Recommendation ITU-T Q.3301.1 v3 (formerly Q.3321.1) specifies the rcp1 protocol, a protocol between service control entities (SCEs) in the services stratum and the policy decision physical entity (PD-PE) in the resource and admission control function block. This protocol can be used to request and commit transport resources, to retrieve address mapping information that can be used to modify application signalling, and to receive reports on transport resource usage for charging. It satisfies the requirements for information flows across the Rs reference point as specified in clause 8.1 of Recommendation ITU-T Y.2111