[olsr-dev] Topology link quality

[Thomas Lopatic]

Hi Dries.

[code questions deleted, it should be possible to clarify this by means
of the debug output]

> node ip = 10.3.246.1
> 
>       *** olsr.org - 0.4.10 (Feb  2 2006) ***
> 
> --- 06:54:31.25 ---------------------------------------------------- LINKS
> 
> IP address       hyst      LQ     lost   total  NLQ    ETX
> 10.3.245.1       0.000  0.100  0      20     1.000  10.00
> --- 06:54:31.25 ------------------------------------------------ NEIGHBORS
> 
> IP address       LQ     NLQ    SYM   MPR   MPRS  will 10.3.245.1      
> 0.100  1.000  YES     NO    NO    3 
> --- 06:54:31.25 ------------------------------------------------- TOPOLOGY
> 
> Source IP addr   Dest IP addr     LQ     ILQ    ETX
> 10.3.245.1       10.3.246.1       0.098  1.000  10.20
> 
> 
> In the topology the link from 10.3.245.1 to 10.3.246.1 states LQ as
> 0.098, but IMHO it should be 1.000 and vice versa, not?

The LQ column in the "LINKS" section says how good the link from our
neighbour to us is. As there aren't any acknowledgements in OLSR, we can
only measure the packet loss among the packets that we receive. So, the
value 0.1 is for packets sent across the link 10.3.245.1 -> 10.3.246.1.

That's why 10.3.245.1 uses this value as LQ in its TC messages, that's
why we use a link's NLQ as link_quality and its LQ as
inverse_link_quality in our TC messages.

The link quality (LQ) measured by a node always covers the direction
from the node's neighbours to the node. For the other direction, the
node's neighbours have to tell the nodes their values (NLQ).

-Thomas