David Schwab And Prof. Ralph Deters Wireless Networking David Schwab And Prof. Ralph Deters

What Is Wireless Networking? The use of infra-red or radio frequency signals to share information and resources between devices A hot computer industry buzzword: IBM Ad Series Wireless Broadband, 3G wireless, WAP, iMode, Bluetooth Mobile Internet Ubiquitous? Global? Revolutionary? “Think, Bill, Think”

Features of Wireless Networks: Hidden Node Problem Spread Spectrum: Frequency Hopping Spread Spectrum Hops distinct channels within a wide frequency band Hopping code determines channel sequence Different hopping patterns can co-locate Direct Sequence Spread Spectrum (DSSS) Modulates each bit with a chipping code Different chipping codes form separate channels Differences: FHSS has shorter range, lower max. speeds DSSS has Higher cost, power, and interference Hidden Node: Node A can see Node B, Node C can see node B, but node A cannot see node C. A may transmit while B is listening to C. 802.11 receivers uses RTS (Ready to send) and CTS (Clear to send) signals – Optional on transmitters. Spread Spectrum: Shrinks bandwidth, increases S-N ratio DHSS: Orthogonal hopping patterns never interfere FCC requires: 75+ channels, 400ms dwell time IEEE 802.11: 22 hop patterns over 79 1MHz channels Max. 2 Mbps DSSS: FCC requires: 10 – 20 bit chipping code IEEE 802.11: 11-bit chipping codes, 3 built-in codes = 3 channels More than three separate networks interfere Speeds of up to 11 Mbit/s Outdoor ranges of up to 10 km w/ line of sight.

Frequencies ISM – Industrial, Scientific, Medical Unlicensed Worldwide Power, time-sharing regulated (DSSS / FHSS) Short Range Devices (SRD) Includes: Microwaves, Cordless Phones Ranges: 902 – 928 MHz 2.4 – 2.4835 GHz 5.725 – 5.850 GHz Older cordless phones operated in 900 MHz. New are 2.4 GHz. Microwaves do not interfere with most 2.4 GHz devices. Uses short bursts. X10 Video senders are likely in violation of FCC specs. Three or more different 2.4 GHz devices in the same house will interfere.

Two 2.4GHz Standards: IEEE 802.11 Bluetooth Fast (11B) High Power Long range Single-purpose Ethernet replacement Easily Available Apple Airport, iBook, G4 Bluetooth Slow Low Power Short range Flexible Cable replacement “Vapourware” Anoto, Test cards, phone Take a closer look at 802.11, and the technology underlying it. 802.11 = 10baseT replacement Bluetooth = USB replacement Talk about Bluetooth later in lecture.

IEEE 802 Working Groups: LAN / MAN Standards Group (Ethernet) http://standards.ieee.org/wireless/ 802.15: Wireless Personal Area Networks (WPAN) 802.15.1 - 1Mbit/sec WPAN/Bluetooth 802.15.2 - Coexistence in Unlicensed Bands 802.15.3 - 20+ Mbit/sec High Rate WPAN for Multimedia 802.15.4 - 200kbit/sec max for interactive toys, sensor 802.16: Broadband Wireless Access Standards Fixed, Point-to-Point 802.11: Wireless Local Area Networks (WLAN)

IEEE 802.11 Organization Tree: OFDM = Orthogonal Frequency Division Multiplexing MAC = Medium Access Control

Disadvantages of 802.11: Older and newer cards are incompatible Reinforced concrete, tinted glass block signal No standard for hand-off between base station High power consumption in laptops Single hop routing Two separate modes: “Ad Hoc” LAN Client – Gateway Older devices DHSS, new devices DSSS. Old DSSS limited to 2 Mbit/s The high power consumption severely limits battery life. For this reason, few 802.11 cards are available for handheld devices. Different base stations incompatible. Peer-to-peer and Client-Gateway connections only – no Multi-Hop

Multi-Hop Ad Hoc Wireless Networking Routing protocols used to improve wireless connections Infrastructure-free, dynamic True Peer-to-Peer routing Fault tolerant Users allowed free movement Peers do not have a central database, gateways act as peers Transparently re-route packets if destination not found Easier installation of new computers More overhead – route discovery, updates Requires intelligent protocols Must accommodate lossy connections, handoffs, restricted bandwidth, interference, disconnections

DSDV Destination Sequenced Distance Vector Each node maintains lookup table Neighbours periodically exchange tables New node detection triggers table updates Lookup tables contain distance, next hop and sequence numbers, indexed by destination node Distance and sequence info determine when an entry is updated with new route The periodic exchange creates constant network overhead – level depends on what period specified Updates are propagated through the entire network Stale tables in the network cause packet loss with high node mobility Delivery ratio drops if triggered updates disabled, or if update period lengthened. No alternate delivery routes stored – Wait until update At speeds above 20 m/s in simulations, DSDV fails to converge

TORA Temporally Ordered Routing Alogrithm No periodic updates Multiple paths Node “height” used to find path Uses sup-optimal paths On-demand protocol Minimal correction propagation Like water flowing down a hill, TORA calculates a height (distance from destination) for each node between itself and the destination. The packet then travels to the next adjacent node with the lowest height. Sub-optimal paths used to avoid calculating another route. Detection of a disconnect raises neighbours to local peaks High storage cost – a value for each source-destination pair Routing loops can develop after a disconnect, if no synchronization occurs after height is raised.

