Page "Session border controller" Paragraph 35

In many cases, in order to hide the network topology and protect the service provider or enterprise packet network, the SBC will terminate a received call and initiate a second call leg to the destination party.

In technical terms, when used within the SIP protocol, this is defined as being a back-to-back user agent ( B2BUA ).

The effect of this behavior is that not only the signaling traffic, but also the media traffic ( voice, video ) can be controlled by the SBC.

In cases where the SBC does not have the capability to provide media services on board, SBCs are also able to redirect media traffic to a different element elsewhere in the network, for recording, generation of music-on-hold, or other media-related purposes.

Conversely, without an SBC, the media traffic travels directly between the VoIP phones, without the in-network call signaling elements having control over their path.