| Selected Examples |
Batch Service II
Some situations demand a somewhat different approach
to batch service; for example, consider a washing machine.
The machine is started when enough items have
arrived for service to complete the batch.
However, unlike the preceding example, all the items in
the batch finish at the same time.
The model in Figure 10.17 accomplishes this.
|
Figure 10.17: Batch Service
In this model the service distribution
in the MServer
labeled "Batch Server" is deterministic with a large parameter
value, for example, 
.
The Server labeled "Delay" provides the actual sample of
the service time for the entire batch.
The Batch Server is turned on before the Delay and
off after service for the batch is complete.
Since turning the server off does not preempt transactions
currently in service, there is another Trigger labeled "Preempt"
that preempts all the transactions in the Batch Server.
Since the transactions are preempted, they leave the server through
the balk node.
Notice the LinePlot labeled "Server Utilization," which shows the number of transactions in service over time. It demonstrates graphically the batch service and dependent nature of the service completions.
Because of the modeling technique used here, the
service time distribution is the
minimum of and 
, an exponential
random variable.
If you want the service time distribution to be , then
use caution in choosing so that the probability that
is very small and highly unlikely to occur within
the number of samples planned.
Copyright © 2008 by SAS Institute Inc., Cary, NC, USA. All rights reserved.