[Asterisk-Users] GSM gateway flooded cell - how to detect?

[Colin Anderson]

We are using an Ateus VoiceBlue to GSM gateway calls on our * 1.0.9 server.
It works perfectly fine, except at peak periods, say, 10 AM and 3 PM. At
that point, calls get dropped (not gateway'd) and Asterisk jumps to the next
priority in the dialplan. Our interpretation of this is that the local GSM
cell is flooded with other calls and can't service our request, so nothing
to to with Asterisk or the gateway. No matter how hard we try, during
off-hours, we can't replicate this behavior. My question is how to detect
this behavior and relay the call out to our PRI instead. I've had a couple
of ideas so far, but nothing has panned out:

1. Use the ${DIALSTATUS} variable, however when the condition occurs, the
variable is set to NOANSWER which is the same setting if the guy doesn't
pick up his phone, so it does me no good, since I can't correctly detect
whether it is the gateway or whatever. Maybe an AGI which sets a timer to
detect ringtime? More information: This is different than if the gateway is
full and can't service the request, which I am already successfully testing
for before the dialplan makes the determination to use the gateway in the
first place or not.

2. Dial the target cell using the gateway and the PRI simultaneously, so
this masks the condition. If the gateway kacks, then the call would still go
through the PRI to the target cell.  This would work, however I am using the
'r' option to dial, in order to detect early audio if the user has his cell
off to advance the dialplan. When I do this, and the user answers, the PRI
channel gets an early-audio indicator from the GSM provider ("The person you
are calling can't answer blablabla" ), and Asterisk drops to the next
priority in the dialplan, which I do *not* want to do, until the user has
hung up or doesn't answer. Getting rid of the 'r' option is not in the
cards. 

Another idea which just occured to me is to physically move the gateway to
another location a few km away that we have a VPN tunnel to, and just route
calls over there - another cell, maybe not so saturated, right? The danger
there is that the gateway is not on the LAN so the side effect is that our
infrastructure becomes more fragile i.e. if the VPN is down the gateway
doesn't work. Still, I think it's worth a try.

Anybody have any spitballs about how to work around this issue? When the
gateway works, it saves is $2-4K a month in airtime, so I definitely don't
want to abandon it. My GSM provider (Rogers) could care less about working
with me to address this, since it is more revenue for him. 

tia