[Olsr-dev] ETX Calculation

[Vincent, Michael - 0665 - MITLL]

We're using OLSR (0.5.6-r7) in a testbed where a vehicle moves away from a fixed point in a straight line.  As the signal weakens (LQ increases) we add a relay node directly between the fixed point and moving vehicle (on the straight line path).  The issue is that the ETX for the 2-hop path (via the relay) doesn't register better than the direct path until the packet loss on the direct path is way up.


I've read the Link Quality README (http://www.olsr.org/docs/README-Link-Quality.html) and it seems to indicate that the ETX for a multi-hop path is the sum of the individual paths (ETX1 + ETX2 ...).  Looking at the source code - this seems to be the case also.


We'd like to use the relay node quicker - that is, before the direct path suffers from horrible packet loss and the ETX for the multi-hop path takes over.  I think the summing of ETX without some 'scaling factor' is the issue.


I'm not a very skilled C programmer so my poking and tweaking the source code hasn't yielded much I the way of a solution.  Any recommendations on how to go about fixing this?


    Cheers.

-- 
Michael J. Vincent
MIT Lincoln Laboratory
Lexington, MA 02420