Welcome

• 1: Introduction to Ethernet
• 1.1: The OSI Model
• 1.2: The Ethernet Standards
• 1.3: The Ethernet System
• 2: Miscellaneous
• 3:

1 - Introduction to Ethernet

Ethernet plays a crucial role in local area networks (LANs) , by connecting wired networked devices within a limited geographical area.

As you may notice, Ethernet itself does not directly participate in internet connections. Instead, it is a local network technology primarily used to facilitate efficient and secure data exchange between devices like computers and printers, serving as the foundation for larger networks, including data centers and internet infrastructure.

To better understand Ethernet and its functionalities, let’s explore it through the lens of the Open Systems Interconnection (OSI) model first. Then, Ethernet standards will be presented, followed by an introduction to the Ethernet system including its basic elements and protocols.

1.1 - The OSI Model

Layers of the OSI Model

The Open Systems Interconnection (OSI) reference model is a conceptual framework that divides network operations into seven layers:

• Application Layer:

  • Provides ​network services directly to end-user applications, how?
    • User interface
    • Specific rules (protocols) for different apps
    • Data semantics

• Presentation Layer:

  • Ensures data sent by one application can be correctly interpreted by another¹, and also ensures secure², and efficient communication³:
    1. Data format conversion
    2. Data encryption/decryption
    3. Data compression

• Session Layer:

  • Manages and controls connections (ie, sessions) between applications

• Transport Layer:

  • Provides end-to-end error recovery mechanisms
    • TCP (Transmission Control Protocol) for accurate communication
    • UDP (User Datagram Protocol) for fast communication

• Network Layer:

  • Establishes communications across different networks
    • Logical addressing: assigns unique IP addresses to devices
    • Routing: finds the best path for data to travel between source and destination

• Data Link Layer:

  • Ensures ​reliable data transfer between devices within the same network (LAN)
  • Has two sublayers:
    • Logical Link Control (LLC)
    • Media Access Control (MAC)

• Physical Layer:

  • Defines how data is transmitted as:
    • Electrical signals over copper cables
    • Optical signals over fiber
    • Radio signals over radio waves

Among the seven layers, Ethernet covers Media Access Control (MAC) from Data Link Layer (Layer 2) and Physical Layer (Layer 1). To better understand the networking functions of each layer and the role of Ethernet in the process, see the next section for an example.

Example Scenario

Here is a step-by-step breakdown of the process of an example scenario, where a user types www.example.com in a web browser and presses “Enter”, attempting to fetch the webpage from the remote server:

1. Application Layer (Layer 7)

   The user browser generates an ​HTTP/HTTPS GET request for www.example.com, during which a DNS (Domain Name System) server is used to resolve www.example.com to an IP address, such as an IPv4 address of 192.168.1.1.

2. Presentation Layer (Layer 6)

   Before transmission, encrypt the request with TLS (Transport Layer Security) if the sites uses HTTPS, and the data is compressed.

3. Session Layer (Layer 5)

   A session is established between the user browser and the server, to handle authentication (such as login credentials, if applicable), maintain the communication flow, and manage persistent connections for subsequent interactions.

4. Transport Layer (Layer 4)

   TCP (Transmission Control Protocol) is used in this case for connection-oriented, reliable delivery. Data is broken into ​segments (TCP Header + payload) for transmission.

5. Network Layer (Layer 3)

   The segments are further packed into IP packets (IP Header + payload). Routing is based on IP addresses, which are obtained by querying a DNS (Domain Name System) server.

6. Data Link Layer (Layer 2)

   The IP packet is wrapped inside an Ethernet frame (MAC Header + payload + Trailer), which adds the source and destination MAC addresses, to be transmitted between devices on the ​same local network. The Ethernet frame is sent from the user computer to the router.

   Note

   If the user is using WI-FI instead of wired Ethernet, the IP packet is wrapped inside Wi-Fi frames, which will then be converted into ​radio signals in the Physical Layer.

