[OpenSER-Users] SIP Trunk doesn't response to 200OK with an ACK

[Iñaki Baz Castillo]

El Monday 18 February 2008 14:33:25 Eric Phetteplace escribió:
> Sorry about that: Network Topology.
>
> 8.21.8.24 is the PSTN gateway (WAN IP)
>
> 192.168.2.5 UAS (simple IP phone, "PC to PC" no registrar, etc)
> 192.168.2.1 NAT Router with 192.168.2.10 in DMZ  WAN Address is 2.6.7.9 in
> my previous message.
> 192.168.2.10 OpenSER and RTPProxy.

Do you have then port forwarding in the router? I think so but please confirm 
it.

In that case the problem is simple: your OpenSer set a "Record-Route: 
192.168.2.10" so in the next in-dialog message from the UAC or UAS it will be 
routed to that IP.

Note that:

- Your PSTN gateway calls to a PSTN number that is received in your OpenSer.
- The INVITE arrives to your OpenSer who adds  "Record-Route: 192.168.2.10".
- Then it sends the INVITE to the local phone (UAS).
- The UAS replies with 200 OK. This reply arrives to the OpenSer who 
adds "Record-Route: 192.168.2.10" and forwards it to the gateway.
- Now the gw has to send an ACK, but note that the ACK is an **in-dialog** 
request so it will go throught the IP set in "Record-Route" (192.168.2.10).
- Of course, your gw **cannot** route a request to a private IP so it's lost.

Solution: You must force OpenSer to set a custom IP (your router public IP) in 
the "Record-Route" header **just** when the request goes to the gateway. I'm 
not sure on how to do it but I think I've read sometime a about it in this 
maillist.

In conclusion: It's not a fault in your provider, but in your configuration.


-- 
Iñaki Baz Castillo
ibc at in.ilimit.es