Hi Shahid
You have no need to use Dynamic switch as you are using only one Tx.
For buffer working read this
Because the majority of OptiSystem components will not calculate if a signal is not available at the input ports, the Iterations and Initial delay parameter will help the user to avoid a situation in which the simulation will not perform because a component cannot find signals at the input port – and the system will be deadlocked.
The concept of multiple iterations and delays is very confusing, because it does not have a physical meaning. It is a simulation technique and requires an understanding of the calculation scheduler of OptiSystem.
If you need to know more go through this optiwave tutorial
Lesson 5: Bidirectional Simulation — Working with Multiple Iterations