Issue with Fax Module?

Hi there!

We’re trying to get inbound faxes properly working. Not too sure what information may be helpful to post.

I’ve set up an “Incoming FAX” user, with an extension. Set up a DID to point to that extension. I enabled fax and an email for that user. I’ve fiddled with Fax Configurations. Finally - we can receive an inbound fax.

The problem is that we only receive the first page.

Any areas I should look? Is this an obvious issue for folks that don’t know faxing technology? Need a bit of help here.

Fax over SIP does not work very well. It is old technology from the 70s, which cannot handle delays. If you just need incoming fax capabilities ask your SIP-trunk provider about a fax2email solution.

Fax over VOIP is problematic using T30, So T38 was developed in which the SIP connection renegotiates a UDPTL session to carry the datagrams, it needs a competent T38 aware carrier, but generally is easily as reliable as a T30 over analog line fax and far superior to T30 over SIP. (In our case, using T38modem and a good VSP 98% plus)

Given that connection, hylafax can provide you with your fax2email/email2fax solution outside of FreePBX.

T30 over ULAW actually works quite well to the pbx on a good connection and direct audio to the carrier. All of our inbound/outbound fax traffic to the carrier is ULAW. We do T38 gateway to the ATA’s since the end user internet connection is typically unstable. The problem is most T38 carriers don’t do error correction like level3 but if we force it ULAW we get proper error correction on the carrier side and can then gateway it to T38 on ata’s which is perfect for when the end user has 33K fax machines and can’t easily be turned down to 14,400.

I would reccomend trying to set T38 to no, on sip settings and on the trunks. Some outbound carriers don’t like to honor that like intellepeer, and others. So we avoid those who try to force us to T38 even when we say no. Fax Settings 14400-9600 Error Correction on. This also avoids a T38 Reinvite incase you are double natted which outbound faxes don’t like too much on T38. If you are still using chansip it is t38pt_udptl =no.

If you are using T38 make sure your UDPTL ports are open. Not to be confused with RTP ports. They are different.

Another issue with T38 besides the lack of error correction on some carriers is the T38reinvite is supposed to be the callee only. Some carriers negotiate both which asterisk used to do until recent updates and can cause a T38 Flare. Then you have issues with the reinvite coming too late…etc. Best to use ULAW if you are doing fax to email and have QOS setup properly with dedicated bandwidth for voip. T30 fax can’t handle much jitter or packetloss, a little jitter works fine though. I’m actually undecided about using jitterbuffers. It might help or could hurt. We use fixed jitter buffers on all the ATAs. PJSIP doesn’t have jitterbuffer support though so you’d have to use chansip but I’m not sure if anyone has dug that much into fax to figure out if T30 using fixed jitterbuffers helps or hurts.

Anyways like in the last post. If you try the T38 route. Open UDPTL/T38 Ports. Make sure you aren’t double natted. T38 worked well for us for a long time but no error correction support. The carriers that do provide it, I wonder if they are just gatewaying the T30 traffic. I mean of course they are. So that’s what I’m doing.

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