Ethernet (802.3)

Ethernet is the most common local area network (LAN) technology for data transmission between computers and other network devices. Defined under the IEEE 802.3 standard, Ethernet operates at the physical and data link layers of the OSI model. This technology transmits data in frames and belongs to a broad family of standards supporting various speeds and media types.

History and Development

Ethernet was developed in 1973 at Xerox PARC by Robert Metcalfe and his team. The first version operated at 2.94 Mbps and used thick coaxial cables for transmission. In 1980, the first commercial Ethernet standard, operating at 10 Mbps, was introduced by the Digital Equipment Corporation, Intel, and Xerox (DIX) consortium. In 1983, IEEE published this standard officially as IEEE 802.3.

Working Structure

Ethernet performs data transmission based on MAC (Media Access Control) addresses. Each device has a unique 48-bit MAC address. Ethernet operates at the second layer of the OSI model and handles functions such as framing, addressing, and error control.

Ethernet frames consist primarily of the following fields:

• Preamble
• Destination MAC address
• Source MAC address
• Type/Length field
• Data payload
• Frame Check Sequence (FCS)

During transmission, the CSMA/CD (Carrier Sense Multiple Access with Collision Detection) access method is used to monitor the state of the network medium. This method detects collisions that may occur when two devices transmit data simultaneously and reschedules transmission accordingly.

Ethernet Types

Ethernet technology has been classified over time according to different speeds and media:

Modern Ethernet standards have been developed to operate over both copper and fiber optic cables.

IEEE 802.3 Standard

The Ethernet protocol was officially standardized by IEEE in 1983 as the IEEE 802.3 standard. This standard defines electrical/optical signaling at the physical layer and frame structure and access control methods at the data link layer.

The IEEE 802.3 standard has been updated over time with numerous extensions published as sub-standards supporting different speeds and media. For example:

• 802.3u → Fast Ethernet (100 Mbps)
• 802.3ab → Gigabit Ethernet (1 Gbps)
• 802.3an → 10 Gigabit Ethernet
• 802.3ae → 10 GbE over fiber
• 802.3bz → 2.5G/5G Ethernet

All these standards preserve the fundamental structure and communication logic of Ethernet frames, differing only in speed and physical medium.

Ethernet Frame

In Ethernet technology, data transmission is carried out through data blocks called frames, which have a specific structure. These frames contain both the data to be transmitted and the control information necessary to ensure the data reaches its destination reliably and without error.

An Ethernet frame typically consists of seven main components. First, a 7-byte field called the Preamble precedes transmission. The regular bit pattern in this field (for example, 10101010...) helps the receiving device synchronize its timing with the sender. Immediately following is the Start Frame Delimiter (SFD), a 1-byte special marker indicating the start of the frame.

The next section of the frame contains the destination MAC address, identifying the device to which the data is being sent, followed by the source MAC address of the transmitting device. These addresses are each 6 bytes long and physically identify network devices.

After the addresses comes a 2-byte Type/Length field. According to the IEEE 802.3 standard, this field specifies the length of the data payload. In contrast, in DIX (Ethernet II) frames, this field identifies the protocol carried in the upper layer (such as IPv4 or ARP).

The largest part of the frame is the data and padding field, which carries the data from the upper layer. The minimum data length is 46 bytes and the maximum is 1500 bytes. If the transmitted data is shorter than 46 bytes, additional padding is added to meet the minimum frame size requirement.

Finally, the Frame Check Sequence (FCS) field ensures frame integrity. This 4-byte section contains a CRC (Cyclic Redundancy Check) code generated by the sender. The receiver applies the same CRC algorithm to verify whether any errors occurred during transmission.

This structure enables Ethernet to provide both reliable and high-speed data transmission. Additionally, the fixed frame structure ensures the protocol operates consistently across different speeds and media types.

Applications

Due to its flexibility and low cost, Ethernet is widely used both in home networks of individual users and in corporate data centers. Its most common applications include:

• Local area networks (LAN)
• Campus networks
• Data centers
• Industrial automation systems
• Connections between network devices (switches, routers, access points, etc.)

Fiber Optic Cables and Ethernet

With the growing demand for high-speed data transmission, the Ethernet protocol has also been adapted for use over fiber optic media. Protocols defined under the IEEE 802.3 standard such as 100BASE-FX, 1000BASE-SX/LX, and 10GBASE-SR/LR operate over fiber cables. These protocols preserve the Ethernet frame structure, enabling longer-distance connections with lower latency. Fiber infrastructure is preferred in environments requiring high bandwidth, such as data centers and backbone networks.