Re: [hylafax-users] how is vgetty implemented these days?

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Luke McKee wrote:

> Wouldn't it be great if IAX modem could RE-INVITE or use NSE to
> convert the connection to use T.38 if the remote gateway supported
> that protocol?


There is no T.38 support within the short-sighted IAX2 specification.  I 
(or someone) would need to extend the IAX2 spec to do it, and I think 
that time would be better invested in getting a SIP-using T.38 softmodem 
instead.  IAX has its purposes, but it has many limitations, as well.  
It was easy to develop with, but in the end the protocol is really not 
being further-developed by anyone.

> I read your comments on the FAQ about T.38. Now that spandsp is
> supporting T.38 will you add support to IAXmodem too?


I had considered writing a SIP-using T.38 softmodem or a 
HylaFAX-specific SIP/T.38 "ClassT38Modem" driver, but none of my 
customers are looking for T.38 technology, and so there's very little 
motivation for me.  Furthermore, other people with more experience are 
getting that very same thing done, and I'm more likely to assist them 
when I do have a need for it.

> As for V.34 support it's best implemented in hardware.


Well, you could do it in software if you really wanted.  I'm not sure 
how much CPU you'd need to allocate to it to make sure it got done 
timely.  The problem for open-source projects and V.34 is patents.

> I know capi4hylfax has got references to V.34
> in changelog
> "    * set minimum of 4800 for V.34 primary rate renegotiations (02 
> Apr 2006)
>    * improve handling of V.34 control channel retrain (02 Apr 2006)"
>
> So the code is already in the public domain for doing V.34 in a
> softdsp.


I don't know much about CAPI4HylaFAX or other things - I would suspect 
that the V.34 modulate/demodulate routines are in hardware/firmware, but 
I don't know that for-sure.

> It would be nice to get it implemented in spandsp too!
> Capi4hylafax pays it's licensing fees because it's intended to works
> with Fritz hardware. Would there be patent issues putting it into
> spandsp?


Yes, there are patent issues with V.34.  Again, I would not suspect that 
the patented V.34 routines are in CAPI4HylaFAX, but rather in the AVM 
hardware/firmware itself.  But that's purely a guess.

Lee.


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