In asynchronous transfer mode (ATM), a traffic parameter defined as the maximum number of cells per second, in a burst, that the network agrees to accept and transfer for a given user network interface (UNI). Excess cells may be discarded by the ingress switch, or marked as eligible for discard. For constant bit rate (CBR) service, the PCR is the guaranteed CBR for the virtual circuit. Enforcement of the PCR enables the network to allocate sufficient resources to ensure that the quality of service (QoS) parameters are met. See also ATM, CBR, cell, QoS, traffic parameter, UNI, and virtual circuit.