[ACSA Education #3] Physical Media (Devices)

Computer devices use different media to transmit information. Each type of media has different characteristics. Fiber optic media modulates light waves, Wi-Fi modulates radio waves, and copper wire modulates electrical properties such as voltage.

Copper Cable

In the last post, we talked about modulating or changing signals to represent logical data, binary numbers, in Layer 1.
For example, +5V represents a binary “1”, and -5V represents a “0”.

The copper cable commonly used to transmit data on a network is called Twist Pair.
This is because it is made by twisting two pairs of wires together to reduce electromagnetic radiation and interference.

The most common type is Unshielded Twisted Pair (UTP).
For example, in cases such as Filed Twisted Pair (FTP), which is provided to provide protection from external electromagnetic interference (EMI), it is used in very sensitive environments or environments with high EMI levels.

A UTP cable has eight color-coded wires, grouped into four pairs. Two wires are used for transmission (Tx) and two for reception (Rx). The remaining four wires are used to power devices such as phones and cameras using a feature called Power over Ethernet (PoE).

The most common connector used with UTP is the RJ-45 connector. To maintain a data rate of 1 Gbps, the UTP cable cannot exceed 100 m (300 ft) in length.

Fiber Optic

Made of glass or plastic fibers, this media uses optical signals to transmit and receive data.

Light travels down the center of the optical fiber, called the core. The core is surrounded by an optical material called cladding, which traps the light within the core using a technique called total internal reflection.

Optical fiber cables can connect devices over distances longer than 100m of Ethernet UTP and also have higher data transmission rates.
However, distance and speed will vary depending on quality, type of optical fiber, and type of transceiver.
Typically, data transfer speeds are 1Gbps, 10Gbps, 25Gbps, 40Gbps, 50Gbps, 100Gbps, etc.

Optical fibers fall into two groups: multimode (MM) and singlemode (SM). MM is inexpensive for relatively short distances, while SM is more expensive but can support very long distances.

	Multi-Mode Fiber	Single Mode Fiber
Core diameter	50 or 62.5㎛	9㎛
Maximum distance	600m (2,000ft)	40km
Typical data rates	10Gbps	Up to 40/400Gbps
transceiver	LED-based	Laser-based

Multimode (MM) has a core size of 50 to 62.5 μm (micrometers).
This core size allows for increased light harvesting capacity and easier use of low-cost transceivers.
Typical distances are up to 600m and typical data rates are 10Gbps.

If you look at the datasheet for an optical fiber, you will see terms like 50/125 or 62.5/125.
The first number 50, 62.5 represents the diameter of the core, and 125 represents the diameter of the cladding.
50㎛ multimode optical fiber has faster optical transmission speed but shorter distance.

Although the single-mode (SM) core size is only 9㎛, light reflection is reduced because it transmits light directly into the optical fiber.
This means that attenuation (signal strength loss) is reduced and transmission over longer distances is possible.
It is generally suitable for transmission at high data rates such as 40 Gbps or 400 Gbps.

Air / RF (Radio Frequency)

This medium modulates electromagnetic signals, such as amplitude, phase, or frequency, to transmit data. These modulated radio waves are then transmitted through the air. This wireless transmission technology frees us from static wired connections and enables mobility.

Radio frequency (RF) is commonly used to transmit radio, TV, and satellite signals.
However, in computer communications, Wi-Fi is a technology that allows wireless communication between endpoints.

The technology currently operates on two wireless bands: 2.4GHz/5GHz.
Data speeds using Wi-Fi are up to 4.8 Gbps with the latest technology, the IEEE 802.11ax (Wi-Fi 6) standard.
Compared to copper or fiber optic media, Wi-Fi transmission only supports very short distances. The maximum distance between devices is typically between 15 and 30 meters, depending on several factors, including device configuration and the number and type of obstacles.

Full Duplex / Half Duplex

When connecting two or more physical devices to a network, you must consider duplex. A duplex communication system consists of two or more devices connected together, enabling bidirectional communication.
There are two types of duplex systems: full duplex (FDX) and half duplex (HDX).

1. Full Duplex – Both parties can communicate with each other simultaneously.
   A prime example is the telephone. You can talk and listen to each other simultaneously.
2. Half Duplex – Both parties can communicate with each other, but not simultaneously.
   A prime example is a walkie-talkie. When communicating via walkie-talkie, you have to press a button, and if you do, you can't hear the other person.

So in this post, we looked at actual physical devices.

There are many more physical media for communication, but I've only covered the three we use and configure most frequently. I'll post about the rest later, if I get the chance.