Unfortunately, we have battled Fax-over-IP issues for the better part of 8 years now as a service provider. We have tried everything, from T.38 to special ATA adapters from Commetrex / NetGen Communications. Nothing we tried worked reliably, and we could never approach 100% reliability of Fax transmissions over IP. The support burden this caused was tremendous — having to dig through endless packet captures trying to diagnose T.38 and G.711 fallback Fax issues was more than we were willing to bear.
We decided to abandon Fax-over-IP altogether and eliminate our support burden. We rolled out 2 products: a traditional Fax-to-Email offering and a product called SimpleFax which is a special ATA (the AudioCodes MP202 HTTPS variant) which takes Fax transmissions, grabs the image files, sends them as HTTPS to our servers, and we then send these out over traditional PRI lines (no IP communications involved). Since we deployed these solutions, we haven’t had an issue with Fax transmissions, and our support burden of trying to diagnose and fix Fax-over-IP-related issues completely went away.
As such, our “official response” to customers wanting to use voice DIDs for Faxing is the following:
Our underlying carriers claim that our DIDs support T.38 for inbound Fax delivery. You are more than welcome to test and use these Standard and Enhanced DIDs for Faxing if that works for you. The bulk of our termination providers claim to support T.38 for outbound Fax delivery in the US and Canada. Given that we cannot always determine the complete end-to-end path of an outbound call, we cannot say for certain whether T.38 will be honored end-to-end. If there is a carrier at the far end of the line that won’t honor the T.38, it will fallback to G.711, which could impact the reliability of the Fax-over-IP transmission. If all of this works for you, great. If you run into issues with Fax transmissions, inbound or outbound, unfortunately our support team is unable to help diagnose any such Fax-over-IP-related issues.
We highly recommend deploying our Fax-to-Email service or SimpleFAX ATA adapter for 100% reliable Faxing that is not done over IP. We simply don’t have the support resources to dig into Fax-over-IP issues which is why we deployed these 100% reliable Faxing offerings to meet the needs of our customers.