[rescue] Static IP! Now what?

JP Hindin jplist2008 at kiwigeek.com
Wed Apr 5 11:01:10 CDT 2017

On Wed, 5 Apr 2017, Scott Newell wrote:
> bridged DSL modems for the WAN connection before), and I'm curious about how 
> well VOIP will work for our fax line. The telco has shipped in an Adtran box

If your VoIP provider supports the T38 fax protocol then life is more than 
likely going to be fine. It won't be 100% - but T38 has a number of 
built-in protections for handling brief faults in an IP network which 
makes it considerably more robust.

T38 adoption can be spotty amongst vendors - and upstream vendors may not 
support it even in a pass-through mode, so a vendor who claims T38 
support may not guarantee a fax call goes via T38.

This being said - T30, or standard fax tones over a VoIP line, is usually 
fine, as long as you're ensuring you're using g711 as the CODEC in use. 
The other CODECs drop the high and low frequencies on the line as a matter 
of course and then compress the audio stream which often shifts the pitch 
of the tone to a point where the receiver is unable to positively identify 
it any longer.

I run the telco department on a reasonably large VoIP/telco company and we 
have an amazing amount of customers who are happy with T30 in their daily 
lives. We also have a lot that periodic failures drive them up the wall 
and they opt for a T38 fax-to-eMail/eMail-to-fax setup instead.


  - JP

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