5.6. Benefits of Dual Resilient SIU Configurations

A dual-resilient SIU configuration brings an additional level of fault tolerance to a Global Call SS7 system. It consists of two SIUs configured as a single point code in the SS7 network. Host systems are connected via TCP/IP to both servers.

Under normal circumstances (both servers up and running) the load is shared between both units (see Section 3.3.3, ISUP Configuration). If one unit fails - either the whole unit or its communication with the hosts -, the partner unit maintains MTP operation of the node. However, telephony circuit groups that were active on the failing SIU need to be transferred to the partner SIU in order to be restored. With Global Call SS7, this procedure is performed automatically by the Intel® Dialogic SS7 server. The application will only see that circuits are blocked (GCEV_BLOCKED event is received) and then unblocked after they are successfully transferred to the partner SIU. The application should handle this as any other case of blocked circuits.

Global Call SS7 automatically handles the restoration of the circuit groups to their "preferred" SIU when it comes back up after a failure. Again, the only thing the application will notice is that circuits are blocked before they are transferred and unblocked when the transfer is complete. Because this transfer must be done for a complete circuit group, Global Call SS7 will block each circuit in the group as they become idle. Circuits that have an active call are only blocked after the call is finished. Once all circuits are blocked, the transfer to the preferred SIU is performed and circuits are then unblocked.

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