Queue, Service, and Route Modeling

Generate and destroy entities, work with entity attributes, route and delay entities, write event actions

SimEvents^® software provides a discrete-event simulation engine that manages and processes sequences of asynchronous events. Entities are abstractions of discrete items of interest. Generating, moving, and processing entities in the system causes events, such as the arrival of a packet or the departure of an airplane. In turn, these events modify the states in the system to affect system behavior.

Characterize your entity with attributes, such as a destination address, processing time, or server delay. Use SimEvents blocks to generate, queue, service, delay, and route entities.

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M/M/1 Queuing System

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.

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M/D/1 Queuing System

Model a single-queue single-server system that has a Poisson arrival process and a server with constant service time. The queue has an infinite storage capacity. In the notation, the M stands for Markovian; M/D/1 means that the system has a Poisson arrival process, a deterministic service time distribution, and one server.

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G/G/1 Queuing System and Little's Law

Model a single-queue single-server system in which the interarrival time and the service time are uniformly distributed with fixed means of 1.1 and 1, respectively. The queue has an infinite storage capacity. In the notation, the G stands for a general distribution with a known mean and variance; G/G/1 means that the system's interarrival and service times are governed by such a general distribution, and that the system has one server. You can change the variances of the uniform distributions. You can use this model to examine Little's law.

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Comparing Queuing Strategies

Have you ever been in a supermarket checkout and wondered why you are in the slowest line? This example shows how queuing systems can be modeled in SimEvents for this type of application. Two parallel versions of a simple model of a four register supermarket counter are presented - one that uses four separate queues and one with a single "serpentine" queue that feeds all registers.

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Flush Entities from a Queue-Server

Use a Discrete-Event Chart block to model a queue-server that can flush entities when it receives a message on the "FlushCmd" port.

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Server with Pause/Continue

Use a MATLAB Discrete Event System block to model a single server that can pause service. The input port IN receives entities to be served. Additionally, the system may receive sporadic pause commands on port PauseCmd. If the message received on the PauseCmd port carries data=1, the system pauses. The system reschedules service for the current entity when it receives a continue message on this port, i.e. a message that carries data=0.

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Selection Server - Select Specific Entities from Server

Use the MATLAB Discrete Event System block to write a custom N-Server from which specific entities can be selected using a key lookup. Passengers enter from the IN port of the block and are stored in the block until a message arrives at the KEY port carrying a lookup key. Upon receiving this message, the system schedules an "Iterate" event during which it can visit every entity stored in it and output the one that matches the key.

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Using Entity Priority to Sequence Departures

Use entity priority to sequence entity departures when multiple entities are available to depart. The example models an airport check-in counter where passengers arrive to be checked in. Passengers can have either First-Class, Business Class, or Economy Class reservations, modeled using entity priority values 1, 2 and 3 respectively.

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Aircraft Boarding Process Flow

Model a process for boarding of an aircraft using SimEvents.

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Queue, Service, and Route Modeling

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