This Recommendation defines the operation of the Digital Subscriber Signalling System No. 2 (DSS 2) for the handling of the Look-Ahead feature that may be supported, as a network option, prior to Basic call and connection control at the TB or at the coincident SB and TB reference point of the User to Network Interface of the Broadband Integrated Services Digital Network (B-ISDN). The Look-Ahead feature defined in this Recommendation enables the network to check whether compatible user equipment are connected to a user-network interface and whether they are free or busy. This feature can be used prior to an incoming call offering at the user-network interface.