Inter-Gateway Alternate Routing (IGAR) provides an alternate inter-region routing mechanism that is used when the IP network cannot, or should not, carry bearer. IGAR preserves the internal makeup of a call, so the call’s use of non-IP bearer facilities is transparent to the end user. IGAR can be triggered by Call Access Control via Bandwidth Limitation (CAC-BL), or can be forced to use an alternate route. IGAR can use Public Switched Telephone Network (PSTN) facilities, or private switched facilities to carry the inter-region audio bearer.

After failover, if a survivable core server controls media gateways or gateways in one or more network regions where IGAR is administered, IGAR continues to work. However, if media gateways or gateways across different network regions are controlled by separate survivable core servers, calls between these systems are not seen as internal calls and therefore, IGAR does not apply.

For example, a survivable core server customer with eight media gateways administers each media gateway in a separate network region (one through eight). IGAR is administered between all eight regions. A network fragmentation failure occurs. Media gateways one through four failover to survivable core server one. Media gateways five through eight failover to Local Only survivable core servers. survivable core server one uses IGAR to establish inter-media gateway bearer between media gateways one through four. Each Local Only survivable core server controls one media gateway (five through eight). IGAR does not apply for the Local Only servers.