Inbound Fax - 3CX to ATA: 488 Not Acceptable Here

[0xDECAFBAD]

I'm unable to receive inbound faxes. I was able to send one outbound fax. When I do a packet capture on the 3CX, I see the 3CX send a SIP invite to the Patton ATA. The Patton sends a SIP invite back to the 3CX. It looks like it's trying to switch over to T.38. The 3CX then sends a Status 488 Not Acceptable Here. In the 3CX under FXS/DECT for the device I have fax transmission mode set to Fax in T.38. I see the 3CX lists fax support as not supported for Flowroute. Why is that? Flowroute supports T.38. If I look at packet captures, here is what I see for SIP Invite behavior. 3CX doesn't attempt to switch the conversation with Flowroute over to T.38. It just tells the ATA it cannot be done. With an incoming call is the SIP provider supposed to signal T.38? Or should the ATA ask 3CX to switch to T.38 and then 3CX asks Flowroute to switch to T.38? I'm not sure how the SIP conversation is supposed to go.

Outbound Faxes (working):
ATA -> 3CX (PCMA/PCMU/G729)
3CX -> Flowroute (PCMA/PCMU/G729)
ATA -> 3CX (T.38)
3CX -> Flowroute (T.38)

Inbound Faxes (not working):
Flowroute -> 3CX (G729)
3CX -> ATA (PCMU, PCMA, G722, GSM, G729)
ATA -> 3CX (T.38)
3CX -> ATA (488 Not Acceptable Here)

 

[leejor]

There are a number of posts, on the site, relating to Flowroute and faxing...

https://www.3cx.com/community/threads/t-38-faxing-does-not-work.64962/

 

[eddv123]

If not solved already, my 2 pence:

488 not accepted here as a response generally is a codec mis-match between both legs of the call.

However in FAX the only supported codec for FAX is G711 - it looks to me like you are trying to us G729 which will fail ( G729 is a compressed codec) probably best to switch to T.38 if supported by the providers and try again.

 

[0xDECAFBAD]

I ended up setting up another SIP trunk through T38Fax.com since it sounds like people aren't having luck with Flowroute even though they support T.38.