[lwip-users] Retransmission timeout

[Zschocke, Florian]

This maybe a stupid question, but I fail to answer it myself.

I understand that lwIP is using van Jacobson's algorithm for RTO
determination. But what is the minimum timeout value? The minimum timeout
before a retransmission is started? What I was able to deduce from the code
reads as if it would be 3000*TCP_SLOW_INTERVAL, i.e. 3000*500ms, i.e. 25min.
That seems a bit long thus I assume I'm missing something important here.

Thanks,
Florian.

[Kieran Mansley]

Post by Zschocke, Florian
This maybe a stupid question, but I fail to answer it myself.
I understand that lwIP is using van Jacobson's algorithm for RTO
determination. But what is the minimum timeout value? The minimum timeout
before a retransmission is started? What I was able to deduce from the code
reads as if it would be 3000*TCP_SLOW_INTERVAL, i.e. 3000*500ms, i.e. 25min.
That seems a bit long thus I assume I'm missing something important here.

Where do you get the 3000 from?

[Zschocke, Florian]

Post by Kieran Mansley
Where do you get the 3000 from?

Forget it, I got lost somewhere in the code and didn't follow VJ's algorithm
enough to understand how it can be decreased from the default. The 3000 came
from the initialization.

Post by Kieran Mansley
Are you seeing an actual problem or just thought it was
wrong when reading the source?

It was both. I was pondering over tcprtoMin and tcpRtoMax values and I also
didn't see retransmits. But it turns out that was for a completely unrelated
problem: the TCP timer never fired. :)

Florian.