I can change a link layer protocol and the application layer

I can change a link layer protocol and the application layer protocol does not need to know or be made aware of the change. Explain why?

Solution

sol:
yes its need not to be know if there is any change because
the internet uses one of the standard method for communication that is nothing but tcp/ip ,generally higher layers
does not identify the lower layer.when we see the lower layer from higher layer there are abstracted,so they dont know what is internally happening in the lower layers