This is just a simple abstraction of a simple queue simulator. I use the word simple to clarify that it is just a simple D/D/1 case. However, deriving from this base class, a more complicated simulating case can be produced.
The base class provides with the basic implementation to track most of the relative status data, including arrival time, departure time, number in system seen by an arrival, workload and so on. Although this is not the best implementation, if you looking for material related to simulation of queueing system, it's still worth the effort to take a look.