Running notes from Wireless Routing and Multi-Hop Architectures, Christian Dubiel O'Reilly Emerging Technology Conference 2003 Cory Doctorow doctorow@craphound.com -- FWP Wireless: WiFi cellular systems to cover metro-scale areas What's a wireless routed network? Network where wireless nodes can route and switch traffic between themselves to interconnect out-of-range nodes Extends range and coverage of low-power radio, routes around obstructions to line-of-sight This is a wireless Internet, but subject to dynamic environment, interference, multipath fade, limited bandwidth Scaling challenges, throughput degredation across multiple hops (indroduced by interference and cumulative packet areas), and wireless links are not friendly to TCP/IP's coping strategies. In a wired network, slow connections are usually congestion, which leads to back-off. In a wireless net, slow connections are caused by interference. Backing off on an interfered link won't clear the congestion, 'cause there's nothing to clear. -- Mesh networking has its origin in military apps: self-organizing, self-healing, self-adapting mobile infrastructure. Not designed to scale, though: routing overhead scales at N^2. At a certain size, all traffic is control traffic. Multihop throughput -- with each hop, you suffer a throughput penalty at 1/N. 2 hops, 1/2 throughput, 3 hops, 1/3 throughput. This tails off over three+ nodes. Can be overcome with phased array and directional antennae. -- Multipoint to multipoint fixed wireless: last mile alternative to copper/co-ax. Can run point-to-point and overcome attenuation and line-of-sight limitations. Doesn't provide area coverage -- you can't just open your laptop and go. -- Routed radio access network Broad coverage, not just interconnection Independent of underlying wired infrastructure Scalability, speed, relaibiity, flexibility Not a device-to-device/P2P interconnection netowrk -- optimized for access, not interconnection 802.11 relies on wired infrastructure for backhaul, 802.11 is limited to the unlicensed band -- Big stick approach: find a mountain and put your antenna on top of it. But amplification won't let remote stations connect to you, only you connect with them. Better approach: cellular WiFI -- minimizes the effect of harmful interference. -- Q&A: Software Defined Radio is really cool. I hope it becomes legal soon. This decouples providing coverage from providing capactiy.