User Guide > Simulation

Simulation

Running a simulation

After a complete network model has been specified including Hosts, Switches, Links and Flows (and optionally Timers), you can start a simulation. This is done by clicking the Start Simulation button in the Toolbar.

You will be presented with a dialog from where you can launch the simulation:

To start the simulation without changing any options, select the Start simulation button. This will launch the simulator and run it for the specified simulation time. While running the simulator, it is still possible to continue working with the rest of the application.

The Running time tells you how much real time the simulation has taken.

The Elapsed time tells you how far the simulated time has progressed.

Events handled is a measurement of how many topology events have been carried out. An event can be anything that is done in the system, e.g. sending an Ethernet frame from an egress port or an IP stack processing a frame.

The Dropped frames counter indicates how many frames were dropped during the simulation so far.

To abandon the simulation select the Stop simulation button. The results gathered until execution was halted will still be available for viewing.

Options

Run multiple simulations in sequence

Activating this option makes it possible to run multiple consecutive simulations in one batch and gather the total results in one database. When choosing this option, the offsets of the Tasks that produce the different IPDUs are automatically randomized between 0 and the IPDU period time. Thus, at the start of each new simulation, new randomized values for the offsets are produced. Change the Number of runs sub option to the wanted number of simulations to run.

The motivation for running several consecutive simulations in one batch is that, if the offsets are randomly chosen, the different release and arrival patterns of Tasks and Frames, that typically compete for the same hardware resources, will cause different patterns of contention for these resources and thus different queuing delays for Tasks and Frames. This will translate into the latency and jitter histograms of Frames, Datagrams and IPDUs showing an increased variance and thus also an increased likelihood of finding, for example, the worst case latency that could ever occur for a particular IPDU.

It is also possible to have random offsets when only running a single simulation. Use the Randomize IPDU offsets option to accomplish this.

Simulation time(s)

Simulation time indicates the maximum simulation time. After this point in time, no new IPDUs will be produced, however, if there are Tasks and Frames queued up in Hosts and Switches the simulation will continue until these have been processed.

Seed

Checking this box allows explicitly specifying the seed value used to initialize the internal Random Number Generator (RNG) active during a simulation. Default, the RNG typically produces different series of random numbers for each simulation. Then, if for example random task offsets are used, every new simulation will differ slightly. However, if the seed value for the RNG is specified explicitly by the user, the RNG will produce exactly the same series of random numbers for each simulation and thus also the exact same simulation and simulation results, which can be of interest in certain circumstances.

Discard tasks from result file

When running a single simulation, all tasks are stored for viewing in the results section. If disk space is sparse, use the Discard tasks from the result file option to save disk space. This option is only available for single simulations.

This option allows unplugging selected Ethernet Links during a running simulation thereby effectively hindering further Ethernet frame transmission between two device ports. It can be used in combination with IEEE 802.1CB - Frame Replication and Elimination for Reliability (FRER) - to verify that Ethernet packets in a multicast FRER flow still reach the destination Host via redundant paths, despite the fact that some Ethernet Links are deliberately disabled.

Checking the box associated with a specific Link will disable it during a simulation at a specific time. The time can either be entered explicitly be the user or marked to be selected at random in the interval from zero to the maximum specified simulation time.

When a simulation ends

When a simulation is done or when stopping the simulation manually, the simulator will start its shutdown sequence. The sequence involves emptying internal queues to get the correct statistical measurements and also some housekeeping (e.g. freeing allocated memory).