The Gatekeeper function is used to allocate the IP address of a destination gateway to a dialed extension (IP address resolution). The Large Enterprise Gatekeeper (LEGK) performs this function using a HG 3500.

The gatekeeper functionality (LEGK) is fully integrated in the LCR function in OpenScape 4000. The LEGK is therefore neither an external server nor a host in the IP network. The LEGK is a process within the OpenScape 4000 call processing software. The Gatekeeper function is consequently fully configured using AMO commands. The Web Based Management (WBM) tool in HG 3500 is only needed for special settings, for example, codec selection and QoS. With the HG 3500 Common Gateway these features are also configurable via AMO - the WBM is now almost exclusively used for maintenance tasks.

If IP trunking is used in a purely OpenScape 4000 networked system, then all HG 3500 gateways connected must use the LEGK of their respective nodes. HG 3500s may not register with the LEGK of another node.