Wireless Local Area Networks: Recent Developments

Wireless Local Area Networks: Recent Developments Ohio Highway Patrol

Raj Jain The Ohio State University Columbus, OH 43210 http://www.cis.ohio-state.edu/~jain/ Raj Jain

The Ohio State University

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Overview q

Spread Spectrum

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Wireless local area networks

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Wireless LAN standard: IEEE 802.11

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Hiperlan

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Wireless ATM Raj Jain


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Mobile vs Wireless Mobile

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Wireless

Mobile vs Stationary Wireless vs Wired Wireless ⇒ media sharing issues Mobile ⇒ routing, addressing issues Raj Jain


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Frequency Hopping Spread Spectrum Frequency

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50 ms Time 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 Raj Jain


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Spectrum Signal

Noise

(a) Normal

Noise

Signal

(b) Frequency Hopping

Raj Jain


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Direct-Sequence Spread Spectrum 0

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Data 01001011011011010010 Frequency

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Time 5µs 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 Raj Jain


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DS Spectrum Time Domain

Time

Frequency Domain

(a) Data

(b) Code

Frequency

Frequency Raj Jain


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Wireless LANs

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IR ⇒ Line of sight, short range, indoors RF ⇒ Need license Spread-Spectrum: Resistance to interference µwave

Infrared

Visible

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Ultraviolet x-rays

109 1010 1011 1012 1013 1014 1015 1016 1017 1018 Raj Jain


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Wireless LANs Line of Sight

Infrared

Radio

Diffuse Spread Spectrum

Narrowband Motorola 2.4 GHz 5.7GHz ALTAIR

InfraLAN Photonics Collaborative 902 GHz Proxim DS FH DS FH Windata RangeLAN Freeport NCR WaveLAN Proxim Telesystems RangeLAN2 ArLAN The Ohio State University

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Raj Jain

Wireless LAN Products q q q q q q q q q q q

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 Raj Jain


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WLAN Products (Cont.) q q q q q q q q q q

Photonics - Collaborate Series Proxim- RangeLAN2 Solectek - AirLAN Spectrix - SpectrixLite TELXON - ARLAN 600 Travelling Software - Airshare WiLAN - 902-20 Windata - FreePort Xerox - PARCTAB Xircom - NetWave


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Raj Jain

IEEE 802.11 Features q q q q q q

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 ⇒ 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. Raj Jain


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Why 2.4 GHz? IEEE 802.11 5.8 GHz (ISM) 5.2 GHz (Future?)

5.2 GHz Hiperlan

5.2 GHz (Future?)

2.4 GHz (ISM)

2.4 GHz (ISM)

2.4 GHz (ISM)

1.9 GHz WinForum 915 MHz (ISM) U.S.


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JapanRaj Jain

Hidden Node Problem

A

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C

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 Raj Jain


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4-Way Handshake Access Access Point Point

Ready to send

Mobile Mobile Node Node

Clear to send Data Ack

Raj Jain


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IEEE 802.11 MAC q

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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.

Raj Jain


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q

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Peer-to-Peer or Base Stations?

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


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IEEE 802.11 Architecture Server Server

Access Access Point Point Station Station Station Station Basic Service Set

Access Access Point Point Station Station 2nd BSS

Ad-hoc Ad-hoc Station Station Station Station Ad-hoc Ad-hoc Station Station Ad-hoc network Raj Jain


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IEEE 802.11 Priorities DIFS PIFS Busy SIFS

Contention Window Random Backoff Frame

Time Carrier Sensed q Initial interframe space (IFS) q Highest priority frames, e.g., Acks, use short IFS (SIFS) q Medium priority time-critical frames use “Point Coordination Function IFS” (PIFS) q Asynchronous data frames use “Distributed coordination function IFS” (DIFS) Raj Jain


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Time Critical Services CFP Repetition Interval

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Contention-Free Contention Period Period PCF Access DCF Access Time Beacon 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. Raj Jain


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Power Management A station can be in one of three states: m Transmitter on m Receiver only on m Dozing: Both transmitter and receivers off. q Access point (AP) buffers traffic for dozing stations. q AP announces which stations have frames buffered. Traffic indication map included in each beacon. All multicasts/broadcasts are buffered. q 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. The Ohio State University Raj Jain q

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IEEE 802.11 Security q

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Authentication: m New nodes issue a "request for authentication" m Network sends a block of random text. m 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. Raj Jain


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Status and Future q

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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.

Raj Jain


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

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Wireless ATM: Terminology Terminal q

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Switch Wireless Terminal Adapter

Access Point

Mobility Support

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 Raj Jain


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Reference Configurations 1. Fixed Wireless Access 3. Mobile Networks 5. PCS Access

Fixed Fixed

2. Mobile End-Users, 4. Ad Hoc Networks 6. PCS Interworking

Wired ATM Network

Mobile

Mobile Raj Jain


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ATM Interfaces Private Private Public Computer UNI Switch UNI Carriers Private Public Public Public NNI Private Switch Switch Private NNI Computer Switch UNI B-ICI q UNI: User Network Interface Public q NNI: Network-node interface Switch q B-ICI: Broadband Inter-carrier interface Carrier Raj Jain


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WATM Protocol Stacks q

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Wireless Access Layer (WAL) includes PHY, MAC, and LLC layers. M = Mobility enhanced = Handoff, Location, QoS PNNI’, UNI’, BICI’ support transport of mobility info

AAL ATM WAL User Plane

PNNI + M, UNI + M, PNNI’, UNI’ B-ICI + M B-ICI’ Signaling AAL Signaling AAL ATM ATM WAL WAL Control Planes

Raj Jain


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Summary

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

Raj Jain


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Wireless: Key References q

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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/cis78897/wireless_lans X. Cong, “Wireless ATM - An Overview,” Aug 97, http://www.cis.ohio-state.edu/~jain/cis78897/wireless_atm Baseline Text for Wireless ATM specifications, ATM Forum/btd-watm-01.06.txt, February 1998. Raj Jain


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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/ Raj Jain


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