Definitions for "Out-of-band signaling"
The signals used to operate the communications channel are separate from the user's data channel. ISDN uses out-of-band signaling via the D channel.
Signaling transmismitted using frequencies or channels outside the frequencies or channels normally used for information transfer. Out-of-band signaling often is used for error reporting in situations in which in-band signaling can be affected by whatever problems the network might be experiencing. (source)
Information about the state of a network or device carried outside the normal data paths using a separate channel, often a serial line, i.e., allowing a LAN device to report a malfunction or linebreak. See In-band signaling.