While a gatekeeper is not necessary to enable communications, it provides a variety of functions to a H.323 network. If a gatekeeper is present, the standard requires that H.323 terminals register themselves with the gatekeeper controlling their network zone. This allows for people to call using friendlier names, such as an email type address. This accepts or declines a call based on a variety of criteria, including available network bandwidth or authorization.
Simple gatekeepers allow all calls through.
This is distinct from the terminal, where the end user can decide whether or not to answer a given call. The gatekeeper can accept or deny calls based on the available network bandwidth or a preset maximum number of simultaneous calls. This keeps conferencing calls from overloading the network. The gatekeeper controls all devices in its zone, and can allow devices to join and leave the zone. The gatekeeper can process the call control signals, or allow them to bypass it and go directly to the other terminal.