In co-simulation, each subsystem is modeled and simulated in the appropriate simulation program, potentially on different computers, and intermediate results are communicated over the network during execution time. There are two different co-simulation coupling strategies \cite{Tr_ka_2009}:

• Quasi-dynamic coupling, also called loose coupling, where distributed models run in sequence, and one model uses the known output values, based on the values at the previous time steps, of the coupled model. The feedback between the programs is lagged one coupling time step.

• Fully-dynamic coupling, also called strong or tight coupling, where distributed models iterate within each time step until the error estimate falls within a predefined tolerance.