Signalling (telecommunication)

In telecommunication, signalling (or signaling) has the following meanings:

• The use of signals for controlling communications.
• In a telecommunications network, the information exchange concerning the establishment and control of a connection and the management of the network, in contrast to user information transfer.
• The sending of a signal from the transmitting end of a circuit to inform a user at the receiving end that a message is to be sent.

In telephony, signaling is the exchange of information between involved points in the network that sets up, controls, and terminates each telephone call In in-band signaling* the signaling is on the same channel as the telephone call. In out-of-band signaling*, signaling is on separate channels dedicated for the purpose.

In-band signaling-In the public switched telephone network, (PSTN), in-band signaling is the exchange of signaling (call control) information on the same channel that the telephone call itself is using. Today, most long-distance communication uses out-of-band signaling as specified in various Signaling System 7 (SS7) standards.

Out-of-band signaling- Out-of-band signaling is telecommunication signaling (exchange of information in order to control a telephone call) that is done on a channel that is dedicated for the purpose and separate from the channels used for the telephone call. Out-of-band signaling is used in Signaling System 7 (SS7), the latest standard for the signaling that controls the world's phone calls.

Source: from Federal Standard 1037C and from MIL-STD-188

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