Wireless Data Networking

Wireless Data Networking Ohio Highway Patrol

Raj Jain The Ohio State University Columbus, OH 43210 Handouts: http://www.cis.ohio-state.edu/~jain/cis788-97/ Email questions to [email protected] Raj Jain

The Ohio State University

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Overview

Spread Spectrum q Wireless wide area networks: CDPD and Metricom q Wireless local area networks q Wireless LAN standard: IEEE 802.11, Hiperlan q Wireless ATM q Mobile IP Note: wireless phone services and standards not covered. q

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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 Narrowband interference can't jam Raj Jain


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Spectrum Signal

Noise

(a) Normal

Noise

Signal

(b) Frequency Hopping

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Direct-Sequence Spread Spectrum 0

1

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 WAN Services

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4.8 kbps to 19.2 kbps nominal Throughput 2 to 8 kbps Wired backbone using leased lines Packetized short transmission Email, stock quotes, weather Options: ARDIS, RAM Mobile Data, Cellular, Cellular Digital Packet Data (CDPD), and Metricom Raj Jain


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Cellular Digital Packet Data (CDPD) q q q

Originally named “Celluplan” by IBM Allows data to use idle cellular channels Data hops from one channel to next as the channels become busy or idle

Voice Call Idle Channel The Ohio State University

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Data packets Raj Jain

CDPD q q q

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Backed by 9 major service providers Nationwide cellular packet data service Connectionless and connection-oriented service Connectionless ⇒ No ack, no guarantees Connection-oriented ⇒ reliable delivery, sequencing, flow control Point-to-point and multipoint connections Quickly hops-off a channel grabbed by cellular system. Currently, dedicated channels. Raj Jain


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Metricom Spread-Spectrum in 902-928 MHz band q In-building, campus, and metropolitan area networking q Nearby units can communicate directly. q If the intended destination is not directly reachable, go via a “node” through the network. Up to 56 kbps. q Nodes are cheap (less than $1,000) q Flat monthly rate based on speed only Ref: http://www.metricom.com/ricohom.html q

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 Visible

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µwave

Ultraviolet x-rays Infrared 109 1010 1011 1012 1013 1014 1015 1016 1017 1018 Raj Jain


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Wireless LANs Infrared Line of Diffuse Sight

Radio 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

IEEE 802.11 Features q q q

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1 and 2 Mbps Supports both Ad-hoc and base-stations 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. Supports multiple priorities Supports time-critical and data traffic Power management allows a node to doze off Raj Jain


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Hidden Node Problem

A

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B

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

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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.

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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

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CFP Repetition Interval 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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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 Group officially began August 96 q Wireless Access Layer (WAL) includes PHY, MAC, and LLC layers. q M = Mobility enhanced = Handoff, Location, QoS q PNNI’, UNI’, BICI’ support transport of mobility info PNNI + M, UNI + M, PNNI’, UNI’ B-ICI + M B-ICI’ AAL Signaling AAL Signaling AAL ATM ATM ATM WAL WAL WAL User Plane Control Planes q

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Reference Configurations q q q q

Fixed Wireless End user mobility Network mobility Ad-hoc

Fixed Fixed

Wired ATM Network

Mobile

Mobile Raj Jain


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Mobile IP: Features q q

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You can take you notebook to any location Finds nearby IP routers and connects automatically. You don't even have to find a phone jack. Only "Mobility Aware" routers and mobile units need new s/w. Other routers and hosts can use current IP No new IP addresses or address formats Secure: Allows authentication Also supports mobile networks (whole airplane/car load of mobile units) Raj Jain


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Mobile IP: Mechanisms Home net Mobile Home Node Agent

Correspondent

New Mobile net Foreign Node Agent Correspondent

Home Intermediate Foreign Routers Agent Agent

IP Header IP Header To: COA, ip-ip To: Mobile, tcp

Mobile Node

Info Raj Jain


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Mechanism (Cont) q

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q

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Mobile node finds foreign agents via solicitation or advertising Mobile registers with the foreign agents and informs the home agent Home agent intercepts mobile node's datagrams and forwards them to the care-of-address Care-of-address (COA): Address of the end-of-tunnel towards the mobile node. May or may not be foreign agent At COA, datagram is extracted and sent to mobile Raj Jain


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Summary

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Spread spectrum: Frequency hopping or direct sequence WANs: ARDIS, RAM, Cellular, CDPD, Metricom Proprietary LANs: Photonics, RangeLan, ALTAIR LAN Standards: IEEE 802.11, Hiperlan Wireless ATM work is just beginning Mobile IP allows a node to move with same address 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 R. A. Dayem, “Mobile Data & Wireless LAN Technologies,” Prentice-Hall, 1997 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/ Baseline Text for Wireless ATM specifications, ATM Forum/btd-watm-01.04.txt, September 1997. Raj Jain


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References (Cont) q

RFC 2002, "IP Mobility Support", 10/22/1996, 79 pp., http://ds.internic.net/rfc/rfc2002.txt

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Credits This MBone transmission was made possible by: q Mark Fullmer, OSU/UTS q Mike Iverson, OSU/UTS q Mike Douglas, OSU/UTS q Jayaraman Iyer, OSU/CIS q Sohail Munir, OSU/CIS

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Thank You!

Raj Jain


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