The model is simple in that it simulates only one remote institute. The remote institute is connected to CERN via a WAN ATM cloud via CISCO-type routers at each end. At the remote institute are modelled three different workstation types: one that is running simulation, one that is running analysis, and one that is running reconstruction. Bear in mind that all components of the model as shown can be replicated and grouped as necessary. This means that, once one is satisfied that the components of the simple model are being simulated correctly, then one can scale up the simulation by, for example, having twenty simulation workstations, and fifty remote institutes.
Returning to the model, the tasks that run on the workstations are modelled as step-wise sequencies. The "Reconstruct Event Remote" task, for example, consists of the following atomic steps:
The task itself can be scheduled to run in many different ways. These include the task running every so many seconds, the task running for so many events, the task running randomly according to a user-defined probability function, or the task running on reception of a message. In the model shown I chose the task to run to reconstruct 1000 events i.e. in a loop.The model, when run, can be animated and real-time graphs can be plotted of, for example, congestion on the CERN FDDI, or I/O rates to the local workstation disks. This is quite good fun to watch. In fact, building a model using this tool is entertaining, but there is a rather steep initial learning curve. The development of various "scenarios" is well supported, allowing the modeller to see the effects of, for example, a network link becoming unavailable, or the effects of an disk I/O bottleneck at CERN.