The OSI model was created by telecom people, not computer people. This is important because the two groups have radically different views of what networks are f

The OSI model was created by telecom people, not computer people. This is important because the two groups have radically different views of what networks are for and how they work, to the extent that they spent a lot of the 80s and 90s talking past each other. In the telecom world at that time the fundamental unit was the "circuit", meaning a two-way voice telephone call. The upper frequency limit of a voice circuit is 4kHz, so the Nyquist criterion said that digitising a voice circuit required 8,000 samples per second. The required signal to noise ratio fit nicely into 8 bits, so a digital circuit was 64,000 bits per second each way, with strong real-time jitter and latency guarantees (because, voice). If you weren't using the link for a while you still had to pay for it by the second because you were getting the guaranteed 64,000 bits per second all the time; that bandwidth was reserved for your use and nobody else could mop up the spare. Meanwhile the correctness of the received data was best-effort because the odd corrupt bit isn't an issue in a voice circuit. If you wanted more bandwidth then you could pay for multiple circuits to the same destination. In telecoms all the intelligence goes into the exchanges; the phone is merely a dumb end-point. If you want services like call forwarding you type numbers into the phone, but all the application software lives at the exchange. If you talked to telecom engineers about the future, they would talk about video calls. They would be just like phone calls but with higher bandwidth. Meanwhile the computer people needed the exact opposite to what a voice circuit provides. If you send a file another computer you need it to arrive bit-for-bit accurate, but you don't much care about bandwidth and latency. While a physical pipe has a certain capacity, you don't need or want to reserve bandwidth on it, you just want the data to move as fast as physically possible. So telecom people wanted to provide a smart network connecting dumb end-points, with guaranteed bandwidth and latency with best-effort correctness, while computer people wanted to connect smart end-points to a dumb network that provided guaranteed correctness but only best-effort bandwidth and latency. Things got worse when the Web started being used by people at home. Now most of the data was flowing in one direction, but circuits were fundamentally about equal bi-directional communication. So now half of that expensive bandwidth was being wasted. The "adults in the room" attitude of the telcos didn't help; they had over a century of experience running international telecom networks and thought they knew how to do it. Therefore they weren't interested in the opinions of those hairy computer guys. For more on this, read "Mother Earth, Mother Board" by Neal Stephenson.