Network Cabling:

there are three types of network cabling:

• Co-axial
• Twisted Pair
• Fiber Optic

At its core, data transmission through these cables happens through signals. In copper-based cables like coaxial and twisted pair, data is transmitted as electrical signals, representing binary data (0s and 1s) through variations in voltage. In contrast, fiber optic cables use pulses of light, enabling much higher speeds and longer distances with minimal signal loss.

However, simply sending signals is not enough. For devices to communicate effectively, there must be a set of rules that define how data is formatted, transmitted, and interpreted. These rules are known as protocols, and they ensure that devices can understand each other, even if they are built by different manufacturers.

To make communication consistent and reliable, networking standards define the rules (protocols) that control how data is structured and transmitted over a physical medium.

One of the most widely used standards for wired networking is Ethernet, which defines how data is packaged, addressed, and transmitted across network cables.

What is Ethernet?

Ethernet is a networking standard used in Local Area Networks (LANs) to enable communication between devices over a wired connection.

It defines how data is structured, addressed, and transmitted so that devices within a network can communicate reliably, regardless of the manufacturer or device type.

Ethernet forms the backbone of most wired networks, connecting devices such as computers, switches, routers, and wireless access points.

What Does Ethernet Actually Do?

At its core, Ethernet does three main things:

1. Packing (Framing)

Ethernet takes raw binary data and organizes it into structured units called frames. This ensures that data can be clearly separated and understood during transmission.

2. Labeling (Addressing)

Each frame is assigned:

A source MAC address A destination MAC address

These addresses uniquely identify devices within a local network and ensure data reaches the correct destination.

3. Transporting (Transmission)

Ethernet defines how these frames are transmitted over physical media such as copper cables or fiber optics, using electrical or light signals.

It also includes mechanisms for error detection to ensure data integrity.

How Ethernet Actually Works Under the Hood

Up to this point, we’ve understood that Ethernet defines how data is structured into frames and transmitted over cables. However, an important question arises:

If data is ultimately transmitted as electrical or light signals, where do Ethernet frames exist?

To answer this, we need to introduce the concept of the device that actually implements Ethernet.

The Role of the Network Interface Card (NIC)

Every device connected to a network—whether it’s a computer, server, or switch—uses a
Network Interface Card to communicate over the network.

The NIC is the hardware component responsible for implementing Ethernet’s rules.

While Ethernet is a standard (a set of rules), the NIC is the physical component that follows those rules.

From Data to Signals (Sending Side)

When a device sends data, the process happens in stages:

1. Application generates data
   For example, a browser creates a request to load a website.

2. Data reaches the NIC
   After passing through higher-level protocols, the data is handed over to the NIC.

3. Ethernet framing happens inside the NIC
   The NIC organizes the data into an Ethernet frame:

   | Preamble | Destination MAC | Source MAC | Type | Data | CRC |
   

4. Frame is converted into signals

   The NIC converts this binary frame into:

   • Electrical signals (for copper cables), or
   • Light pulses (for fiber optic cables)

5. Signals travel through the cable
   These signals carry the encoded Ethernet frame across the network.

What Actually Travels in the Cable?

It is important to understand:

The cable does not carry “raw, unstructured bits.”
It carries signals that represent a fully constructed Ethernet frame.

In other words, the structure defined by Ethernet already exists before transmission, and the physical medium simply carries it in encoded form.

From Signals Back to Data (Receiving Side)

On the receiving device, the process is reversed:

1. NIC receives signals
   Electrical or light signals arrive via the cable.
2. Signals are converted back to bits
   The NIC reconstructs the binary data.
3. Ethernet frame is interpreted
   The NIC:
   • Detects the start of the frame (preamble)
   • Reads the destination MAC address
   • Verifies data integrity using CRC
4. Data is passed upward
   If the frame is valid and intended for the device, the payload is passed to higher-level protocols.

Ethernet vs Physical Transmission

This leads to an important distinction:

• Ethernet does not transmit signals directly
• Ethernet defines how data is structured into frames

The actual transmission is handled by the physical layer, which converts those frames into signals.

A Clear Mental Model

To simplify:

• Ethernet = rules (how data is structured and interpreted)
• NIC = implementation (hardware that applies those rules)
• Cable (copper/fiber) = medium (how signals are carried)

Understanding this separation helps clarify:

• Why different cable types (copper vs fiber) can still use Ethernet
• Why devices from different manufacturers can communicate seamlessly
• How data maintains its structure even when converted into signals

Key Takeaway

Ethernet does not act on signals directly. Instead:

Ethernet defines how data is packaged into frames before transmission and how those frames are interpreted after reception, while the NIC handles the actual conversion between frames and physical signals.