SDP contact IP not honored

[loowens]

All, I am testing 3CX currently as a possible alternative to Trixbox. I have been using Trixbox for 2 years now without a lot of trouble, but it seems to have little problem that require re-tweaking after almost every upgrade. After a few hours of working with 3CX and connecting it to a Metaswitch via a SIP binding (trunk) I have found that the connection IP in the SDP message is not the one I have configured in Settings or under the VOIP provider section of 3CX. It is sending it with the external IP of my firewall (NAT). This is the same setup on the firewall I use with Trixbox without any issues and I am wondering if there is any way to get 3CX to let me define that address in the message.

I have the STUN server off and the IP defined there, I also have the same IP defined under the VOIP provider section "Which IP to use in Contact Field". The call Invites setup fine, but RTP streams to the wrong inbound address and is dumped. I know I could make a change to the firewall and map some ports, but I want to understand why the settings aren't working as I'd expect them to.

Thanks

 

[loowens]

Alright I figured out the SDP part. Seems that you have to leave the VOIP Provider settings as "externally resolve Use Stun server", Then it uses the defined IP you have setup under the network settings for the STUN server. Now that I have audio another problem arose. Even though I have G.729 selected as the only supported codec the packet trace shows g.711 being used. Any ideas what to look at here?

 

[loowens]

Well, I thought it was figured out. This morning I came back in to the office and now it's returned to the behavior of not inserting the specified IP in the SDP section of the INVITE.

I must say the software seems very twitchy and unreliable in the sense that it seems to behave differently on different attempts of the same call.

 

[N_G]

I suggest you review the settings require for 3CX on the firewall. Its probably not setup to the requirements.

Note also that in the Free edition, you do not have any G729 licenses so it would be forced to use G711.