[asterisk-users] Ast/Hyla/IAX Scalability?

[David Backeberg]

On Fri, Mar 13, 2009 at 11:38 AM, Marshall Henderson
<marshallmch at gmail.com> wrote:
> I recently read the thread entitled "Faxing Success Rate on PRI" which dealt
> with Asterisk/HylaFax/IAXmodem. I'm successfully using this 'recipe' in a
> few instances on systems with only a couple of analog lines all the way up
> to a full PRI worth of Iaxmodems.

Then you have probably seen that YMMD, and that some people claim
great success with VoIP fax.

Other people claim that the only way to go is a hardware fax solution,
like the dedicated multi-modem fax cards.

The only way you're going to find a solution that will work for you is
to try it, scale it, build your own expertise with your solution, load
test it, and watch your error rate.

The other consideration is your budget and your cost of dropping a
fax. The faxmodem cards are not cheap compared to a voip solution. But
if the faxes have a high value to the business the hardware cards are
probably justified.

Again, you'll find people arguing that their voip solution has as low
of a failure rate as a hardware solution. I'm jealous. My voip fax
solution does not yet have that low of a failure rate, but I'm
hopefully getting closer to working out the last bugs.

> I've also noticed that IAXmodem is compiled statically against a version of
> spandsp included with the iaxmodem source. For a large installation, would
> it be better to compile iaxmodem dynamically to reduce the per-instance size
> of each iaxmodem? Or, would it be better to simply throw more RAM at it?

I'm not sure what difference RAM makes. What breaks a fax on voip is
latency and dropped packets.

You solve both of those problems if you go the hardware solution route
with a faxmodem card.

The in-between solution is using a proprietary telco -> fax gateway,
like a Cisco box that terminates a PRI and provides FXO ports that you
plug into a single-pair faxmodem or a 'real' fax machine. That
solution quickly becomes ridiculous when you try to scale it.

> Are there any concurrency issues when receiving a large number of faxes on a
> system using IAXmodems?

File system contention, but fax files aren't very large, and I would
call that a non-issue. Most people don't want a piece of paper; they
want a PDF that they can turn into paper once in a while.