SIP proxy

(Session Initiation Protocol proxy) A server in a SIP-based IP telephony environment. It is required in large companies with numerous telephone numbers or when the Internet is the long distance transport. The SIP proxy takes over call control from the terminals and serves as a central repository for address translation (name to IP address).

The SIP proxy server provides similar functionality to a gatekeeper in an H.323 environment or a softswitch in an MGCP/MEGACO environment. SIP supports both stateless and stateful connections. A stateless connection establishes the call and then politely gets out of the way. A call stateful proxy stores all signaling events for the duration of the call. Some SIP proxy servers deposit cookies in the IP phone/terminal as a method of providing state information.