[cisco-voip] Route Group Distribution Algorithm and SIP

[Nathan Reeves]

Scenario as follows:
 - 2 GSM Gateways located in different offices. (2N Voiceblue Enterprise)
 - 2 SIM Cards in each gateway.
 - GSM Gateways are connected via SIP trunks.

What I want to do is setup route patterns for specific (company plan)
mobiles so that when calls are made to these numbers they head out the GSM
gateways.  I'm having issues getting a failover scenario to work with this
though.  If two calls are in progress on GSM Gateway 1, calls should be
attempted on GSM Gateway 2.  If both channels are in use on Gateway 2 then
we should push the calls out PSTN.

I've attempted to place the two Gateways in one Route group, but with two
calls on Gateway 1, calls don't proceed to Gateway 2.  From logs I'm seeing
on Gateway 1 that it's passing the following back to CUCM:

   10/19/2011 20:06:08.38 <SIP> Rejecting incomming call. Reason 11
 10/19/2011 20:06:08.39 <SIP> To: 10.10.10.1 SIP/2.0 480 Temporarily
Unavailable

I've looked into using Locations and AAR but I'm not sure I'm going to get
what I want with that setup.

Anybody have any ideas if something like this failover is possible? How does
the the Distribution algorithm work in the situation of SIP Trunks and
detection of failure / when we should proceed to the second gateway in the
RG?

Thanks

Nathan
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