With the ATM Block Transfer with Delayed Transmission \mbox{(ABT/DT)} capability, the amount of bandwidth allocated to the different cell flows of a connection (namely the CLP=0+1 and possibly the OAM cell flows) is constant over an ATM block and then referred to as block cell rate (BCR). Successive BCR values are dynamically negotiated between the user and the network via the exchange of Resource Management cells. The BCR negotiation for a given ATM block may be initiated either by the source or the destination. As a basic principle, before transmitting an ATM block, the source should receive an explicit authorization from the network. This paper gives the existence proof of a protocol for supporting the ABT/DT capability as specified in the May 1996 version of ITU-T Recommendation I.371.