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Wireless Local Area Networks: Recent Developments

Ohio Highway Patrol. Wireless Local Area Networks: Recent Developments. Raj Jain The Ohio State University Columbus, OH 43210 http://www.cse.ohio-state.edu/~jain/. Overview. Spread Spectrum Wireless local area networks Wireless LAN standard: IEEE 802.11 Hiperlan Wireless ATM.

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Wireless Local Area Networks: Recent Developments

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  1. Ohio Highway Patrol Wireless Local Area Networks: Recent Developments Raj Jain The Ohio State UniversityColumbus, OH 43210http://www.cse.ohio-state.edu/~jain/

  2. Overview • Spread Spectrum • Wireless local area networks • Wireless LAN standard: IEEE 802.11 • Hiperlan • Wireless ATM

  3. Mobile vs Wireless • Mobile vs Stationary • Wireless vs Wired • Wireless media sharing issues • Mobile routing, addressing issues Mobile Wireless

  4. Frequency Hopping Spread Spectrum • Pseudo-random frequency hopping • Spreads the power over a wide spectrum Spread Spectrum • Developed initially for military • Patented by actress Hedy Lamarr (1942) • Narrowband interference can't jam Frequency 50 ms Time

  5. Spectrum Signal Noise Noise Signal (a) Normal (b) Frequency Hopping

  6. Direct-Sequence Spread Spectrum 0 1 • Spreading factor = Code bits/data bit, 10-100 commercial (Min 10 by FCC), 10,000 for military • Signal bandwidth >10 × data bandwidth • Code sequence synchronization • Correlation between codes InterferenceOrthogonal Data 0 1 0 0 1 0 1 1 0 1 1 0 1 1 0 1 0 0 1 0 Frequency 5s Time

  7. DS Spectrum Time Domain Frequency Domain Time Frequency (a) Data Frequency (b) Code

  8. Wireless LANs • IR Line of sight, short range, indoors • RF Need license • Spread-Spectrum: Resistance to interference Visible wave x-rays Infrared Ultraviolet 109 1010 1011 1012 1013 1014 1015 1016 1017 1018

  9. Wireless LANs Infrared Radio Line of Sight Diffuse Spread Spectrum Narrowband InfraLAN PhotonicsCollaborative Motorola ALTAIR 2.4 GHz 5.7GHz 902 GHz Proxim RangeLANNCR WaveLANTelesystems ArLAN DS DS FH FH Windata Freeport Proxim RangeLAN2

  10. Wireless LAN Products • Alps - Radioport • AT&T - WaveLAN • A.T. Schindler - FIRLAN • Carrier Communications - Carriernet • California Microwave - Radio Link • Digital (Compaq) - RoamAbout • IBM - Infrared wireless LAN Adapter • Digital Ocean - Grouper • InfraLAN Technologies - InfraLAN • Motorola - ALTAIR Plus II • O’Neill Communications - LAWN

  11. WLAN Products (Cont.) • Photonics - Collaborate Series • Proxim- RangeLAN2 • Solectek - AirLAN • Spectrix - SpectrixLite • TELXON - ARLAN 600 • Travelling Software - Airshare • WiLAN - 902-20 • Windata - FreePort • Xerox - PARCTAB • Xircom - NetWave

  12. IEEE 802.11 Features • 1 and 2 Mbps • Supports both Ad-hoc and base-stations • Supports multiple priorities • Supports time-critical and data traffic • Power management allows a node to doze off • Spread Spectrum Þ No licensing required.Three Phys: Direct Sequence, Frequency Hopping, 915-MHz, 2.4 GHz (Worldwide ISM), 5.2 GHz, and Diffused Infrared (850-900 nm) bands.

  13. 5.2 GHz Hiperlan 2.4 GHz (ISM) Why 2.4 GHz? IEEE 802.11 5.8 GHz (ISM) 5.2 GHz (Future?) 5.2 GHz (Future?) 2.4 GHz (ISM) 2.4 GHz (ISM) 1.9 GHz WinForum 915 MHz (ISM) U.S. Europe Japan

  14. Hidden Node Problem • C cannot hear A. It may start transmitting while A is also transmitting  A and C can't detect collision. • Only the receiver can help avoid collisions A B C

  15. MobileNode AccessPoint Ready to send Clear to send Data Ack 4-Way Handshake

  16. IEEE 802.11 MAC • Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) • Listen before you talk. If the medium is busy, the transmitter backs off for a random period. • Avoids collision by sending a short message: Ready to send (RTS)RTS contains dest. address and duration of message.Tells everyone to backoff for the duration. • Destination sends: Clear to send (CTS) • Can not detect collision  Each packet is acked. • MAC level retransmission if not acked.

  17. Peer-to-Peer or Base Stations? • Ad-hoc (Autonomous) Group: • Two stations can communicate • All stations have the same logic • No infrastructure, Suitable for small area • Infrastructure Based: Access points (base units) • Stations can be simpler than bases. • Base provide connection for off-network traffic • Base provides location tracking, directory, authentication Þ Scalable to large networks • IEEE 802.11 provides both.

