out-of-band signalling
Out-of-band signaling is a signaling system in which frequency ranges or channels outside the transmission range intended for the user data are used for signaling.
Out-of-band signaling, which also includes central channel signal ing, is used in GSM and ISDN, among others, and is used to transmit signaling data for signalling. In addition, out-band signaling is also used for error messages in order to bypass possible influences or problems on the in-band channels.
If the signaling data is transmitted in the same transmission channel as the user data, this is referred to as inner-band signaling.