[Asterisk-Users] Asterisk and Hylafax, on the same box

[Armin Schindler]

On Fri, 31 Mar 2006, Olivier Krief wrote:
> 2006/3/31, Armin Schindler <armin at melware.de>:
> 
> > Yes, this is possible of course with the Eicon Diva Server PRI (T1) card.
> > This card provides a CAPI interface where you can connect Asterisk(with
> > chan-capi) and any other CAPI based application like Hylafax.
> >
> > You can e.g. configure chan-capi to use 20 channels and the remaining
> > channels configured in Hylafax.
> > When you use a Eicon Diva Server with DSPs on board, you don't need to
> > worry
> > about CPU power, because fax-receive is done on the DIVA card.
> > So you don't need to 'bridge' something here, it just works.
> >
> > Armin
> 
> 
> Armin,
> 
> Do you mean you could dynamically share E1/T1 channels between Asterisk and
> Hylafax applications ?

Yes, CAPI provides all available controllers (ports) and its channels to 
every application at the same time.

> For example, for each incoming call to a given fax number, Capi driver would
> trigger Hylafax software to process incoming fax and at the same time,
> Asterisk software would be smart enough to use other channels for outgoing
> calls ?

Yes, via the CAPI interface you don't reference a real b-channel, this is 
done by the driver of the ISDN card which provides the CAPI interface.

Using CAPI, the applications can (and have to) decide which calls they want 
to get signaled or which are ignored when they are meant for another 
service. E.g. the following example is not possible with CAPI:
You have one number (and the same BC) for two services assigned. If you are 
using one application, which can switch to another server by some rule, then 
it is okay. But two applications must be configured to serve the own 
numbers/services only.
Another thing is, the application does not know about busy channels. This 
means if you have a 23 channel line and 10 lines are busy with hylafax at 
the moment, then chan-capi (or another application) can use 13 channels 
only, of course. So if you have configured chan-capi with e.g. 15 channels 
to use, chan-capi will just return 'busy : no circuit/channel available'.
But this is all configuration stuff and when configured correctly, it works 
very good.

There are even more capabilities. For example Eicon is doing a lot. Their 
Diva Server cards do provide a RTP interface via CAPI (new chan-capi will 
support this). Which means coding and anti-jitterbuffer is done on the ISDN 
card, chan-capi just 'pushes' the RTP packets onto the card...

With rcapid and a patched version of the libcapi.so, you can even have the 
ISDN hardware on one server and the applications on other servers connected 
via CAPIoverTCP (bintec protocol in that case).
I use this because my faxing application (just the capifaxrecvd) runs on my 
local maschine instead of the ISDN/Asterisk/Gateway server.
 
> If this understanding is correct, what is the downside ?
> Why don't everybody use chan-capi ?

CAPI comes originally from the Windows world, but is a common ISDN API 
standard www.capi.org. So if there would be CAPI drivers for all of these 
ISDN cards, you can use CAPI (chan-capi).
So the missing part is the card-driver. Currently I know of three CAPI based 
hardware:
1) Eicon Diva Server (all cards including analog ports) with full CAPI 2.0 
   and VoIP/T.38 extensions.
2) AVM (basic CAPI 2.0)
3) mISDN driver for passive cards (hscx/hfc/...)
   and on BSD with i4b!



Armin

(www.chan-capi.org ;-)