Sometimes referred to as a call controller. In voice over Internet Protocol (VoIP) networks, a softswitch often is decomposed into a media gateway (MG) and a call agent. The call agent is the logic responsible for the registration and management of resources at the media gateway (MG) and is responsible for functions such as billing and routing. In H.323-compliant networks, the call agent is known as a gatekeeper. In Megaco-compliant networks, the term is media gateway controller (MGC). In the Session Initiation Protocol (SIP), the Call Agent registers and proxies for all endpoints in a domain, including phones as well as MGs. See also endpoint, gatekeeper, H.323, media gateway, Megaco, proxy, SIP, softswitch, and VoIP.