  18. IEEE 802.11 Architecture Server Ad-hocStation AccessPoint AccessPoint Station Ad-hoc Station Station Station Station 2nd BSS Basic Service Set Ad-hocnetwork

  19. IEEE 802.11 Priorities DIFS Contention Window • Initial interframe space (IFS) • Highest priority frames, e.g., Acks, use short IFS (SIFS) • Medium priority time-critical frames use “Point Coordination Function IFS” (PIFS) • Asynchronous data frames use “Distributed coordination function IFS” (DIFS) PIFS Random Backoff Busy SIFS Frame Time Carrier Sensed

  20. Time Critical Services CFP Repetition Interval • Timer critical services use Point Coordination Function • The point coordinator allows only one station to access • Coordinator sends a beacon frame to all stations.Then uses a polling frame to allow a particular station to have contention-free access • Contention Free Period (CFP) varies with the load. Contention-Free Period Contention Period DCF Access PCF Access Time Beacon

  21. Power Management • A station can be in one of three states: • Transmitter on • Receiver only on • Dozing: Both transmitter and receivers off. • Access point (AP) buffers traffic for dozing stations. • AP announces which stations have frames buffered.Traffic indication map included in each beacon.All multicasts/broadcasts are buffered. • Dozing stations wake up to listen to the beacon.If there is data waiting for it, the station sends a poll frame to get the data.

  22. IEEE 802.11 Security • Authentication: • New nodes issue a "request for authentication" • Network sends a block of random text. • The node encrypts it with network password and returns. • Currently, one shared secret key (password) per net. • The same encryption algorithm is used for privacy.Wired Equivalency Privacy (WEP) Algorithm is based on RC4 PRNT algorithm developed by RSA Data Security, Inc.

  23. Status and Future • 802.11 including both MAC and PHY approved June 1997. • More bandwidth in future by: 1. Better encoding: Multilevel modulation  8 Mbps 2. Fewer channels with more bandwidth  4 MHz channels. Or Entire ISM band for one channel. 3. Find another band. May get 150 MHz band in 5-GHz band. Fifteen 10-MHz channels with 15-20 Mb/s.

  24. HIPERLAN • High Performance Radio LAN • European Telecom Standards Institute (ETSI)'s subtechnical committee RES10. • 5.12-5.30 GHz and 17.1-17.3 GHz bands • Phy: 23.5 Mbps on 23.5 MHz, non-spread spectrum (GMSK) • MAC: CSMA/CA but different from IEEE 802.11 • Peer-to-peer only. • Power management: Nodes announce their wakeup cycle. Other nodes send according to the cycle. A low-bit rate header allows nodes to keep most ckts off.

  25. Wireless ATM: Terminology • Wireless Terminal Adapter: Allows a terminal communicate via wireless • Wireless Access Point: Allows a switch to communicate via wireless • Mobility Support Adapter: Allows a switch to maintain VCCs with Mobile terminals and switches Switch AccessPoint WirelessTerminalAdapter Terminal MobilitySupport

  26. Reference Configurations 1. Fixed Wireless Access 2. Mobile End-Users, 3. Mobile Networks 4. Ad Hoc Networks 5. PCS Access 6. PCS Interworking Fixed WiredATMNetwork Mobile Fixed Mobile

  27. ATM Interfaces • UNI: User Network Interface • NNI: Network-node interface • B-ICI: Broadband Inter-carrier interface PrivateUNI PublicUNI PrivateSwitch Computer Carriers PrivateNNI PublicNNI PublicSwitch PublicSwitch PrivateUNI PrivateSwitch Computer B-ICI PublicSwitch Carrier

  28. PNNI + M, UNI + M, B-ICI + M PNNI’, UNI’ B-ICI’ AAL Signaling AAL Signaling AAL ATM ATM ATM WAL WAL WAL WATM Protocol Stacks • Wireless Access Layer (WAL) includesPHY, MAC, and LLC layers. • M = Mobility enhanced = Handoff, Location, QoS • PNNI’, UNI’, BICI’ support transport of mobility info User Plane Control Planes

  29. Summary • Spread spectrum: Frequency hopping or direct sequence • Proprietary LANs: Photonics, RangeLan, ALTAIR • LAN Standards: IEEE 802.11, Hiperlan • Wireless ATM work is just beginning

  30. Wireless: Key References • For a detailed list of references see: http://www.cis.ohio-state.edu/~jain/refs/wir_refs.htm • E. Prem, “Wireless Local Area Networks,” Aug 97, http://www.cis.ohio-state.edu/~jain/cis788-97/wireless_lans • X. Cong, “Wireless ATM - An Overview,” Aug 97, http://www.cis.ohio-state.edu/~jain/cis788-97/wireless_atm • Baseline Text for Wireless ATM specifications, ATM Forum/btd-watm-01.06.txt, February 1998.

  31. I. Brodsky, “Wireless Computing,” Van Nostrand Reinhold, 1997. • R. A. Dayem, “Mobile Data & Wireless LAN Technologies,” Prentice-Hall, 1997 • J. Ahmadi, et al, “Design Issues in Wireless LANs,” J. of High Speed Networks, 1996, pp 87-104 • R. LaMaire, et al, "Wireless LANs and Mobile Networking: Standards and Future Directions," IEEE Communications Magazine, August 1996, pp. 86-94, http://www.comsoc.org/pubs/ci/comsoc/

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