Session Border Controller. An SBC is placed in the signaling path between a VoIP caller and a callee to act as if it is the

called VoIP phone and places a second call to the called party. As a result, both the signaling traffic and the media traffic

cross the SBC. A Session Border Controller is a device used in some VoIP networks to exert control over the signaling and

usually also the media streams involved in setting up, conducting, and tearing down calls.

Within the context of VoIP, the word "Session" in Session Border Controller refers to a call. Each call consists of one or

more call signaling streams that control the call, and one or more call media streams which carry the call's audio, video,

or other data along with information concerning how that data is flowing across the network. Together, these streams

make up a session, and it is the job of a Session Border Controller to exert influence over the data streams that make up

one or more sessions.