<P> ICMP & IGMP operate on top of IP but do not transport data like UDP or TCP . Again, this functionality exists as layer management extensions to the OSI model, in its Management Framework (OSIRM MF) </P> <P> The SSL / TLS library operates above the transport layer (uses TCP) but below application protocols . Again, there was no intention, on the part of the designers of these protocols, to comply with OSI architecture . </P> <P> The link is treated as a black box . The IETF explicitly does not intend to discuss transmission systems, which is a less academic but practical alternative to the OSI model . </P> <P> The following is a description of each layer in the TCP / IP networking model starting from the lowest level . </P>

It is a layer under the internet protocol suite that defines how router will connect with each other