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.