Thursday, October 2, 2008


Roofnet is an unplanned 802.11b mesh network that aims to provide high performance Internet access. Roofnet has the following design advantages: Unconstrained node placement, omni-directional antennas, multi-hop routing and throughput-optimized routing. While these advantages ease deployment, the question is how it affects the performance of the network.

I like the deployment scenario of Roofnet – volunteers who just signed up and installed the node on their roof tops. Routing happens over a combination of link-state and DSR-style querying. The installation is fairly straightforward, and nodes form a wireless ad-hoc network among them. I would have liked to see a photo of the antenna installed on the rooftop along with node. Are the nodes to which the antennas are connected, placed on the roof top too? What are the effects of wear and tear, pollution etc.? In any case, a nice follow-up work to this could be something like “The Operational Difficulties of maintaining a wide-spread mesh network” (like the TIER paper in NSDI 2008 – I loved it!).

The evaluation determines performance of Roofnet based on the following measurements:

  1. Multi-hop TCP data obtained using a one-way bulk TCP transfer between each pair of Roofnet nodes (15 seconds)
  2. Single-hop TCP data measured using direct links between nodes
  3. Loss matrix that quantifies the loss rate between each pair of nodes using 1500-byte broadcasts
  4. Multi-hop density: TCP throughput between a fixed set of four nodes for different Roofnet nodes

Another aspect of their evaluation could be to see at what density does it become too chaotic that there is just way too much interference. But “living with the interference” is a theme in MIT’s current research…so it seems to be consistent.

I am personally not a fan of multi-hop networks in real life. I have never been able to get its utility in a generic sense (I understand it is clearly useful for special cases like sensor nets). And in any case, Roofnet isn’t too relevant for an urban setting where each user is likely to have a gateway anyway. But it would be interesting to see how Meraki does (or has done).

But overall, I found this paper to be quite interesting and smart but I wouldn’t vote for keeping it on the list.

1 comment:

Akhil Dhar said...

That would be an interesting follow-up study indeed. Do any of these external physical factors affect the performance of outdoor satellite networks? I'd imagine that similar effects would be seen for this architecture.