Control Message Signaling [Simple Telecom]

Control message signaling (commonly called “signaling”) is the process of transferring control information such as address, call supervision, or other connection information between communication equipment and other equipment or systems. There are two methods used for signaling: in-band and out-of band signaling.

In-Band Signaling
In-band signaling occurs when control messages share the same communication channel as the information signals (e.g., within the audio signal bandwidth). In-band signaling requires the users voice or data information to be momentarily interrupted or altered while signaling messages are being transferred. In-band signaling is sometimes called blank and burst signaling.

Figure below shows the process of in-band signaling. This diagram shows that a signaling message has been created to control the communications line (e.g., to transfer a call). To allow the transmission of the control message, the information is temporarily inhibited (or discarded) and the control message is sent on the same channel.


In-Band Signaling

Out-of-Band Signaling
Out-of-band signaling is a process of sending control signals outside of the communication channel that is in use (e.g., outside the audio signal frequency range). Out-of-band signaling allows uninterrupted communication while the users voice or data information is being transferred.

Figure below shows how out-of-band signaling occurs. This diagram shows that a control message can either be sent on the same channel but in different time slots than the information (e.g., voice) signal or over a separate control signaling network (called common channel signaling).


Out-of-Band Signaling