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

[David Backeberg]

On Fri, Mar 13, 2009 at 2:30 PM, Marshall Henderson
<marshallmch at gmail.com> wrote:
> On Fri, Mar 13, 2009 at 11:07 AM, David Backeberg <dbackeberg at gmail.com> wrote:
>> 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.
>>
>
> Do you have any specifics to share about the problems you're finding?

Sure. I can't disagree with the poster who said that problems they've
seen are really the other side's fault. But assigning blame doesn't
make me any happier. I have fax receiving problems I can't reproduce.
When I load test it, I don't have problems. When I send 'real' inbound
faxes from outside the network, over the real phone system, I don't
have problems.

I'm in New Haven, CT. One sender that messes up the most is in Kansas
City, KS. They are a legitimate client, really sending a fax. I get
occasional fax receipts that say:

'The call dropped prematurely'

There will sometimes be a cluster of these, followed by a successful receipt.

When I load tested, and send from real fax machines out and back in on
POTS, I get 100% success. I've successfully load-tested around 175
simultaneous inbound faxes. I slowed down the simulation to about 5
simultaneous faxes, and left that running over a long weekend,
generating something like 30,000 faxes and something like 1GB of
received fax files. Again, the success rate was 100%. A problem with
my simulation was that I used sending faxes that speak the protocol
correctly. Does anybody have some faxes that send garbage?

Then I put it into production with a limited amount of real fax
traffic for our clients. I'm talking fewer than 10 calls per day most
days. But it seems like the reality of the speed of light over
continental long-distance, combined with the reality of crappy fax
machines that don't speak protocols correctly result in occasional
failures. I've made some adjustments that I think anecdotally have
solved the silly problems, but that one with the faxes dropping early
is the one that (maybe) hasn't gone away.

I'd like a success rate around 99%. I'm getting around 63% if you
count individual failed calls that eventually result in a success. I
can't tell if I'm having bad luck with this phase of my pilot or if my
failure rate is going to remain constant as I add clients. I need more
data points to get statistical significance. What I really need is a
failing fax I can control, then tune parameters on my side, and see if
the failure rate gets worse or better. Seriously considering breaking
down and asking for the cooperation of the client in that endeavor.

People who have been following my posts on this topic know that I'm using:
PRI(s) -> Cisco voip gateway hardware -> T.38 / SIP / g711 ->
Asterisk-1.6 with ReceiveFax (depends on SpanDSP, but does NOT use IAX
or IAXmodem)

What I've been 'tuning' most recently have been arguments to the Cisco
setup fax and SIP translation.

I did try out IAXModem with Hylafax and 1.4 and had lots of problems
that all went away when I switched to using the approach I use now. I
never tried 1.6 with IAXModem and Hylafax, so I can't tell you how
well they work together.