Since the creation of Ethernet in 1973, standards have evolved for specifying faster and more flexible versions of the technology. This ability for Ethernet to improve over time is one of the main reasons that it has become so popular. Early versions of Ethernet were relatively slow at 10 Mbps. The latest versions of Ethernet operate at 10 Gigabits per second and faster. Figure 1 highlights changes in the various versions of Ethernet.
At the data link layer, the frame structure is nearly identical for all speeds of Ethernet. The Ethernet frame structure adds headers and trailers around the Layer 3 PDU to encapsulate the message being sent.
Both the Ethernet header and trailer have several sections of information that are used by the Ethernet protocol. Each section of the frame is called a field. As shown in Figure 2, there are two styles of Ethernet framing:
- IEEE 802.3 Ethernet standard which has been updated several times to include new technologies
- The DIX Ethernet standard which is now referred to Ethernet II
The differences between framing styles are minimal. The most significant difference between the two standards is the addition of a Start Frame Delimiter (SFD) and the change of the Type field to a Length field in the 802.3.
Ethernet II is the Ethernet frame format used in TCP/IP networks.