Inbound Fax issues

[DavidA]

Hello,

We are running a fully updated v15.5 under Hyper-V with significant resources dedicated to the instance. We have inbound faxing setup using a trunk separate from our voice trunks. We chose a provider that appeared to have good support for faxing. I frequently get user complaints with faxes that are missing pages or parts of pages. I have the 711 fallback selected. There are just not many dials to work with to adjust this. Are there other things i could do that might help?

Thank you

 

[cobaltit]

So step one would be to look at the logs (verbose needed) or wireshark to confirm if the faxes are coming in via T.38 or G.711.

 

[eddv123]

Unfortunately there are no formal troubleshooting steps for Fax over IP (FoIP) and so many areas where it can go wrong. I have highlighted some things you may want to consider for both T.38 and G.711:

* In the case of T.38 has your provider definitely confirmed they support this method, some do not. If not then you could be using G.711 as primary - this method uses a lot of bandwidth and if you do not have a high bandwidth environment (or not using QoS on your network) then it could explain the issue.

* Are you (on 3CX) and does your provider support G.711 on the trunk side, some may only use a compressed codec such as G.729.

* Are you fully aware of the path which the FAX is taking, delays caused by IP to PSTN conversion can also cause such issues, also some gateways may not support G711 (if the fax is using this protocol).

* The switch over from voice to T.38 fax (during initial setup) can cause a lot of issues (Late Re-Invite to switch to T.38) this can be caused by a delay and again is down to network setup/QoS and fax path.

You could always get some test trunks (some you can find online as free trial) from another provider who supports T.38 and see if you get the same result(s).

Obviously as @cobaltit has said a Wireshark trace would be of good to look at if you can get one.