MATLAB SIMEVENTS RELEASE NOTES Betriebsanweisung PDF herunterladen (Seite 82)

4 Basic Queues and Servers

4-4

Servers in SimEvents Models

In this section...

“Behavior and Features of Servers” on page 4-4

“What Servers Represent” on page 4-4

“Access Server Blocks” on page 4-5

Behavior and Features of Servers

In a discrete-event simulation, a server stores entities for some length of time, called

the service time, and then attempts to output the entity. During the service period, the

block is said to be serving the entity that it stores. An everyday example of a server is a

person (a bank teller, a retail cashier, etc.) with whom you perform a transaction with a

projected duration.

The service time for each entity is computed when it arrives, which contrasts with the

inherent unknowability of the storage time for entities in queues. If the next block does

not accept the arrival of an entity that has completed its service, however, then the

server is forced to hold the entity longer.

Distinguishing features of different servers include

• The number of entities it can serve simultaneously, which could be finite or infinite

• Characteristics of, or the method of computing, the service times of arriving entities

• Whether the server permits certain arriving entities to preempt entities that are

already stored in the server

Tip In the absence of preemption, a finite-capacity server does not accept new arrivals

when it is already full. You can place a queue before each finite-capacity server,

establishing a place for entities to stay while they are waiting for the server to accept

them. Otherwise, the waiting entities might be stored in various different locations in the

model and the situation might be more difficult for you to predict or analyze.

What Servers Represent

In some cases, a server in a model is similar to an analogous aspect of the real-world

system being modeled. For example, you might use a server to represent

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MATLAB SIMEVENTS RELEASE NOTES Betriebsanweisung Seite 82