un/forced state

opnet process 域建模时涉及到的两个状态：

文档解释如下：

An unforced (red) state is one that returns control of the simulation to the Simulation Kernel after executing its enter executives.  执行完enter 部分的代码后会 block。。

A forced (green) state is one that does not return control, but instead immediately executes the exit executives and transitions to another state.  执行完enter部分的代码，会执行exit部分的代码，然后转入下一个state

其实这个和交通灯是一个道理啦~~~