Re: [hylafax-users] faxing over sip

[Lee Howard <faxguy@xxxxxxxxxxxxxxxx>]

Robert Moskowitz wrote:

> Interestingly, IAXModem is enough like V.34 (It does have Steve's 
> spandsp code built-in) to work over most Internet connections (I am 
> told it does breakdown when the Net gets congested and RED kicks in on 
> the routers).


I don't really understand the correlation between IAXmodem and V.34, but 
yes, I have done a number of things with IAXmodem to try to compensate 
for VoIP issues.  However, I suspect that the vast majority of the 
compensations are due to things done in HylaFAX/HylaFAX+, namely a 
tolerant Class 1 ECM protocol.

> Also once IAXmodem incorporates this version of spanDSP, it should 
> work as well with T.38.


Well, I have considered making IAXmodem use spandsp's T.38 features 
rather than the DSP... but I haven't settled on doing that.  If t38modem 
works then I don't have any reason to do that.  Furthermore, I don't 
have any immediate motivation to develop T.38 projects right now (I've 
no customers that depend on it).

> Another piece of the puzzle is T38Modem for Hylafax.  A number of 
> people use that.  But us Trixbox people cannot as it requires kernel 
> patches to Centos :(


t38modem 1.0.0 (in the OPAL project) supports both SIP and UNIX98 ptys.  
So... if that code can ever make it out of CVS/SVN then there's no 
patching of kernels required.

> FAX is holding back large-scale movement to VoIP over classic switched 
> circuits.  Classic switch circuits are going away and except for 
> 'lifeline' will start costing more.  More people are going with GSM 
> for their only phone, and GSM CANNOT support T.30; no how/no way.
>
> T.38 will be the key piece that pulls fax over to the Internet along 
> with everything else. 


I disagree with this to some extent.  I do not doubt that fax is holding 
some people back from changing fully to VoIP.  I do not believe, 
however, that it is holding back a large-scale movement.  I have had 
enough experience with businesses and VoIP over the last few years to 
realize that to many of them the quality of their phone calls is too 
important, too valuable to concern themselves over the price 
difference.  The occassional audible jitter, the disconnections, etc... 
they aren't worth the price savings to them.

It's really not a technical problem to solve, either.  VoIP cannot 
reliably replace the PSTN in all cases.  It's not a clear "better-than" 
kind of thing here.  I think that over time you're more likely to see a 
hybridization of VoIP and PSTN instead of a clear migration.

Thanks,

Lee.


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