sip helper

Hi All,

I just swapped our SG over for XG and things have gone smoothly except for a lingering issue with internal phone calls. I have two phones (i will call them A and B) that are unable to communicate with a third phone (C).

A->B and A->C calls get a recorded voice error from the PBX "incompatible ip media parameters" (and tcpdump shows a 488 message from SIP)

C->A and C->B calls go through but there is no audio in either direction

The phones and the PBX are on different subnets and are routed by the Sophos XG firewall.

If I do "set advanced-firewall bypass-stateful-firewall-config ..." to exclude A and B to PBX traffic, the internal calls work. If I exclude C to PBX traffic, calls break again.

These phones are 10+ years old. My currently theory is that one or all of A, B, and C are generating slightly buggy SIP packets and the Sophos is taking exception to them, although there are no logs anywhere.

Is it possible to apply any tweaks to the SIP helper module from Sophos to tell it to leave this internal traffic alone?

Thanks

James