Out-of-band signaling

1. Signaling that uses a portion of the channel bandwidth provided by the transmission medium, e.g. , the carrier channel, which portion is above the highest frequency used by, and is denied to, the speech or intelligence path by filters.

Note: Out-of-band signaling results in a lowered high-frequency cutoff of the effective available bandwidth.

2. Signaling via a different channel (either FDM[?] or TDM) from that used for the primary information transfer.

Contrast with common-channel signaling[?], in-band signaling[?], out-slot signaling[?].

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