Wireless Community Networks: Evolution and Technical Challenges Luiz A. DaSilva Bradley Department of Electrical and Computer Engineering Workshop on Nationwide Internet Access and Online Applications Dhaka, Bangladesh May 22-24, 2004
Agenda Wireless community networks: a definition Examples Applications: beyond WISPs Supporting technologies Open technical issues Concluding remarks
We offer a definition Community network (k&-'myü-n&-te 'net-"w&rk) A network providing wireless access to a community with minimal infrastructure planning or corporate participation, at low or no cost to end users
A very short history The idea started getting hold around 2000, with availability of inexpensive wireless technology (IEEE 802.11) Often started by hobbyists, with gradual interconnection of small networks Similarities to the evolution of amateur radio and the free software community Gradually becoming more organized, with organizations providing A means to register new nodes Technical support for novices A forum for discussion of issues Increased visibility
Common characteristics Grassroots effort, spontaneous deployment Driven by individuals or local governments Low cost, off-the-shelf (or home-made) technology Not for profit (or very minimal business models) Informal coordination FreeNetworks.org is a voluntary cooperative association dedicated to education, collaboration, and advocacy of the creation of free digital network infrastructures.
What it is not Cellular networks (2G/2.5G/3G/4G) Commercial hot spot service
Examples
Atlanta FreeNet A ( ) grassroots movement of community minded individuals that is dedicated to the improvement of life in Atlanta through the roll-out of free Wireless-Fidelity (Wi-Fi) hotspots. Coverage: Atlanta, GA, U.S. Started: 2001 Currently: 128 nodes Node map, Atlanta FreeNet Source: http://www.atlantafreenet.org
Air-Stream Aims to build a metropolitan wide area wireless network using off-the-shelf wireless hardware, by helping to interconnect smaller local wireless networks and encouraging participation Coverage: Adelaide, South Australia Adelaide node database, Air-Stream Source: http://www.air-stream.org
NYC Wireless Promotes deployment of open hot spots in public spaces Works with public and not-forprofit organizations Serves as an advocate for wireless community networks Coverage: New York city Currently: 187 nodes NYCWireless.net node database Source: http://www.nycwireless.net
Applications Wireless Internet Service Providers (WISPs) E-governance Support network for NGOs Multimedia communications Telemedicine Community webs and radio broadcasting E-mail, web browsing Collect and disseminate information Rural credit, agricultural databases Voice over IP, videoconferencing Augment public health services in rural areas Community newspapers, dissemination of radio content
Supporting technologies Wireless access: 802.11 802.11b (WiFi) and, increasingly, 802.11g Due to low cost of deployment, ubiquity of NICs Antennas Omni and directional antennas External antennas Broadband access to Internet Cable modems Digital Subscriber Line (DSL) Leased lines (T1) Server (e.g., a Linux box) Internet Broadband access AP w/ external antenna
IEEE 802.11b Specification released in 1999 2.4 2.483 GHz band Direct Sequence Spread Spectrum (DSSS) Data rates of up to 11 Mbps Data rates are automatically adjusted for noisy conditions, so can operate at 1, 2, 5.5 or 11 Mbps Infrastructure-based and ad-hoc modes of operation) Most widely implemented to date IEEE 802.11g specification is more recent Backwards compatible with 802.11b (same frequency band) Data rates of up to 54 Mbps
IEEE 802.11b Center frequencies 2442 7 2437 6 2432 5 2427 4 2422 3 2417 2 2412 1 Japan Eur. US / Can Freq. (MHz ) Channel 2484 14 2472 13 2467 12 2462 11 2457 10 2452 9 2447 8 Japan Eur. US / Can Freq. Channel
Wi-Fi Wireless fidelity The Wi-Fi Alliance certifies interoperability of 802.11- based products Non-profit organization founded in 1999 Over 200 members
A typical wireless community net node (1) Access Point Pigtail Low-loss cable External antenna May vary significantly in sophistication and capabilities May support firewall capabilities, dynamic addressing, expanded security features Connects to a server or wired LAN Cisco Aironet 350 Series Linksys WAP11
A typical wireless community net node (2) Access Point Pigtail Low-loss cable External antenna Needed to connect a wireless card to an antenna cable
A typical wireless community net node (3) Access Point Pigtail Low-loss cable External antenna Pigtail only extends 3 ft. or so Use low-loss cable to place external antenna at greater distances
A typical wireless community net node (4) Access Point Pigtail Low-loss cable External antenna Omni or directional Home-made or professional Antenna placement, height and directionality are crucial factors in determining range The famous Pringle s antenna
Prices (a rough idea ) Wireless Card and Coax: US$120-780 $50-150 card $30-80 pigtail $30-150 coax run $10-250 antenna $0-150 mounting hardware and mast Ethernet bridge: US$215-1050 $200-500 bridge $5-50 CAT5e cable $0-20 power supply to bridge $0-50 waterproofing $10-250 antenna $0-150 mounting equipment and mast
Open issues: mobility support (1) IEEE 802.11 originally meant to support nomadic computing, but not seamless mobility
Open issues: mobility support (2)
Open issues: mobility support (3) Some vendors have implemented proprietary protocols for communication among APs regarding currently associated stations, in support for handoff Not interoperable across APs from multiple vendors IEEE 802.11f working group is defining standard protocols for inter-ap communication Inter Access Point Protocol (IAPP) Re-association, authentication, exchange of buffered data between APs Mobile IP Home and foreign agents participate in tunneling data for the mobile node when away from its home network
Open issues: topology planning In many cases, no formal planning is done If a local government wants to establish a new community network, some coverage planning is advisable May borrow techniques for cell planning in 2G/3G networks
Open issues: security Clear need to preserve integrity and privacy of information over wireless networks IEEE 802.11 supports Wired Equivalent Privacy Known to have vulnerabilities to breaking encryption, presence of rogue access points, etc. IEEE 802.1x uses the Extensible Authentication Protocol (EAP) to authenticate each station through a central authentication server IEEE 802.11i developing a specification with tighter encryption, mutual authentication of stations and APs WiFi Protected Access (WPA) defines a subset of 802.11i, to address some limitations of WEP
Open issues: quality of service Especially important if WCN is to support a variety of services, beyond email and web browsing Must protect real-time and deadline-sensitive traffic from more elastic traffic IEEE 802.11e defines MAC-layer mechanisms for prioritized access to the medium Wireless Multimedia Enhancements (WME) is a vendor-driven initiative to provide some QoS while 802.11e does not take hold
Concluding remarks NGOs and local governments may have an important role to play in the deployment of community networks in developing countries Is 802.11 the right technology for these types of networks? Limitations in security, not meant to support seamless mobility But inexpensive and widely deployed The development of new technologies (e.g., 802.16/WiMax) and the deployment of mesh/ad hoc networks may change this landscape Complement and, in some cases, substitute current wireless community networks
Resources Wireless Community Network List: http://www.toaster.net/wireless/community.html Links to major wireless community network initiatives These, in turn, link to resources for setting up WCNs Book Rob Flickenger, Building Wireless Community Networks: Implementing the Wireless Web (ISBN 0-596-00204-1) Articles S. Jain and D. Agrawal, Wireless Community Networks, IEEE Computer, August 2003 D. Aguayo et al., MIT Roofnet: Construction of a Community Wireless Network, Proc. of MIT Student Oxygen Workshop 2003
Questions/Comments Luiz A. DaSilva Bradley Department of Electrical and Computer Engineering ldasilva@vt.edu (703) 535-3466 (703) 518-8085