Server Redundancy

Using server redundancy, a standby server can take over the tasks of a regular server suffering from, for example, hardware failure. This way, a faulty server can be replaced with a minimum of disturbance. When using server redundancy, regular servers and an additional, standby server are grouped as a cluster. The standby server is prepared with data from the regular servers in the cluster and ready to start an instance of any of these servers in case of a server fault.

Each server in a cluster supervises the state of the other servers. In case of a server failure, the software and configuration running on the faulty server will be activated and started on the standby server. The standby server will also manage the media gateway or gateways of the faulty server. In a N+1 Server Redundancy scenario, if in the very unlikely event that there are more than one faulty server at the same time in a cluster, the standby server will only replace one of the faulty servers. Other faulty servers will not operate until the fault is fixed and they are restarted.

When a regular server recovers from a failure, an automatic or a manual fallback will take place. During fallback, the Service Node software is stopped on the standby server and is then reloaded and restarted on the regular server.

At failover, the standby server will take over the identity of the failing server and the control of the media gateways in the failing server. For ongoing TDM traffic related to the media gateways controlled by that server, all connections will be lost when the server fails. All new traffic will be redirected to the standby server. In a distributed system connected over limited bandwidth (WAN), each remote domain must have its own standby server.