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