In queueing theory, a discipline within the mathematical theory of probability, Kendall's notation (or sometimes Kendall notation) is the standard system used to describe and classify a queueing node. D. G. Kendall proposed describing queueing models using three factors written A/S/"c" in 1953 where A denotes the time between arrivals to the queue, S the service time distribution and "c" the number of service channels open at the node. It has since been extended to A/S/"c"/"K"/"N"/D where "K" is the capacity of the queue, "N" is the size of the population of jobs to be served, and D is the queueing discipline.