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The 7 Layer OSI Model
(Originally posted in Feb 2003 supporting an article on VPNs and Wi-Fi. See more about startups and product strategy at http://www.mironov.com/articles/topical).
Network and protocol developers need to keep their words organized. The OSI model helps sort out some of the communications issues that crop up in the real world. In particular, the model helps to match “like” items on each side of a machine-to-machine communication.
Back in the dark ages of the 1970’s and 80’s, we saw various networking “wars” as competitors tried to define the next layer of standards to their advantage and get partners/customers to support them. Coaxial cable was pushed aside by 10Base-T; Ethernet wrestled with ArcNet and Token Ring; AppleTalk bigots made fun of the short trousers that TCP/IP folks wore. IBM’s SNA architecture, which pre-dated a clean OSI model, continues to confuse all who came after it.
A typical OSI Layer diagram might show
My February 2003 article focused on Layer 2 (the Data Link or Link Layer) and Layer 3 (the Network Layer). Without a reference model of this kind, most technical networking discussions would be impossible. Two typically good expositions on the full model and its layers are from Cisco and from RAD Data Communications, although hundreds more exist.
The huge economic win of an industry that supports this kind of rational model is in the ability of companies to innovate at a particular level. WiFi is one possible replacement for Ethernet at Layer 2. If implemented correctly, networks can include many different segments with alternate Layer 2 technologies: a little WiFi here, a little HPNA home network via power lines there. Applications living at higher levels function in blissful ignorance of the underlying layers. Corporations shifting from 10Base-T to 100Base-T to 1000Base-T need some switches and conversion boxes, but don’t have to tell most of their users that changes are being made.