In queueing theory
, Kendall's notation
(or sometimes Kendall notation
) is the standard system used to describe and classify the queueing model
that a queueing system corresponds to. First suggested by D. G. Kendall
as a 3 factor A/B/C
notation system for chacterising queues
, it has since been extended to include up to 6 different factors.
The notation now appears in most standard reference work about queueing theory. e.g.
- A queue is described in shorthand notation by A/B/C/K/N/D or the more concise A/B/C. In this concise version, it is assumed K = ∞, N = ∞ and D = FIFO.
A: The arrival process
A code describing the arrival process. The codes used are:
B: The service time distribution
This gives the distribution of time of the service of a customer. Some common notations are:
|| Exponential service time. |
|| Degenerate distribution
|| A deterministic or fixed service time. |
|| Erlang distribution
|| An Erlang distribution with k as the shape parameter. |
|| General distribution
|| Although G usually refers to independent arrivals, some authors prefer to use GI to be explicit. |
|| Phase-type distribution
|| Some of the above distributions are special cases of the phase-type, often used in place of a general distribution. |
C: The number of servers
The number of service channels (or servers).
K: The number of places in the system
The capacity of the system, or the maximum number of customers allowed in the system including those in service. When the number is at this maximum, further arrivals are turned away. If this number is omitted, the capacity is assumed to be unlimited, or infinite.
- Note: This is sometimes denoted C+k where k is the buffer size, the number of places in the queue above the number of servers C.
N: The calling population
The size of calling source. The size of the population from which the customers come. A small population will significantly affect the effective arrival rate
, because, as more jobs queue up, there are fewer left available to arrive into the system. If this number is omitted, the population is assumed to be unlimited, or infinite.
D: The queue's discipline
The Service Discipline or Priority order that jobs in the queue, or waiting line, are served:
|| First In First Out/First Come First Served
|| The customers are served in the order they arrived in. |
|| Last in First Out/Last Come First Served
|| The customers are served in the reverse order to the order they arrived in. |
|| Service In Random Order
|| The customers are served in a random order with no regard to arrival order. |
|| Priority service
|| Priority service, including preemptive and non-preemptive. (see Priority queue) |
|| Processor Sharing
- Note: An alternative notation practice is to record the queue discipline before the population and system capacity, with or without enclosing parenthesis. This does not normally cause confusion because the notation is different.
- A Google search gives many others.