[Asterisk-Users] T.38 support

[Darren Nickerson]

James H. Thompson jht at 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 at ifax.com
+1.215.438.4638 x8106
+1.215.243.8335 (fax)