[Asterisk-Users] T.38 support

Darren Nickerson
2004-11-29T16:51:49Z

James H. Thompson jht@lj.net wrote:

> T.38 is often put forward as the solution for reliable FAX over VOIP.

With good reason ;-)

> Just wondering for anyone using T.38 (with any equipment), how well does
> it work as compared to a FAX PSTN call?

Our experience is that it's only as good as the T.30 implementation in your
T.38 gateway, softswitch etc. Since it's really them having a conversation
with the remote device, you're relying on their implementation of the fax
protocol. We recently had a problem with a customer's T.38 termination
service ... they had disabled  ECM (Error Correction Mode) as a general
policy across their devices, and as a result a lot of our customer' faxes
were of degraded quality. The provider claimed that when their network
started to drop packets, ECM caused the faxes to take too long to send
because of all image data retransmits. Our response - fix your network!

I guess that's all just another way of saying 'it depends' ;-)

One thing to be aware of when deciding between T.38 and the PSTN is that
V.34 fax (speeds above 14,400) aren't possible, so you'll want to make
sure
that the money you save from (presumably cheaper) T.38 termination is
greater than the money you save from spending less time on the wire. The
speed boost from V.34 is larger for multi-page faxes than single-pagers, and
penetration of V.34-capable machines varies from country to country and
vertical market to vertical market.

-Darren

--
Darren Nickerson
Senior Sales & Support Engineer
iFAX Solutions, Inc. www.ifax.com
darren.nickerson@ifax.com
+1.215.438.4638 x8106
+1.215.243.8335 (fax)