 (peer-to-peer) Wireless LAN3 (Master/slave) Access Point Wireless connection Wireless connection = Wireless LAN Adapter

  30. Interframe Space (IFS) DCF includes a set of delays (IFSs) with the following values: • Short IFS (SIFS) • Shortest IFS • Used for immediate response actions (high priority) • Point coordination function IFS (PIFS) • Midlength IFS • Used by centralized controller in PCF scheme when using polls • Distributed coordination function IFS (DIFS) • Longest IFS • Used as minimum delay for ordinary asynchronous frames contending for access • Extended IFS: Long period for errors

  31. MAC Frame Fields • Frame Control – frame type, control information • Duration/connection ID – channel allocation time • Addresses – context dependant, types include source and destination • Sequence control – numbering and reassembly • Frame body – MSDU or fragment of MSDU • Frame check sequence – 32-bit CRC

  32. Management Frames Used to manage communications between stations and Aps with subtypes (802.11 MIB): • Association request - from station to AP (includes security requirement) • Association response - AP to station • Reassociation request - station to AP when moved from one BSS, interactions with old AP • Reassociation response - AP to station • Probe request - locate a BSS (similar to ping) • Probe response - • Beacon - periodic signals to identify a BSS • Authentication - exchange of authentication frames • Deauthentication - terminate authentication

  33. Wired Equivalent Privacy Algorithm (WEP) • WEP intended to provide modest security for 802.11 LANs • Uses an encryption algorithm based on RC4 • Uses the following steps: • Integrity algorithm creates and appends a CRC • A pseudo random number generator (PRNG) is used to generate a ciphertext • Authentication in 802.11 • Open system authentication • Exchange of identities, no security benefits • Shared Secret Key authentication (secure)

  34. Access and Privacy Services As compared to wired LANs, wireless LANs must serve users not connected to the network Need special services: • Authentication • Establishes identity of stations to each other • Deathentication • Invoked when existing authentication is terminated • Privacy • Prevents message contents from being read by unintended recipient

  35. Mobile Adhoc Networks Overview • - Networks without any access points or fixed network infrastructure • Nodes “discover” each other when in vicinity and communicate • Bluetooth and wireless sensor networks are major examples

  36. HiperLAN Type 2 or HiperLAN2 Wireless LAN standard developed by the European Telecommunications Standards Institute (ETSI). • - Data rate of 54 Mbps • - High level of security • - QoS capabilities to support virtually any type of service or application • - High and scalable capacity as the number of users increase in the system

  37. Summary Wireless LAN Overview Wireless Network Technologies (infrared, spread spectrum, microwave) IEEE 802.11 Overview 802 MAC 802 Physical Layer MANETs

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