Cuncti adsint meritaeque expectent praemia palmae — “May all be here, and may those who have earned the palm await their rewards.” (Aeneid 5.64, Virgil)
Welcome to my knowledge base!
This site is a collection of my study and reading notes on Ethernet and networking concepts, written from the perspective of a technical writer in the semiconductor industry.
Topics cover Ethernet standards and protocols, Ethernet frame structure, and Ethernet switches in network communication. If you are new to this area, I hope you find these notes helpful!
The content is a work in progress — I’m still organizing my previous notes, and new content will grow over time.
While this site is primarily designed to introduce Ethernet, future additions may also include PCIe (computer communication and interconnect technologies), as well as Python scripting and web development out of personal interest.
If you have any questions or spot any inaccuracies, feel free to contact me!
1 - Introduction to Ethernet
What is Ethernet’s role in the OSI model? What are Ethernet standards? What are basics about an Ethernet system?
“Man is something that shall be overcome. What have you done to overcome him?” (Thus Spoke Zarathustra, Nietzsche)
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
“Man is something that shall be overcome. What have you done to overcome him?” (Thus Spoke Zarathustra, Nietzsche)
Layers of the OSI Model
The Open Systems Interconnection (OSI) reference model is a conceptual framework that divides network operations into seven layers:
OSI Model
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:
Data format conversion
Data encryption/decryption
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.
Note
The OSI model is only a framework, not an architecture or blueprint for network design. However, the OSI model provides a common organizational scheme for network standardization.
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:
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.
Presentation Layer (Layer 6)
Before transmission, encrypt the request with TLS (Transport Layer Security)
if the sites uses HTTPS, and the data is compressed.
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.
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.
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.
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.
Physical Layer (Layer 1)
Ethernet frames are converted into bits (0s and 1s) and transmitted via electrical signals (over copper) or light pulses (fiber).
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
“Man is something that shall be overcome. What have you done to overcome him?” (Thus Spoke Zarathustra, Nietzsche)
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:
Supplement
Description
802.3u-1995
100BASE-T Fast Ethernet and Auto-Negotiation
802.3z-1998
1000BASE-X Gigabit Ethernet over fiber optic cables
802.3ab-1999
1000BASE-T Gigabit Ethernet over twisted-pair cables
802.3az-2010
Energy-Efficient Ethernet
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:
Media Systems
Details
10BASE5
10 megabits per second (Mb/s) transmission speed
“BASE”: Baseband transmission, where the entire bandwidth of the physical medium is exclusively used to transmit Ethernet signals.
500-meter max length
→ Thick Ethernet, using thick coaxial cables for data transmission
10BASE2
10 Mb/s transmission speed
Baseband transmission
185-meter max length (round to 2)
→ Thin Ethernet (Cheapernet), using thinner coaxial cables compared to 10BASE5
10BASE-T
10 Mb/s transmission speed
Baseband transmission
A hyphen, “-”, is used to distinguish the older “length” designators from the newer “media type” designators.
“T”: Twisted-pair wiring (2 pairs, CAT 3 or better)
100BASE-X
100 Mb/s (Fast Ethernet) transmission speed
Baseband transmission
“X”: Use of a blocking encoding scheme
→ Includes both 100BASE-TX and 100BASE-FX, based on the same 4B/5B block signal encoding system
100BASE-TX
100 Mb/s transmission speed
Baseband transmission
Twisted-pair wiring (over 2 pairs of CAT 5 cables)
→ Mostly used variety of Fast Ethernet
100BASE-FX
100 Mb/s transmission speed
Baseband transmission
“F”: Fiber optic cable (multimode)
1000BASE-SX
1000 Mb/s (Gigabit Ethernet) transmission speed
Baseband transmission
“S”: Short-wavelength fiber optic media segments
1000BASE-LX
1000 Mb/s transmission speed
Baseband transmission
“L”: Long-wavelength fiber optic media segments
1000BASE-T
1000 Mb/s transmission speed
Baseband transmission
Twisted-pair wiring (over CAT 5 or better)
It is based on different signal encoding scheme, compared to the above Gigabit Ethernet systems.
10GBASE-SR
10 Gb/s Ethernet transmission speed
Baseband transmission
“SR”: Short-range multi-mode fiber optic cable
10GBASE-LR
10 Gb/s Ethernet transmission speed
Baseband transmission
“LR”: Long-range multi-mode fiber optic cable
10GBASE-T
10 Gb/s transmission speed
Baseband transmission
Twisted-pair wiring (over CAT 6A or better)
40GBASE-SR4
40 Gb/s transmission speed
Baseband transmission
Over 4 short-range multi-mode fiber optic cable
40GBASE-LR4
40 Gb/s transmission speed
Baseband transmission
Over 4 wavelengths carried by a single long-distance single-mode fiber optic cable
100GBASE-SR10
100 Gb/s transmission speed
Baseband transmission
Over 10 short-range multi-mode fiber optic cable
100GBASE-LR4
100 Gb/s transmission speed
Baseband transmission
Over 4 wavelengths carried by a single long-distance single-mode fiber optic cable
1.3 - The Ethernet System
“Man is something that shall be overcome. What have you done to overcome him?” (Thus Spoke Zarathustra, Nietzsche)
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
Note
The Ethernet standard uses “frame”, while “packet” is used to describe the data transmitted at Layer 3 (the network layer), by those who wish to differentiate Layer 2 and Layer 3 functions.
2 - Miscellaneous
Here are more concepts explained!
“Some men see things as they are and say why, I dream things that never were and say why not.” (Robert F. Kennedy, paraphrasing George Bernard Shaw)