The gateways interfacing with the public switched telephone network (PSTN) have a limited number of ports. Therefore, other gateways have been called into service to handle the outgoing call volume, and the route lists and route groups have been re-designed so that if the first gateway is busy, the outgoing call should attempt the second gateway. Although the configuration of Cisco CallManager appears correct, the outgoing calls do not roll over to the second gateway.
When calls do not route out of the additional gateway, even though the route group is configured currectly, the likely cause is that the service parameter StopRoutingOnUserBusyFlag is set to True. Setting this parameter to False makes the route group behave as expected.