Add a {@link TransportLayer} to the transport, wrapping the input and output process handlers
in the state they currently exist. No effect if the given layer was previously added.
@param layer the layer to add (if it was not previously added)
@throws IllegalStateException if processing has already started.
Add a {@link TransportLayer} to the transport, wrapping the input and output process handlers in the state they currently exist. No effect if the given layer was previously added.
@param layer the layer to add (if it was not previously added) @throws IllegalStateException if processing has already started.