Selected Examples

Servers as Resources I

There are instances in which where the system needs to schedule concurrent service from multiple servers on a single transaction. In these situations, you can think of servers as resources that are being utilized by the transactions. For example, in an auto repair facility, several mechanics (modeled as servers) can work on a single car (the transaction) at a time. The Splitter is useful for treating servers as resources and capturing concurrent use of the resources.

Figure 9.20: Servers as Resources

Figure 9.20 shows a simple model with arrivals from two sources, each sending the transactions into a queue. If the two servers are free and there is a transaction in FIFO 1, then the first transaction inserted into the queue will flow to both the servers and service will start in each. The service times in each of these is independent (unless you construct and use a service time distribution that destroys this independence). When Server 2 becomes free, it requests a transaction. If Server 1 is busy, then the request can only be honored by a transaction in the FIFO 2 queue. When Server 1 becomes free, it requests a transaction that can only be honored if Server 2 is free and there is a transaction in FIFO 1.

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