Olivier Krief wrote:
1. Does using iaxmodem imply that, for example, incoming fax calls are
processed that way ?
- PSTN calls are terminated on TDM board (Digium, Sangoma, ...)
Yes. The PSTN call terminates there and (usually) takes a short IAX2
hop over the loopback adapter to iaxmodem.
- the media flow (G711 as it comes from PSTN) is forwarded without any
modification to the right instance of iaxmodem software process
Saying "without any modification" is risky. Your Asterisk configuration
may very well modify the audio independently. The "without any
modification" part depends upon your Asterisk configuration.
- iaxmodem process are "managed" by hylafax application but are seen
and identified by Asterisk as IAX softphones (during above mentioned
registration)
Yes. Also, iaxmodem doesn't *have* to register. It's just one way of
doing it. If you have 30 iaxmodem processes all registering in the same
fraction of a second then it can get nasty.
- media is processed once, according hylafax config (that often means
forwarded to printer or email), after a single "move" from TDM board
to server processor through PCI bus
Yes, the media is processed by HylaFAX.
2. If it's correct, fax speeds and protocols (V29, G3, ...) are
defined by hylafax and iaxmodem.
So, how do hylafax-iaxmodem speeds and protocols compare with those
from a standard fax machine ?
I mean, if you had bought a new fax machine and had it connected to
the PSTN, would you get a different set of speeds and protocols ?
iaxmodem uses the spandsp library. So currently its modulation protocol
support is limited to V.27ter and V.29. Partial (sending) V.17 support
is available. V.34 (Super G3) support is not. So those are fax speeds
2400 bps through 14400 bps for sending and 2400 bps through 9600 bps for
receiving. Most new fax machines that you would purchase off-the shelf
would support either 2400-14400 or 2400-33600 depending on whether or
not it supported Super G3.
3. How do iaxmodem and rxfax-txfax DSP functions compare ? Are they
using the same library ? Is there any standard allowing iaxmodem or
rxfax-txfax to benefit from hardware DSP inside TDM board ?
iaxmodem is a modem that uses spandsp and rxfax/txfax are fax
applications that use spandsp. Apples and oranges.
txfax/rxfax are flow-chart-equivalent to iaxmodem and HylaFAX together.
There are a lot of functional and feature differences between
txfax/rxfax and iaxmodem+HylaFAX.
iaxmodem does not access hardware directly, no.
4. How would that scale ? Up to 30 Calls ? Are incoming or outgoing
faxes more demanding ? Any hardware recommended ?
You should be able to run a hundred or so iaxmodem instances with
HylaFAX on most new systems without them making a dent in the system load.
Both incoming and outgoing faxes create more load in pre-processing (in
the case of sending) or post-processing (in the case of receiving) than
they do during the fax communication itself. So the demand varies upon
your configuration. If you're going to be a lot of fax image processing
(pre or post) then I would recommend offloading that to a different
system somehow.
There are no hardware preferences for iaxmodem's sake. However, you
can't be experiencing so-called "frame slips", IRQ issues, or other
issues that affect Asterisk audio.
Lee.
_______________________________________________
--Bandwidth and Colocation provided by Easynews.com --
Asterisk-Users mailing list
To UNSUBSCRIBE or update options visit:
http://lists.digium.com/mailman/listinfo/asterisk-users
