What is Ethernet?

Ethernet is a wired networking technology used to connect devices within a Local Area Network (LAN). It allows devices to communicate and exchange data through cables and is standardized under IEEE 802.3.

Ethernet operates at two layers of the OSI model:

• Physical Layer (Layer 1): Defines the cables, connectors, signals, and transmission speeds used to transmit data.
• Data Link Layer (Layer 2): Handles Ethernet frames, MAC addressing, and error detection during communication.

Evolution of Ethernet

Ethernet was invented by Robert Metcalfe in 1973, initially supporting a data rate of approximately 2.94 Mbps.

• 1982: Ethernet Version 2 was introduced with a 10 Mbps data rate.
• 1983: IEEE standardized Ethernet under the IEEE 802.3 standard.
• Later developments: Ethernet evolved to support 100 Mbps, 1 Gbps, 10 Gbps, 40 Gbps, 100 Gbps, and higher data rates.

Types of Ethernet

Ethernet has evolved into different types based on data transmission speed, cable type, and network architecture.

1. Fast Ethernet

Fast Ethernet is an Ethernet technology that supports a data transmission speed of 100 Mbps. It is an improved version of traditional Ethernet, which operates at 10 Mbps.

• Speed: 100 Mbps.
• Media: CAT5 twisted-pair (CAT3 for 100BASE-T4) and fiber-optic cables.
• Variants: 100BASE-TX, 100BASE-FX, and 100BASE-T4.

2. Gigabit Ethernet

Fast Ethernet is an Ethernet technology that supports a data transmission speed of 100 Mbps. It is an improved version of traditional Ethernet, which operates at 10 Mbps.

• Speed: 100 Mbps.
• Media: CAT5 twisted-pair and fiber-optic cables.
• Variants: 100BASE-TX, 100BASE-FX, and 100BASE-T4.

3. 10-Gigabit Ethernet

10-Gigabit Ethernet is an advanced Ethernet technology that supports data transmission speeds of 10 Gbps. It is mainly used in data centers, enterprise networks, and high-performance computing environments where large amounts of data need to be transferred quickly.

• Speed: 10 Gbps.
• Media: CAT6a, CAT7, and fiber-optic cables.
• Supports long-distance communication using fiber-optic cables.

4. Switched Ethernet

Switched Ethernet is a network architecture that uses switches to connect multiple devices within a LAN. Each device gets a dedicated connection to the switch, allowing simultaneous data transmission.

• Each switch port creates a separate collision domain.
• Supports different Ethernet speeds, such as 10 Mbps, 100 Mbps, 1 Gbps, and 10 Gbps.

How Ethernet Works

Ethernet works by transmitting data between connected devices in the form of frames. The communication process involves the following steps:

• Data Encapsulation: When a device sends data, Ethernet adds a header and trailer to the data to create an Ethernet frame. The header contains the source and destination MAC addresses, while the trailer contains the Frame Check Sequence (FCS).
• Frame Transmission: The Ethernet frame is converted into electrical or optical signals and transmitted through the network cable.
• Frame Reception: The receiving device checks the destination MAC address to determine whether the frame is intended for it. If the address matches, the frame is accepted for further processing.
• Error Checking and Data Delivery: The receiving device uses the FCS field to detect transmission errors. If an error is detected, the frame is discarded. Otherwise, the frame is processed, and its data is delivered to the appropriate network layer.

Ethernet Frame Format

An Ethernet frame is the basic unit of data transmission at the Data Link Layer. It contains several fields that help identify the sender, receiver, and data being transmitted.

Note: The Preamble (7 bytes) and Start Frame Delimiter (SFD) (1 byte) are transmitted before the Ethernet frame and are not considered part of the Ethernet MAC frame.

Ethernet Access Mechanism

CSMA/CD (Carrier Sense Multiple Access with Collision Detection)

CSMA/CD is a media access control mechanism used in traditional shared and half-duplex Ethernet networks to manage data transmission and detect collisions.

It works through the following steps:

1. Carrier Sense: A device first checks whether the network medium is free before transmitting data.
2. Transmission: If the medium is idle, the device starts transmitting data. If it is busy, the device waits until it becomes available.
3. Collision Detection: If two devices transmit data simultaneously, a collision occurs, which is detected by the devices.
4. Jam Signal: The devices send a jam signal to notify other devices about the collision and stop transmission.
5. Backoff: Each device waits for a randomly selected period using the Binary Exponential Backoff algorithm before attempting to retransmit the data.
6. Abort: If 16 transmission attempts fail, the device aborts the transmission and reports an error.

Note: CSMA/CD is not used in modern full-duplex switched Ethernet networks because devices have dedicated communication links and collisions do not occur during normal operation.

Encoding Technique

Ethernet uses different encoding techniques depending on the Ethernet standard and transmission speed.

Manchester Encoding is used in traditional 10 Mbps Ethernet. It represents each bit through a transition in the middle of the bit period.

• Bit 0: High-to-low transition.
• Bit 1: Low-to-high transition.

Note: Manchester encoding is associated with traditional 10 Mbps Ethernet and is not used by every modern Ethernet standard.

Key Features of Ethernet

• Reliability: Uses error detection mechanisms to identify transmission errors.
• Cost-Effectiveness: Uses widely available networking cables and hardware.
• Interoperability: IEEE 802.3 standards ensure compatibility between Ethernet devices.
• Scalability: Allows additional devices to be connected through network switches.
• Compatibility: Supports higher-layer protocols such as IP, which carries transport-layer protocols such as TCP.