Microsoft® Lync Server 2010 Unleashed

Signaling

To facilitate users who are able to call each other, there must be some information exchanged between the PBX and the end users, such as the phone number of the caller and the phone number of the callee. This is referred to as the signaling information, and usually contains more than just phone numbers. However, for the sake of this text, it can be considered what controls the calls. The signaling information is how a call is placed, transferred, or ended. The actual voice traffic, or the audio a user speaks and hears, is considered the media.

Signaling information can come in the form of in-band or out-of-band. In-band means the information shares the same channel or line as the media. The most common form of in-band signaling is dual-tone ...