If you look at Figure 1, you will see a very complex diagram of the various flavors of Ethernet using the definitions of 802.3. Notice that the possible data rates can range from 1 Mbps to 1000 Mbps. The 10000 Mbps rate is yet to be added to the standard and 1 Mbps is not popular. We will concentrate on the 10 Mbps and 100 Mbps options. In terms of the OSI Reference Model, all the data rate variations are considered physical layer attributes, while the data link layer is common to all data rate variations. The 802.3 model does not even address the upper layers of the OSI model.

Figure 1 — The complete 802.3 model only addresses two layers of the OSI Reference Model.

Of course, the 10 Mbps versions are the simplest. However, notice that two are shown in the figure. The one on the left is the traditional model showing the Attachment Unit Interface (AUI). At this point any physical medium can be attached by way of the DB-15 AUI connector. This was the connector originally used to attach to a 10BASE5 (thick trunk) transceiver which was usually mounted in the ceiling. In 802.3 terms, this transceiver would be called a Physical Medium Attachment (PMA) or simply a Medium Attachment Unit (MAU). In order to get down to the Physical Layer Signaling (PLS) of the Ethernet interface, an AUI cable, or drop cable, is used acting like an extension cord. On one end is a male DB-15 and the other is a female DB-15. The AUI port is medium independent. If a fiber optic medium is desired, the appropriate MAU would be connected to the AUI port. On the fiber optic side, the fiber optic cables would be connected to the Medium Dependent Interface (MDI), which would include ST-style fiber optic connectors. This completes the connection to the medium.

With the introduction of Fast Ethernet, the model changed somewhat. A new connection was defined called the Media Independent Interface (MII). It provided more bandwidth at 100 Mbps than could be provided by the AUI interface. Notice that at 10 Mbps, the MII is inserted between the PLS and the Reconciliation interface. This is shown to the immediate right of the traditional model. Further to the right is the 100 Mbps variation which introduces additional terms. The Physical Medium Dependent now attaches to the MDI and the Physical Coding Sublayer (PCS) attaches to the MII. In the middle is the PMA. Collectively, the PCS, PMA and PMD are termed the PHY for Physical Layer Device. The MII connector is defined as 50 mm wide dual row, 40 pin. Like the AUI, it is only an option. Most Ethernet interfaces only provide the necessary MDI connector and nothing else. To understand the standard these terms and connections must be defined. You might have asked why a MII interface was defined for 10 Mbps Ethernet when an AUI seems to have served the industry quite well? The MII interface supports both 10 Mbps and 100 Mbps data rates which is key to providing dual speed support between legacy 10 Mbps and newer 100 Mbps systems. On the other hand, the AUI only supports 1 Mbps and 10 Mbps while the new Gigabit Medium Independent Interface (GMII) only supports 1000 Mbps.

100BASE-T

Management Interface