| Building a Model with Elementary Components |
Source Components
The source components are sources of transactions for the simulation network. There are two types of sources: Sampler and Transaction Pool.
| Icon | Component | Description |
 | Sampler | generates transactions with prescribed inter-arrival times |
 | Transaction Pool | a source of transactions |
The Sampler generates a transaction, and then waits
a specified time interval before generating another transaction.
The time between transactions, called the inter-arrival time,
can be a sample of a random variable (from one of several distributions),
a fixed amount, or the value of a variable read from a SAS data set.
By default, the inter-arrival time is an observation of an
exponential random variable with parameter 1.
This means that by default the Samplers follow a Poisson
arrival process.
|
Figure 3.2: The Sampler Control Panel
Figure 3.2 shows the Control Panel for the Sampler. The combo box labeled "Inter-Arrival-Time Distribution" enables you to specify the type of distribution. If you press the down arrow a list of distributions is displayed. You select the inter-arrival time distribution by selecting one of these. See Chapter 7, "Random and Exogenous Variation in the Model," for information on the choices of distributions.
The control panel also has a slider for setting the capacity of the Sampler, that is, the number of transactions that will be generated before the Sampler shuts off. The "Transaction Image" button on the control panel enables you to choose a bitmap image that would flow through the network when the simulation is being animated.
The Transaction Pool (the other source component) differs from the Sampler only in that it does not create transactions unless it receives a request for transaction message. In other ways, it is identical to the Sampler.
The following documents the logic of the source components.
Request for Transaction
A Sampler passes requests to arcs leading into it. A Transaction Pool generates a transaction and initiates its flow.
Are You Busy Message
The source components pass this request to arcs leading out of them and return their answers.
Query Message
| Keyword | Meaning |
|---|---|
| capacity | returns the capacity |
| id | the source component's unique identifier |
| on | TRUE if the source component is started, else FALSE |
| remaining | returns the number of transactions remaining to be sent |
| size | returns the number of transactions sent |
Trigger Message
| Keyword | Meaning |
|---|---|
| reset | stops the source component and resets the number of |
| transactions remaining to be sent to 1 | |
| setCapacity | sets the capacity from the transaction attribute "capacity" |
| setDistribution | sets the distribution from the transaction attribute "distribution." |
| This attribute should be a character string whose value is one | |
| of the distributions: Exponential, Gamma, Erlang, Uniform, | |
| IUniform, and Deterministic. | |
| setParameter1 | sets the first parameter in the distribution from |
| the transaction attribute "parameter1" | |
| setParameter2 | sets the second parameter in the distribution from |
| the transaction attribute "parameter2" | |
| start | starts the source component |
| stop | stops the source component |
Copyright © 2008 by SAS Institute Inc., Cary, NC, USA. All rights reserved.