Ethernet Overview

Last modified by Microchip on 2024/06/24 11:19

Ethernet is a Data Link and Physical Layer protocol defined by the IEEE 802.3™ Specification. It comes in many flavors, defined by maximum bit rate, mode of transmission, and physical transmission medium:

Maximum Bit Rate (Mbits/s): 10, 100, 1000, etc.
Mode of Transmission: Broadband, Baseband.
Physical Transmission Medium: Coax, Fiber, UTP, etc.

OSI Model Basics

One of the things that have made Ethernet so widely adopted is the Open Systems Interconnection (OSI) model. OSI is a model of the many layers involved when two intelligent devices share information. With this model, you, as the developer of the Application Layer, do not need to know about the physical medium that data is being transmitted on, you can just focus on presenting the data. The OSI model has seven layers, but TCP/IP reduces these to five.

Here, the OSI model is mapped to the Internet Engineering Task Force Transmission Control Protocol/Internet Protocol (TCP/IP) (Software) and Ethernet (Hardware) realities.

The "Medium" is not considered part of the OSI model, however, it falls within the IEEE 802 specification and forms the basis for naming all of the Ethernet Families.

OSI model

Ethernet Families

The Ethernet physical layer has evolved over time to utilize several media interfaces and transmission speeds.

Physical Media	Speeds
Co-axial Twisted Pair Fiber-Optic	1 Mbps 10 Mbps 100 Mbps 1000 Mbps 10 Gbps 100 Gbps

Ethernet Family Naming Scheme

Ethernet families are named according to certain medium specifications:

For example, Fast Ethernet is named:

Bit Rate

The nominal usable speed for the MAC layer.

Examples:

10, 100, 1000 (no suffix = megabits/second)
10G (G suffix = gigabits/second)

Signaling Type

BASE - Baseband signaling (most common type)
BROAD - Broadband signaling
PASS - Passband signaling

Medium

T = twisted pair
C = copper/twinax
F = fiber (various wavelengths)
S = 850 nm short wavelength (multi-mode-fiber)
L = 1300 nm long wavelength (mostly single-mode-fiber)

PCS Encoding

Certain bit encoding schemes are employed at certain speeds to reduce the required transmission bandwidth.

X = 8b/10b block encoding (Gigabit ethernet) or 4b/5b (Fast Ethernet)
R = 64b/66b for large blocks (10G ethernet)

#Lanes

Refers to the number of signal-carrying wires (or wire pairs) used per link (1, 2, 4, 10).

Common Families Supported by Microchip

Family Type	Medium	Data Rate	Segment Length
10BASE-T	UTP (Unshielded twisted pair)	10 Mbps	100 m
100BASE-TX	2-Pair CAT5 UTP	100 Mbps	100 m
100BASE-FX	2 Optical Fibers	100 Mbps	100 m
1000BASE-T	4-Pair CAT5 UTP	1000 Mbps	100 m