IVM Attendant not honouring codec priority

[synologic]

Hi,

 

we recently encountered a problem with IVM Answering Attendant after our upstream sip provider disabled audio transcoding on the calls (probably due to performance problems).

 

The setup we are running is as follows:

 

SIP Provider -> Draytek 2810 IP PBX -> IVM Attendant

 

A normal call from a terminal connected to either the IPPBX or directly to the sip provider, and uses g711U works fine, however, an external call (eg mobile, land line) is initiated like this:

PBX -> IVM:

 

v=0

o=Sippy 183797232 0 IN IP4 xxx.xxx.xxx.xxx

s=VoipCall

t=0 0

m=audio 10126 RTP/AVP 8 0 18 8 18 101

c=IN IP4 192.168.41.1

a=rtpmap:8 PCMA/8000/1

a=ptime:20

a=rtpmap:0 PCMU/8000/1

a=fmtp:18 annexb=no

a=rtpmap:18 G729/8000/1

a=rtpmap:8 PCMA/8000/1

a=fmtp:18 annexb=no

a=rtpmap:18 G729/8000/1

a=rtpmap:101 telephone-event/8000/1

a=sendrecv

 

 

IVM -> PBX:

v=0

o=NCHSoftware-IVM 1318295087 1318295092 IN IP4 192.168.41.21

s=IVM Answering Attendant Call

c=IN IP4 192.168.41.21

t=0 0

m=audio 8000 RTP/AVP 0 8 101

a=rtpmap:0 PCMU/8000

a=rtpmap:8 PCMA/8000

a=rtpmap:101 telephone-event/8000

a=fmtp:101 0-16

a=sendrecv

a=direction:active

 

Since the uplink provider asks for g711a and receives g711u, the remote end hears nothing coming from the IVM.

 

Is there any way to fix this ?