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The generic cell rate algorithm is a leaky bucket-type scheduling algorithm for the network scheduler that is used in Asynchronous Transfer Mode networks. It is used to measure the timing of cells on virtual channels and or Virtual Paths against bandwidth and jitter limits contained in a traffic contract for the VC or VP to which the cells belong. Cells that do not conform to the limits given by the traffic contract may then be re-timed in traffic shaping, or may be dropped or reduced in priority in traffic policing. Nonconforming cells that are reduced in priority may then be dropped, in preference to higher priority cells, by downstream components in the network that are experiencing congestion. Alternatively they may reach their destination if there is enough capacity for them, despite them being excess cells as far as the contract is concerned: see priority control.
The GCRA is given as the reference for checking the traffic on connections in the network, i.e. usage/network parameter control at user–network interfaces or inter-network interfaces or network-network interfaces . It is also given as the reference for the timing of cells transmitted onto an ATM network by a network interface card in a host, i.e. on the user side of the UNI . This ensures that cells are not then discarded by UPC/NCP in the network, i.e. on the network side of the UNI. However, as the GCRA is only given as a reference, the network providers and users may use any other algorithm that gives the same result.