This Recommendation defines the operation of the Digital Subscriber Signalling System No. 1 (DSS 1) for the support of the Reverse Charging (REV) Supplementary service at the T or the coincident S and T reference point of the User to Network Interface of the Integrated Services Digital Network (ISDN). The Reverse Charging supplementary service allows the served user, on a per-call basis, to request at call establishment time or during active phase of the call or at the call clearing, that charging be applied to the called user, or, on a subscription basis, to be charged for all incoming calls