non facility associated signalling (NFAS)

Non Facility Associated Signaling (NFAS) is a signaling protocol that is transmitted in a transmission path that is completely separate from the carrier channel.

With ISDN, one Dchannel is sufficient for signaling when several B channels are bundled. In return, the other D channels can be used for data transmission. NFAS is only possible in conjunction with a basic connection to a T1 line.