In the case of primary path failure due to single SBC failure, the IAD is provisioned to automatically use the alternative path.
Figure : Call Termination with Primary Path Failure
- The IAD registers with AS1 through SBC-3.
- Subscriber is pre-assigned (based on Application Server subscriber data configuration) to AS1, thus SBC10 has preset routing for the subscriber to AS1.
- From the register, AS1 is informed that the subscriber is reached by SBC-3.
- The SBC-3 goes down and AS1 can not terminate the call to the subscriber until the subscriber re-registers.
- The subscriber identifies that the SBC-3 is down only when it sends traffic (invite, refresh register etc).
- IAD chooses an alternate IP address based on the DNS resolution and opens up a new path to the AS (paths should ideally be geo redundant).
- When AS1 receives the terminating call it learns SBC-3 is unavailable and utilizes SBC-5 path. Hence IAD receives call despite failure of primary path.