Hi,

I have an SL2100 with 6 remote IP phones connected via a VPN. Calls into extensions at the site with the pbx work fine, as do external calls inbound and outbound

What we cannot do is make calls between extensions at the remote site, if we dial the extension we here the ringing dialtone but then when the extension picks up there is no audio and after 10 seconds the call is ended and the IP phone displays hang up

This is only happening on the internal calls between the extensions at the remote site,

In terms of the config for the phones they have

SIP 1st Server Address: internal IP of pbx
Access mode: Normal
SIP 1st Server Port 5080
NAT traverse Mode: Dynamic
WAN Mate IP: Internal IP of the PBX
WAN Mate Port: 5080

Could anybody let me know what may be going wrong?

Check your router settings at each location.


If you have an VPN there is not need to configure NAT, WAN settings.

Try turning off Peer to Peer for the IP phones in 15-05-50

Do the phones have a CAP key on them?

Ok first you are on a VPN you don't use NAT tranverse at all for those. Turn that off.

In 10-58 DEFINE your internal VPN network so everything is routed correctly and make sure everything is on the same subnet.

This is the answer, I've run into this problem before and disabling peer to peer solved it.

But as CoralTech said you don't need NAT at all if he/she is using a VPN.

Peer to peer has nothing to do with nat afaik, It forces the calls to go through the pbx if it's off.
when it's on the remote phones try to establish a call session between them to save channel resources from the system but in my experience this always caused me audio problems.

would PEER to PEER also explain why I have an audio talk path on an MLC Phone using NAT, but when on the local Wifi have no talk path at all?