Call Termination with Primary Path Failure

Scenario

In the case of primary path failure due to single SBC failure, the IAD is provisioned to automatically use the alternative path.

Background Information

• Refer to the background information in Basic Service Availability - DNS.

Description

Figure 1: Call Termination with Primary Path Failure

1. The IAD registers with AS1 through SBC-3.
2. Subscriber is pre-assigned (based on Application Server subscriber data configuration) to AS1, thus SBC10 has preset routing for the subscriber to AS1.
3. From the register, AS1 is informed that the subscriber is reached by SBC-3.
4. The SBC-3 goes down and AS1 can not terminate the call to the subscriber until the subscriber re-registers.
5. The subscriber identifies that the SBC-3 is down only when it sends traffic (invite, refresh register etc).
6. 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).
7. 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.