On Thursday 30 July 2009 22:32:04 Yang Su wrote:
- Similar to what Marek proposed. But push it to the extreme: switch to a
neighbor only when it has the best tq AND it has the newest seqno. This fix along seems to already solve the looping problem in the test cases. It reduces the rerouting time from more than 1 minutes to less than 15 seconds. Marek: I also tried the patch you sent. It didn't help in this setup.
Changing the route based on the (fastest) sequence number has some drawbacks which we experienced before (BATMAN III). It tends to discriminate longer but better routes and favors short paths. In some asymetric link (worst case) scenarios it would route against all odds, simply because receiving a fast packet (newest seqno) does not mean we can send the same way back. If possible I'd like to avoid this strict seqno check.
I attached another patch which will conduct a route switch only if the TQ of the sending neighbor is better than our current best route (no negative switching anymore). I tested the patch here and it works so far but my environment is less controlled than yours. Could you perform the same test on your setup ?
If you intend to experiment with other ideas watch out for the sequence number as it will overflow. A simple "greater than" check might lead to strange results. Also, updates_routes() checks for changed HNA messages even if the next hop does not change.
- Relaxed echo cancellation. This is based on the following observation:
the TQ value that a node puts into OGM is completely decoupled with "from which neighbor this OGM is received". As a result, the TQ value contained in the echoed OGM represent the real TQ value at the neighbor which echoed this OGM. The current echo cancellation implementation just drops all the echoed OGM. This may prevent the node from updating the information towards the neighbor that echos the OGM. In the extreme case, the information towards that neighbor may becomes completely stale (similar to what happens in case 2). The change I made: Always check the TQ contained in the echoed OGMs. When it is worse than the avg TQ towards that neighbor, we use this TQ reading to update the avg TQ towards that neighbor. This change didn't show any effect during the chain tests. However, I still include this change in the patch to bring up the discussion.
Right, every node will emit his currently best TQ value but I did not understand how we can use that. If we send him a better TQ he will send back that number. If we send a bad TQ he will send his good number. Furthermore, each hop will apply some asymetric / hop / wifi penalty that we pull into our routing database ?
Regards, Marek