|  | 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 1s and 0s 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.