RE: Feature Request: Outgoing Fax |
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In addition to the pertinent information provided by bobmats' post, it should be noted that Fax over IP (FoIP) is having a unique set of issues of its' own.
• First and foremost, T.38 is not a standard. It has not been ratified as a standard in the way SIP or ISDN is, and it might never become one. As a result, there in no really strong incentive for equipment manufacturers to proceed with interoperability tests, to ensure their compliance with a non existent standard.
• For Fax over IP to work properly, every part of the fax call has to support T.38. If it doesn't, the fax transmission might fail. Although fax transmission is so commonplace in our days, its' protocol is based on a very strict set of timers intended for PSTN networks, which tend to expire often in jittery IP networks. The T.38 method has tried and somewhat succeeded to mitigate these factors, but unfortunately is not universally used.
As a result, if the trunk from your ITSP claims to support T.38, take their claim with a grain of salt. Can they guaranty that everyone of their upstream call termination providers support T.38 for FoIP too? Hardly.
A similar fate applies to DIDs. Most of the time their ITSPs don't guaranty T.38 support. So Fax over IP becomes a trial and error proposition. Try and see. No guaranties whatsoever.
However if Fax over IP is important for your operation, you should look into the dedicated services which are specializing in FoIP. They might be able to provide you with some guaranties for fax delivery, albeight at a higher price from a comparable VoIP call.
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