The SCCP layer can operate in a two-board redundant primary or backup configuration in addition to the single-board standalone configuration. The boards can be in the same chassis or they can be in two chassis.
The objective of the redundant configuration is to maintain the SCCP service if any of the following scenarios occur:
The primary board fails (hardware or software failure)
The chassis containing the primary board fails (dual-node configuration)
A planned outage for maintenance purposes
Sufficient state information regarding the primary SCCP layer must be reflected in the backup SCCP layer so that operation can continue without a service disruption. This state information includes the status of remote signaling points and subsystems, the status of local subsystems, and the state of any active class 2 or class 3 connections.
The SCCP layer automatically maintains the correct state of its backup by checkpointing state information whenever necessary, such as when the state of a remote signaling point or subsystem changes or when a new connection is established (confirmed). It also restores the current state to the backup whenever the backup is reloaded or recovers from isolation. These operations are transparent to the application.