A device used to connect diverse voice-over-IP applications and systems into a single network.
The need arises from differences in the way that H.323 and SIP perform such tasks as call setup, media negotiation and call tear-down.
A session controller provides services between H.323 and SIP endpoints. In effect, this hardware/software combination operates simultaneously as an H.323 gatekeeper and SIP proxy server. In addition, it provides the SIP/H.323 interworking function that enables any-to-any connectivity between endpoints.
The H.323 gatekeeper provides address translation, and controls access to the network for H.323 endpoints. The SIP proxy provides the primary capabilities required for call-session management in a VoIP net and processes SIP requests and responses.
When calls are placed between an H.323 endpoint and an SIP user agent, logically, the session controller views a call as two call legs - an ingress leg terminating on the session controller and an egress leg that the session controller generates. The protocol used for the egress call leg is determined dynamically and is triggered by the protocol type provisioned for the remote destination.
The session controller's interworking function must support all mandatory features of SIP and H.323 and user addressing (that is, phone numbers) must be protocol-independent with common registration paradigms adhered to.
From Session controllers join H.323 and SIP, Network World Tech Update, 10/13/03.
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