With Facility Associated Signaling (FAS), an ISDN-PRI T1/E1 interface D-channel can carry signaling information for all the bearer (B) channels on its associated spans.
With Non-Facility Associated Signaling (NFAS), an ISDN-PRI T1/E1 interface D-channel can carry signaling information for up to 300 bearer (B) channels on its associated spans. In other words, a single D-channel can carry signaling information for numerous B-channels that are located on different DS1 media modules.
Note:
NFAS is valid for T1/E1 Country Protocol 1 only. Digital T1 service is also sometimes called DS1 to distinguish the service from analog T1 service.
ISDN-BRI trunks do not support NFAS. For more information, see, ISDN Service.