7. Physical Layer (Layer 1)

   Ethernet frames are converted into ​bits (0s and 1s) and transmitted via ​electrical signals (over copper) or ​light pulses (fiber).

8. On the server side:

   → Converts the bitstream into structured ​Ethernet frames.

   → Checks the ​destination MAC address and validates the frame’s integrity.

   → Strips the Ethernet header/trailer and reads the IP packet.

   → Verifies the IP address and passes the TCP segment to the Transport Layer.

   → Checks for errors and passes the reassembled data stream to the Application Layer.

   → Processes the HTTP request and fetches the requested resource (in this case, it is the web page).

   → Sends back an HTTP response, which is broken into TCP segments → ​Encapsulated into IP packets → ​Wrapped in new Ethernet frames → ​Transmitted as bits back to the client.

The Role of Ethernet

From the above example, we can identify the role of Ethernet in the following aspects:

• Local Communication: Ethernet handles data transfer between devices on the same network (in this example, the user’s computer and the router).
• MAC Addressing: Ethernet uses MAC addresses to uniquely identify devices on a ​local network, ensuring frames reach the correct device on the LAN.
• ​Error Detection: The Frame Check Sequence (FCS) in Ethernet frames verifies data integrity.

1.2 - The Ethernet Standards

Overview of Ethernet Standards

IEEE, short for Institute for Electrical and Electronics Engineers, is an institute that develops standards in many industries, and the Ethernet standards are developed by IEEE-SA, IEEE Standards Association. Today, IEEE 802.3 serves as the standard that defines Ethernet protocols, providing the foundation for modern wired network communications.

The goal of this standardization is to ensure equipments are compatible (inter-operation), so as to expand marketplace and benefit both manufacturers and consumers. Therefore, devices not specified within the IEEE 802.3 standard are typically vendor-specific.

IEEE Supplements

A letter designation is used to address different types of media and technologies used in Ethernet networks. For example:

Note that standards developing and publishing lags behind the innovation, especially in the field of computer networking. Therefore, it’s possible, and not necessarily a drawback, for a product to be built to draft standards.

IEEE Media System Identifiers

There are three key components of identifiers:

• Speed: indicates the data transmission rate, such as 10 Mbps, 100 Mbps, or 1 Gbps
• Type of signaling: indicates the transmission method, such as baseband signaling or encoding schemes
• Physical medium: indicates the type of cable, such as twisted-pair, fiber optic, or coaxial cable

The following table provides a detailed breakdown of these identifiers and their meanings:

1.3 - The Ethernet System

Half-Duplex and Full-Duplex Modes

Previously, before the emergence of Ethernet switches, half-duplex mode is the typical operation for Ethernet devices.

In half-duplex mode:

• Multiple computers communicate over a single Ethernet channel via the CSMA/CD MAC protocol .
• A station (ie., the networked device) first listens to the channel, and if the channel is idle, the station transmits its data (Ethernet frames).
• Only one station can send data over the Ethernet channel at any given time.
• Data transmission rate: 10 Mb/s or 100 Mb/s

Nowadays, full-duplex mode is widely adopted by Ethernet devices and is typically enabled through the Auto-Negotiation protocol.

In full-duplex mode:

• Each station connected to a switch port does not share the Ethernet channel bandwidth on that link with any other computer.
• Devices can send and receive data simultaneously.

The Four Basic Elements of Ethernet

• The Ethernet frame — A standardized set of bits

• The Media Access Control protocol (MAC) — A set of rules embedded in each Ethernet interface that allow Ethernet stations to access the Ethernet channel, in either half-duplex or full-duplex mode

• The signaling components — Standardized electronic devices that send and receive signals over an Ethernet channel

• The physical medium — The cables and other hardware used to carry the digital Ethernet signals between computers attached to the network

2 - Miscellaneous

Coming soon!

3 -