[Serusers] t_on_retransmission route

[Hendrik Scholz]

Hi!

We were poking the idea around of having an optional route
that would be invoked upon a retransmission.
The fr timers all fire way too late if you'd have to implement
some sort of fallback if your peering partner or PSTN gateway died.

I magine a routing mechanism much like t_on_failure() / failure_route()
to allow something like this:

- set transmission timer via AVP / t_set_fr() like
- t_on_retransmission(1);
- t_relay_to_udp()

and then you'd have something like

retransmission_route[1] {
   # select new gateway
   t_relay_to_udp()
}

The retransmission route should be invoked if no provisional (i.e.
100 Trying) nor final response was received within the given interval.
I'm not sure about how to handle TCP connections, though. A simple
TCP ACK might be enough to assume the other side is up and happy
to answer our request.

This would allow for redirecting traffic without having to wait for
a final response (408 timeout).
The timer value would be fr_timer - fr_inv_timer starting at the same
time as fr_timer itself.

Last but not least I'm not sure about the impact of having quite
a lot of timers firing after a couple of msecs.

If anybody thinks this would make sense I'd give it a try ;)

Cheers,
  Hendrik

-- 
Hendrik Scholz - <hscholz at raisdorf.net> - http://www.wormulon.net/
drag me, drop me - treat me like an object