In packet networks, the average rate, measured in bit per second (bps), at which a public carrier network commits to support data transfer over a virtual circuit (VC) during normal operations. During periods of low network traffic volumes, the network may allow a given user or traffic flow to exceed the CIR by a rate known as the Excess Information Rate (EIR). During periods of congestion, the network restricts the user or traffic flow to a level below CIR according to some fairness algorithm that apportions available bandwidth to all. Frame relay and Resilient Packet Ring (RPR) employ CIR mechanisms. In frame relay, the calculation of the CIR is affected by the access rate and the maximum burst size (B c ). See also access rate, bandwidth, carrier, EIR, frame relay, maximum burst size, packet, RPR, and VC.
(Committed Information Rate) In a frame relay network, the average transmission rate in bits per second (typically Kbps) for a virtual circuit. It defines the maximum rate that the network can handle under normal conditions. The CIR rate plus excess burst rate (Excess Information Rate, EIR) is either equal to or less than the speed of the access port into the network. Frame relay carriers define and package CIRs differently, and CIRs are adjusted with experience. See UNI, DLCI and frame relay.