Re: [lwip-users] Retransmission timeout

[Kieran Mansley]

On Fri, 20 Jun 2003, Zschocke, Florian wrote:

> 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?  From taking a quick look at the code a
retransmission will occur when the number of coarse timer ticks since
the last segment was output (pcb->rtime) is greater than (the
round trip estimator) pcb->rto.

pcb->rto seems to be interpreted (when it is used) as being in units of
TCP_SLOW_INTERVAL, but I haven't checked to make sure that things that set
it also interpret it in this way.

The thing that makes me suspicious is I see retransmissions begin much
sooner than 25 min.  I am however using an older version of the source, so
maybe we've introduced a bug since then.  Are you seeing an actual problem
or just thought it was wrong when reading the source?

Thanks!

Kieran