DSR Dynamic Source Routing Path calculated at beginning of transfer Each packet carries the entire path Highest delivery ratio in high-speed simulations Developed by Carnegie Mellon University – NS2 wireless extensions, wireless test bed, Wireless Andrew Larger per-packet overhead than other routing protocols Nodes cache routing data Nodes can eaves-drop on packets passing near them – update cache Cache can store alternative routes Can query neighbours’ caches (limited distance route request) before flooding the network

Tools Free, Open-Source *NIX simulation tools: Ns2 Network Simulator, version 2 Emulation CMU Wireless Extensions Ad-Hockey Visualization tool for NS2 Ns is a discrete event simulator targeted at networking research. Ns provides substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless (local and satellite) networks. Originally developed by Berkeley, now maintained by The University of Southern California Information Systems Institute Only 2D simulations, Z axis ignored. Connections are on or off, no signal degradation. Two antenna models: free space and two-ray-grounded. NS2 features an emulation function which allows it to run a simulation trace in real-time over a network. Packets can be delayed or dropped by Ns, depending on the level of traffic and connectivity being simulated. CMU developed a set of extensions to NS2 to enable 802.11 simulations. These extensions are now part of the core NS2 program. CMU also developed Ad-Hockey. Ad-Hockey is a visualization tool which reads the trace files (output) of NS2 ad-hoc wireless scenarios. Also has some limited ad-hoc wireless scenario design capabilities.

Ad-Hockey Screenshot Three Nodes, two waypoints visible. Can add a pause time to each waypoint. Can control speed / arrival time for each waypoint. Ad-Hockey shows transmit / receive range + graph of connections.

Bluetooth Think USB, not Ethernet Created by Ericsson PAN - Personal Area Network 1-2 Mbps connections 1600 hops per second DHSS Includes synchronous, asynchronous, voice connections Piconet routing Small, low-power, short-range, cheap, versatile radios Usage Models: Three-in-one Phone Internet connection Ultimate headset Three-in-one-phone: When at home, use home gateway, when on road use cell tower, act as walkie-talkie when near enough. Internet connection: When at home, use home gateway. When on road use cell phone. When in office, use office gateway. Ultimate Headset: Computer, cell phone, telephone gateway, CD player, Discman, etc.

More Bluetooth SIG: Special Interest Group Trouble: http://www.bluetooth.com 2164 member companies Including 3Com, Ericsson, IBM, Intel, Lucent, Microsoft, Motorola, Nokia, Toshiba, etc. Bluetooth Specification (v1.1) Trouble: Not an Ethernet replacement Incomplete specification Incompatible implementations Delayed products Low demand Predictions still optimistic Problems: Bluetooth has been mis-labelled by many journalists and companies as being a wireless networking technology. The connection sequence described in the specs is very rough. No description of how a piconet organizes itself. Each company wants their products to work only with products from the same company Tests are being run on products to ensure compatibility. Bluetooth sales predictions are still very high (millions of phones by end of 2002).

Security Wireless sniffers IEEE 802.11: ESSID – Extended Services Set ID WEP – Wired Equivalent Privacy 40 bit RC4 (RSA) encryption “Resurrecting Duckling” paper – April 1999 Sleep-Deprivation Attack “Imprinting” wireless devices Bluetooth Security Rapid hop sequence Short range Encrypted transmissions The ESSID is needed to connect to a given 802.11 network. Connections can also be restricted by MAC address, although this is less reliable. Some vendors offer higher levels of encryption. Other vendors do not even implement WEP level security. Resurrecting Duckling – imprinting, resurrecting, sleep-deprivation attacks. Bluetooth devices switch frequencies 1600 times every second. They also limit their output power to a minimum, making eavesdropping very difficuly.

Guerrilla.net An underground alternative to the wired Internet A grassroots movement established in 1996 802.11 Wireless LAN cards Roof mounted antennae Free software (FreeBSD) Multi-hop routing, Internet connectivity About $800 per node Other networks popping up in SF, Seattle, London From Consume.net: “Fed up with being held to ransom in the local loop, phased by fees to ISP's, concious of community? OK so lets build a fresh network, one that is local, global, fast, expanding, public and user-constructed.” Co-operating ISP’s offer high speed internet. Legal issues covered by agreement. Lobbying the FCC for spectrum allocation for non-profit telcos. Dubbed “Free-network” movement – similar to free software, Napster, internet itself. Price is 1/3 what it would have been a couple years ago. Pulling antennae from Apple computers Catching on: SFLan, San Fransisco Consume.net, London Seattle Wireless, Seattle Problems: Scalability, abuse, tragedy-of-the-commons, no quality-of-service guarantee (same complaints made about TCP/IP)

Future of Wireless Better simulations + movement models Better security Wider selection Lower prices Less configuration More end-user focus Better software Less visible More popular Simulators with signal fade, movement models with groups. High levels of encryption, faster hopping / longer chipping keys More computer vendors will ship w/ 802.11 cards or Bluetooth (IBM, Compaq). Apple likely to lead the push for Bluetooth (after USB, Firewire, 802.11 success). Currently: buy network card, configure network, add clients Tomorrow: built-in card, plug and play configuration, clients perform resource discovery – Grandma-level wireless Software: Better drivers, better media streaming, better routing - Maxwell Dworkin building in Harvard.

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