Ethernet

IEEE 802.3 is a standard for Ethernet networking technology in the data link layer of the OSI model. It defines the physical layer and the media access control (MAC) sublayer for Ethernet networks, including wired networks using twisted pair, fiber optic, and coaxial cables, as well as wireless networks.

The standard specifies various parameters, including the maximum cable length, minimum frame size, and maximum transmission rate. The maximum cable length for a standard Ethernet network is 100 meters for twisted pair and 2 kilometers for fiber optic.

There are three types of Ethernet:

1. 10Base-T Ethernet: It is the most commonly used Ethernet standard, also known as twisted pair Ethernet. It uses a twisted pair cable to transmit data at 10 Mbps and supports a maximum cable length of 100 meters.
2. 100Base-T Ethernet: It is also known as Fast Ethernet, and it uses a twisted pair cable to transmit data at 100 Mbps. It supports a maximum cable length of 100 meters.
3. 1000Base-T Ethernet: It is also known as Gigabit Ethernet, and it uses a twisted pair cable to transmit data at 1 Gbps. It supports a maximum cable length of 100 meters.

The standard also includes provisions for full-duplex communication, which allows devices to transmit and receive data simultaneously, as well as for error detection and correction through the use of cyclic redundancy check (CRC) codes.

The frame format of Ethernet includes the following fields:

1. Preamble: It is a 7-byte field consisting of alternating 0s and 1s, which is used to synchronize the receiver clock.
2. Start Frame Delimiter (SFD): It is a 1-byte field indicating the start of the Ethernet frame.
3. Destination MAC Address: It is a 6-byte field indicating the MAC address of the intended recipient.
4. Source MAC Address: It is a 6-byte field indicating the MAC address of the sender.
5. Length/Type: It is a 2-byte field indicating the length or type of the data field that follows. If the value is less than or equal to 1500, it indicates the length of the data field. If the value is greater than 1500, it indicates the type of the protocol used in the data field.
6. Data: It is a variable-length field that contains the actual data being transmitted.
7. Frame Check Sequence (FCS): It is a 4-byte field used for error detection, and it contains a cyclic redundancy check (CRC) value calculated over the entire Ethernet frame.

The frame format of Ethernet may vary slightly for different types of Ethernet, such as 10Base-T, 100Base-T, and 1000Base-T. However, the basic structure remains the same. IEEE 802.3 has been revised and updated several times since its initial publication, with the most recent version being IEEE 802.3cg, which was released in 2019 and specifies Ethernet networks over single-pair copper cabling.