New APOS Release to provide Gatekeeper Function. Now, gatekeeper feature is embedded into AddPac VoIP gateway in order to solve the dynamic IP changing of gateway and extremely easier configuration of a lot of gateways for main-branch offices. The gatekeeper can be configured as hot-standby relationship to solve the network or system fault on the gatekeeper. Normally, the primary gatekeeper is providing gatekeeper service to gateways and the secondary gatekeeper is in operational down status with monitoring primary gatekeeper. Whenever the primary gatekeeper become to be unavailable or abnormal, the secondary gatekeeper wake up to provide service. This feature is applied to AP1000, AP1005, AP2110, AP2120, AP2520, AP3100, AP3120, AP3220 models.