This Recommendation defines the operation of the Digital Subscriber Signalling System No. 2 (DSS 2) for the handling of Call priority that may be provided, as a service provider option, for Basic call and connection control at the TB or at the coincident SB and TB reference point of the User-Network Interface of the Broadband-Integrated Services Digital Network (B-ISDN). The call priority capability defined in this Recommendation allows for preferential treatment of high priority calls during network congestions, based on the priority level allocated to the call.