Re: Hylafax without modems - SIP?

On 01/27/2016 01:44 AM, Gary Stainburn wrote: On Wednesday 27 January 
2016 01:14:35 Lee Howard wrote:
>
> I have three Mitel 3300 controllers, one at each of my main sites, and all 3
> set up for resilience. Sorry I don't know too much about the internals of
> Mitel kit to give too much technical details.
>
> Each controller is connected to an ISDN30 which handles 99% of all incoming
> and outgoing calls.  I have a small number of PSTN lines for hisorical
> reasons and RedCare alarm lines etc.  These PSTN lines will of course have to
> stay with modems.

Okay, so the design is such that the SIP traffic is only between the Pis 
and the controllers... all of which is under your domain.  After the 
controller it's all on the PSTN.

So, you could get away with it having only minimal packet loss if you do 
everything you can to prevent collisions and congestion.  If the Pi has 
two network interfaces you could put one on the LAN and the other as a 
direct cross-over connection to the controller.  I've heard reports of 
some packet loss occurring even on a crossover connection, but as I 
don't use such I can't give any first-hand evidence.

> Lots of sites seem to refer to using Asterisk VOIP PBX software, and using
> iaxmodem.  Is this something I should be investigating, or would this just
> muddy the waters?

The sites that are doing that reliably are probably not running the VoIP 
channels (SIP or IAX2) over the network - and especially not the 
internet.  Generally those sites are using iaxmodem to communicate over 
the loopback device to Asterisk - and then Asterisk has DAHDI-compatible 
PSTN interfaces from there.

I've seen a very few reliable HylaFAX+IAXmodem+Asterisk installations 
which use SIP to connect to a VoIP provider. Generally they have a 
rather unique network proximity to the VoIP provider.

In such situations T.38 should really be the way to go. Unfortunately, 
the T.38 options for HylaFAX are frustratingly limited.  t38modem is not 
maintained well and finicky about the T.38 gateway.  Asterisk has a T.38 
stack on it's own, but it does not provide ptys.  FreeSWITCH does 
provide ptys for HylaFAX to use - and it has its own T.38 stack, but 
I've not really used it... primarily because the various tests that I've 
run with a few T.38 SIP providers over the years really never turned out 
very well for me.

Thanks,

Lee.


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