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M/M/1 Queuing System

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Overview

This example shows how to model a single-queue single-server system with a single traffic source and an infinite storage capacity. In the notation, the M stands for Markovian; M/M/1 means that the system has a Poisson arrival process, an exponential service time distribution, and one server. Queuing theory provides exact theoretical results for some performance measures of an M/M/1 queuing system and this model makes it easy to compare empirical results with the corresponding theoretical results.

Structure

The model includes the components listed below:

  • Entity Generator block: Models a Poisson arrival process by generating entities (also known as "customers" in queuing theory).

  • Simulink Function exponentialArrivalTime(): Returns data representing the interarrival times for the generated entities. The interarrival time of a Poisson arrival process is an exponential random variable.

  • Entity Queue block: Stores entities that have yet to be served in FIFO order

  • Entity Server block: Models a server whose service time has an exponential distribution.

Results and Displays

The model includes these visual ways to understand its performance:

  • Scopes labeled "Waiting Time: Theoretical" and "Waiting Time: Simulation" showing the theoretical and empirical values of the waiting time in the queue, on a single set of axes. You can use this plot to see how the empirical values evolve during the simulation and compare them with the theoretical value.

  • A scope labeled "Server Utilization" showing the utilization of the single server over the course of the simulation.

Theoretical Results

Queuing theory provides the following theoretical results for an M/M/1 queue with an arrival rate of $ \lambda $ and a service rate of $ \mu $:

  • Mean waiting time in the queue = $ 1/(\mu-\lambda) - 1/\mu $

The first term is the mean total waiting time in the combined queue-server system and the second term is the mean service time.

  • Utilization of the server = $ \lambda / \mu $

Experimenting with the Model

Move the Arrival Rate knob during the simulation and observe the change in the simulation results

Related Examples

References

[1] Kleinrock, Leonard, Queueing Systems, Volume I: Theory, New York, Wiley, 1975.

See Also

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