One of the most enduring models in networking is the famous seven-layer OSI model. X.25 roughly, but pretty accurately, is based on the first three layers. And it stopped there. Subsequently ...

The Internet Protocol layer is comparable to layer 3 in the OSI model. The host-to-host layer is equivalent to OSI layer 4. These are the TCP and UDP (user datagram protocol) functions.

When troubleshooting network issues it’s helpful to understand if the issue is occurring at Layer 2 or Layer 3 of the OSI model.

This is a good example of de-cerebralisation in action. The 4-7 layer band in the OSI 7-layer network model covers some important tasks, such as load-balancing.