Here's a question that I hope T-D readers can help me with.

I have a vague memory of some requirement that VoIP phone lines support
FAX transmission. I'd like that to be true, but before I go to the
effort of getting my VoIP->POTS adapter to work with Callcentric, I'd appreciate your help.

Is VoIP capable or carrying FAX calls? Is there any requirement that
VoIP providers such as Callcentric support such a capability?

Bill
--
Bill Horne

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It appears that Bill Horne <telecomdigestsubmissions@remove-this.remove-this.telecom-digest.org> said:

Is VoIP capable or carrying FAX calls? Is there any requirement that
VoIP providers such as Callcentric support such a capability?

Why are you asking us? They have a detailed FAQ on this very question:

https://www.callcentric.com/faq/30#205

(Short answer, yes, but read the whole thing.)

R's,
John

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In theory, VOIP can carry fax transmissions, but in practice
it does not work very well. You need to be using a simple
codec (alaw or ulaw) and have very little timing jitter
in your network path... otherwise there will probably be
enough waveform distortion to corrupt the fax transmission
badly. Other types of modem-over-VoIP have similar
problems.

Some VoIP providers have the ability to detect a fax handshake
in an incoming call, terminate the call to a faxmodem, and
forward the fax to you via email... and may provide an
email-to-outbound-fax origination service as well.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Bill Horne <telecomdigestsubmissions@remove-this.remove-this.telecom-digest.org> wrote:

I have a vague memory of some requirement that VoIP phone lines support
FAX transmission. I'd like that to be true, but before I go to the
effort of getting my VoIP->POTS adapter to work with Callcentric, I'd appreciate your help.

It will be slow and unreliable to transmit fax audio through
Voice-over-IP. However, most VoIP adapters have a T.38 settings, and if
this supported by your Voice-over-IP provider, it will work [1]: the fax
will not be sent through audio but numerically:

without T.38, slow, unreliable:

fax machine --- VoIP adapter --- Internet --- VoIP provider
analog numeric audio
audio numeric audio

with T.38, fast, reliable:


fax machine --- VoIP adapter --- Internet --- VoIP provider
analog T.38 data
audio T.38 data

After the VoIP provider, you get a standard phone network capable of
handling fax audio, where T.38 is converted back. But more problems
might happen if the other end is also VoIP without T.38.

Another alternative would be to sign up with an e-mail to/from fax service provider, there the fax is sent or received as a compressed image.

[1] https://www.callcentric.com/faq/30#205
seems to support receiving fax to e-mail, and has information about
T.38 and no T.38.

--- SoupGate-Win32 v1.05
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