Faxing over SIP with Analog Extension

[Tele-tech]

Hey there,

We have an existing NS700 that we recently switched from PRI to SIP, they had analog fax lines, and we moved those over as DID's to SIP and programmed analog extensions for the fax machine with the fax DID's pointed towards the fax lines.

An issue we are having - on outgoing faxes, we are intermittently getting a "failure notice" when sending faxes. I can call the receiving fax numbers and confirm that a fax machine is picking up on the other side. So I know the line is working and that there is a fax machine on the other end.

Since the fax machine is sending the fax through the PBX and then over the SIP lines, is there something that might be missing in programming? The SIP Ports on the gateway are sending as G711 and not as t.38, but changing that doesn't seem to affect the issue. We are not using a STUN server or NAT Traversal for the SIP server.

Thanks

 

[inlsp05]

Use g711ulaw for t38 fax .

PG4E

 

[Fodrod]

t.38 support will depend on your sip provider. I'm currently working with my sip provider to get it working properly. If i come up with some thing that's not incredibly specific to them, I may say something else here

 

[Fodrod]

Update - My observations is that it doesn't work. The pbx sends the sip re-invite to t.38, it finishes the handshake with the sip provider........... then continues to send g.711 packets.... and then the sip provider tries to switch back to g.711. However, on a mediatrix4102s, connected directly to the sip provider (and not when behind the pbx) works great. I presume any ata works fine. Panasonic support tried telling me it's the sip trunks fault, which looking at the wireshark i fail to see how that's possible.