The history of Ethernet is fascinating. The reason why we have three different frame types is that DIX used the Ethernet II frame that is prevalent today, while IEEE intended to use a different frame format that could be used for different MAC layers, such as token bus, token ring, FDDI, and so on. The IEEE were also inspired by HDLC, and modeled their frame header more in alignment with the OSI reference model that had the concept of SAPs. When they discovered that the number of available SAPs weren’t enough, they made an addition to the 802 standard to support SNAP frames. In networks today, Ethernet II is dominant, but some control protocols may use LLC and/or SNAP frames.
↫ Daniel Dib
I just smiled and nodded.