High Availability Overview

High Availability is designed to eliminate a single point of failure in a network configuration. Two systems can be configured to act as a redundant pair. One of the systems is the designated Primary system, and the other is the designated Secondary system. Typically, the Primary system is the Active system, and the Secondary system is the Standby system.

If the Primary system fails because of a network or hardware failure, the Secondary system will take over and become the new Active system.

Stateful Failover

Stateful failover is a high-availability feature that transfers states between two systems so that active calls will not be terminated during an activity switch. Stateful failover was designed to support SIP trunking applications only and should only be configured in systems using an Ethernet LAN and WAN. Other applications that require additional call state (for example, multi-line appearances for IP phones as used in Hosted PBX applications) may not work correctly upon an activity switch. An activity switch will still occur for these applications, as well as those using H.323 over TCP, but the voice or video calls may need to be re-established.

B2BUA High Availability

The B2BUA HA feature allows the calls connected through B2BUA to continue seamlessly during and after a system failover. Calls that are already established stay active during system failure. New calls can be established successfully after a system failure. This feature works with UDP and TCP protocols, assuming the remote devices support new TCP connections during a call.

This feature is enabled automatically when HA and state transfer are enabled and is supported on the