T.38 fax support for VoIP unlock customers

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T.38 fax support for VoIP unlock customers

Postby koreyb » 04/27/2019

Hi there,

I have a unlocked VoIP freephoneline.ca number.

I use a VoIP adapter sharing a voice line with a fax machine

In the last few months, I've noticed outgoing fax calls fail, while incoming works fine. I'm assuming it's a codec used for outgoing calls that isn't compatible with t.38 fax. In testing with another service, it works fine both ways. I get this is likely not supported but could any confirmation be given that outgoing is no longer using the ulaw/alaw codec or is this something that can be changed on the server end?
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Re: T.38 fax support for VoIP unlock customers

Postby Liptonbrisk » 04/29/2019

T.38 fax protocol works, unofficially (insofar as customer support will not provide technical support for that feature), for outgoing faxes with Obihai OBi200/OBi202 ATAs and Freephoneline.
Refer to pages 31 and 32 of the PDF guide located at viewtopic.php?f=15&t=18805#p73839. Also refer to point #4 on page 2 and also to page 45; bad jitter and packet loss can cause issues.
Even if you don't own an Obihai 200 or 300 series ATA, that general information is worthwhile reading.

You can test by faxing to a Fongo Mobile number.

I have no issues using T.38 fax protocol with Freephoneline.
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