|  | 7.3 | Ethernet and IEEE 802.3
| 7.3.3 | Ethernet frame format

The Ethernet and IEEE 802.3 frame fields are described in the following summaries:

- preamble - The alternating pattern of 1's and 0's tells receiving stations that a frame is Ethernet or IEEE 802.3. The Ethernet frame includes an additional byte that is the equivalent of the Start of Frame (SOF) field specified in the IEEE 802.3 frame.

- start-of-frame (SOF) - The IEEE 802.3 delimiter byte ends with two consecutive 1 bits, which serve to synchronize the frame-reception portions of all stations on the LAN. SOF is explicitly specified in Ethernet.

- destination and source addresses - The first 3 bytes of the addresses are specified by the IEEE on a vendor-dependent basis. The last 3 bytes are specified by the Ethernet or IEEE 802.3 vendor. The source address is always a unicast (single-node) address. The destination address can be unicast, multicast (group), or broadcast (all nodes).

- type (Ethernet) - The type specifies the upper-layer protocol to receive the data after Ethernet processing is completed.

- length (IEEE 802.3) - The length indicates the number of bytes of data that follows this field.

- data (Ethernet) - After physical-layer and link-layer processing is complete, the data contained in the frame is sent to an upper-layer protocol, which is identified in the type field. Although Ethernet version 2 does not specify any padding, in contrast to IEEE 802.3, Ethernet expects at least 46 bytes of data.

- data (IEEE 802.3) - After physical-layer and link-layer processing is complete, the data is sent to an upper-layer protocol, which must be defined within the data portion of the frame. If data in the frame is insufficient to fill the frame to its minimum 64-byte size, padding bytes are inserted to ensure at least a 64-byte frame.

- frame check sequence (FCS) - This sequence contains a 4 byte CRC value that is created by the sending device and is recalculated by the receiving device to check for damaged frames.