A network is any two or more entities -- be they people, organizations, machines, or whatever -- that:
Before a network can be effective, participants must have clearly established these three things.
In computer networking, fortunately, the services, transmission media, and protocols have long since been codified so that the uninitiated can quickly master the concepts.
Since 1977, the International Standards Organization (ISO) has promulgated the Open Systems Interconnection (OSI) Reference Model. The OSI seven-layer model, as it has come to be known, consists of (get this!) seven layers:
The seven layers collectively are often referred to as a protocol stack, although in actuality only the transport and higher layers deal directly with protocols, per se.
Each layer is responsible for specific functions of network communications. It is important to note, however, that the model is theoretical; actual network operating systems (NOSs) handle the practical implementation of each of these theoretical functions in different ways. Nevertheless, the model does help clarify the relationships and define the interactions the multiple protocol stacks of the various NOSs have to and with one another.
In networking, each layer in a computer's protocol stack communicates with the corresponding layers in other computers' stacks. This works both horizontally and vertically:
Let's get into the meat of the layers, starting at the bottom with layer 1, the Physical Layer.
Nah, I want to skip ahead:
Copyright 1999, Marc Elliot Hall, DBA Sensation! Services