3.2 Layer 2 Protocol Overview - LAN Protocols
3.2.2 Ethernet vs. IEEE 802.3
Ethernet and IEEE 802.3 specify similar technologies. Both are implemented in carrier sense multiple access collision detect (CSMA/CD) LANs. Stations on a CSMA/CD LAN can access the network at any time. Before sending data, CSMA/CD stations "listen" to the network to see if it is already in use. If it is, the station wishing to transmit waits for the wire to be 'clear'. If the network is not in use, the station transmits. A collision occurs when two stations listen for network traffic, 'hear' none, and transmit simultaneously. In this case, both transmissions are damaged, and the stations must retransmit at some later time. Backoff algorithms determine when the colliding stations retransmit. CSMA/CD stations can detect collisions, so they know when they must retransmit.

Both Ethernet and IEEE 802.3 LANs are broadcast networks. In other words, all stations see all frames, regardless of whether they are an intended destination. Each station must examine received frames to determine whether the station is the desired destination. If it is the destination, the frame is passed to a higher protocol layer for appropriate processing.

Differences between Ethernet and IEEE 802.3 LANs are subtle. Ethernet provides services corresponding to Layers 1 and 2 of the OSI reference model, whereas IEEE 802.3 specifies the physical layer (Layer 1) and the media-access portion of the link layer (Layer 2), but does not define a logical link control protocol. Both Ethernet and IEEE 802.3 are implemented in hardware. Typically, the physical manifestation of these protocols is either an interface card in a host computer or circuitry on a circuit board within a host computer.

IEEE 802.3 specifies several different physical layers, whereas Ethernet defines only one. Each IEEE 802.3 physical-layer protocol has a name that summarizes its characteristics. The coded components of an IEEE 802.3 physical-layer name are shown in Figure . The characteristics of each IEEE 802.3 media type are listed in Figure .

Ethernet is most similar to IEEE 802.3 10BASE5. Both of these protocols specify a bus topology network with a connecting cable between the end stations and the actual network medium. In the case of Ethernet, that cable is called a transceiver cable. The transceiver cable connects to a transceiver device attached to the physical network medium. The IEEE 802.3 configuration is much the same, except that the connecting cable is referred to as an attachment unit interface (AUI), and the transceiver is called a media attachment unit (MAU). In both cases, the connecting cable attaches to an interface board (or interface circuitry) within the end station.