This paper describes the design of a wireless mesh network. The key goal of the design is ease of deployment. So nodes are in unplanned locations and they use omni-directional antennas to avoid having to configure antenna placement. This necessitates a multi-hop routing and path optimization to provide adequate throughput.
The network is auto-configuring and has only some nodes that act as external gateways to the Internet. It uses an internal addressing system based on the MAC address of the Ethernet cards to route within the mesh. At the gateways, NAT is used to translate internal addresses to external ones. This means that connections are tied to a specific external gateway and cannot shift if network conditions change. However, new connections always use the "optimal" gateway.
To route within the wireless mesh each node uses Dijkstra's algorithm to choose the best path. The cost of each link is estimated using an "estimated transmission time" metric. This takes into consideration the throughput bit-rate of the link and the probability of delivery at that bit-rate. For example, "a single-hop route with 40% loss can deliver more data than a two-hop route with perfect links." By considering these trade-offs the node is able to maximize its throughput.
The authors deploy a system of 33 nodes and 4 gateways on rooftops in Cambridge Massachusetts by asking volunteers to install the nodes. They obtain an average throughput of 627 kbits/s with links having a median loss rate of 20%. The throughput is mostly dependent on the number of hops with just 89 kbit/s at 5 hops.
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