Simulation parameters

Metric(s) - In order to include specific overlay metrics to be collected in a simulation, they have to be specified in the simulation configuration file. Each individual metric, as depicted in Figure 4 has to be specified as a bean with a metrics class name and the bean itself has to be included in a metrics property of a simulation bean. For the list of available metrics we refer the reader to the p2pns.metrics package. Additional metrics can be added by extending p2pns.AbstractMetric class and implementing its abstract methods.

**Figure 4:** Simulation configuration file for OMNI overlay - metrics
$\begin{figure} \begin{verbatim} <beans> ... <bean id=''stress'' class=''p... ... </list> </property> ... </bean> </beans>\end{verbatim} \end{figure}$

Network topology - The network topology, as depicted in Figure 5, has to be specified using a p2pns.Graph bean and an import property of that bean has to be set to a file containing a BRITE top-down two-level topology.

**Figure 5:** Simulation configuration file for OMNI overlay - network topology
$\begin{figure} \begin{verbatim} <beans> ... <bean id=''physicalNetworkGra... ...lue>0</value></property> </bean> ... </beans>\end{verbatim} \end{figure}$

Tree-first overlay - A tree-first overlay instance has to be configured as a bean by specifying the desired class that implements a certain overlay algorithm. In the example depicted in in Figure 6, a p2pns.omni.OmniOverlay bean is created with specified properties. Various overlay algorithms are likely to have their own specific properties. However, the minimum properties that need to be specified for every overlay are: the physical network graph and the source node. In order to simulate additional tree-first overlay algorithms one would have to extend p2pns.AbstractOverlay class and implement its abstract methods.

**Figure 6:** Simulation configuration file for OMNI overlay - tree-first overlay
$\begin{figure} \begin{verbatim} <beans> <bean id=''a'' class=''p2pns.util.U... ...rlay-omni''/></property> ... </bean> </beans>\end{verbatim} \end{figure}$

Metric exporter(s) - Exporters that will collect the simulation results have to be declared as beans. Exporters specified as a metricExporter property of a simulation bean will actually be used during simulation. In the example depicted in Figure 7, only XMLExporter is used. However, the simulator can use multiple exporters simultaneously. The available exporters are located in the p2pns.exporters package. Additional exporters can be specified by implementing p2pns.MetricExporter interface.

**Figure 7:** Simulation configuration file for OMNI overlay - exporters
$\begin{figure} \begin{verbatim} <beans> .... <bean id=''xmlresult'' class... ...lt''/> </list> </property> </bean> </beans>\end{verbatim} \end{figure}$

Simulation file - A previously generated simulation file is specified as a property of a simulation bean as well. See Figure 8 for details.

**Figure 8:** Simulation configuration file for OMNI overlay - simulation file
$\begin{figure} \begin{verbatim} <beans> ... <bean id=''simulation'' class... ...k.xml</value></property> </bean> ... </beans>\end{verbatim} \end{figure}$

After all the simulation parameters have been specified, a simulation is started using the p2pns.tools.Simulator class and passing the simulation file as a parameter. For example, the OMNI simulation could be started by passing an overlay simulation configuration file depicted in Figure 3 to p2pns.tools.Simulator.

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Overview of simulation tools

p2pns.tools.Simulator