Which one of the following statements regarding TCP$/$IP is FALSE?

a$.$

CP$/$IP is a set of protocols organised in different layers.

b$.$

In a simple network some of the TCP$/$IP layers may be omitted.

c$.$

TCP$/$IP is a hierarchical protocol made up of interactive modules, each with its own functionality.

d$.$

In TCP$/$IP each upper level protocol is supported by the services of one or more lower level protocols.