$($a$)$ The Open System Interconnect $($OSI$)$ model is a conceptual framework that organizes

the functionality of any type of communication in a layered structure.

$($i$)$ Give the Protocol Data Units that are used at layers $2,3$ and $4$ of the OSI model.

$($ii$)$ Which network device functions only at Layer $1$ of the OSI model?

$($iii$)$ Draw a diagram that shows $($in the correct order$),$ the layers of the TCP$/$IP

protocol stack that are implemented on the following network components:

A$.$ End System $($host$)$;

B$.$ Router;

C$.$ Switch.