IP Office uses the H.323 signaling protocol using the following architectural components:

IP telephones

H.323 service endpoint devices that support audio calls. Other types of H.323 devices can support video as part of H.323.

Gateways

Provide media translation to allow calls to be made to non-H.323 devices, for instance an analog telephone or the public network to connect with a H.323 device.

Gatekeepers

Control the call processing and security for H.323 devices.

Multipoint Connection Units (MCUs)

Control conferences by adding together media streams.

These elements form an H.323 zone which is analogous to a PABX. Each zone has a single gatekeeper to control call distribution, call control and the resource management. On power-up, IP telephones, gateways and MCUs make registration requests to a gatekeeper which then authenticates (accepts or rejects) the request to become a member of the zone. Once accepted, a telephone wishing to make a call sends a call set-up message to the gatekeeper which then determines how to route the call and will then send an alert to the called telephone, or if the call is to a non-H.323 telephone establish the call via a Gateway within the zone.