Same-layer interaction on different computers<p>
The two computers use a protocol to communicate with the same layer on another computer. The protocol defined by each layer uses the header that is transmitted between the computers, to communicate what each computer wants to do.<p>
Adjacent-layer interaction on the same computer<p>
On a single computer, one layer provides a service to a higher layer. The software or hardware that implements the higher layer request that the next lower layer perform the needed function.