[OLSR-users] Link quality update

[Thomas Lopatic]

Hi there,

I've updated the link quality code a bit:

* It now uses ETX as a metric. Thanks to Andrew Nott for pointing out 
the differences on this mailing list. We now do not maximize

LQ1 * LQ2 * ... * LQn

any longer (LQ1 to LQn being the link qualities of the hops between us 
and the destination node), but minimize

1/LQ1 + 1/LQ2 + ... + 1/LQn

instead, which is what ETX suggests.

* If you set the debug level to 2 (either by giving "-d 2" on the 
command line or by saying "DebugLevel 2" in the configuration file) then 
a section with the heading "DIJKSTRA" will be printed, whenever the 
Dijkstra algorithm is run. Output looks, for example, as follows:

192.168.0.2:1 (one-hop)
192.168.0.72:2 <- 192.168.0.2:1 (one-hop)

Each line contains a path from the destination to us. Each IP address is 
followed by a colon and the cumulative cost of the path up to this IP 
address. In the above example, we have a (one-hop) neighbour 
192.168.0.2. As the link quality LQ of the link with this neighbour is 
1.0, the ETX value 1/LQ is 1. So, the total cost of the path is 1. 
192.168.0.2 is directly reachable and thus it is the only hop in this line.

192.168.0.72 is reachable via 192.168.0.2. That's what the second line 
says. So, each line starts with the destination and works its way to one 
of our one-hop neighbours. We already know that the ETX value for 
192.168.0.2 is 1. As the link quality between 192.168.0.72 and 
192.168.0.2 is also 1.0, the ETX value for this link is 1. So, the 
cumulative cost of the path is the cost between us and 192.168.0.2 plus 
the cost between 192.168.0.2 and 192.168.0.72, which is 2.

If the Dijkstra algorithm discovers nodes that we cannot reach, the last 
entry on the line will not be a one-hop neighbour, but the word "FAILED".

* With a debug level of 2 we now also print out the links reported by 
all other nodes in the network via TC messages. Each column contains the 
source address of the link (i.e. the node that reports the link), the 
destination address (i.e. the node that the reporting node can reach), 
the link quality for this link (for packets sent by the reporting node 
to the destination node) in the "LQ" column and the link quality in the 
inverse direction (for packets sent by the destination node to the 
reporting node) in the "ILQ" column.

* There has also been an update to the neighbour table debug output. It 
now contains an additional column "MPRS", which contains "MPRS" in case 
the neighbour has selected us as MPR, and which is blank otherwise.

-Thomas