What Is the Physical Layer: A Beginner’s Guide

Understanding the physical layer is essential to grasp the intricacies of communication between network devices. Whether you want to pursue a career in network communications or boost your home network, understanding the OSI model and the role the physical layer plays can help you make informed decisions about your network topology, hardware choices, and more.

Read more: 7 In-Demand IT Skills to Boost Your Resume 

What is the Open System Interconnection model?

The Open System Interconnection (OSI) model framework contains seven distinct layers, including the physical layer. Each layer is responsible for a different aspect of the communication system, and together, these layers allow devices to exchange data, information, and communication across servers. The physical layer is the first layer within this model, and many consider it the most rudimentary. 

Starting with the physical layers helps you understand the foundation of network communications before moving on to additional layers, allowing you to gain a deeper understanding of the OSI model. 

What is the physical layer?

The physical layer transmits and receives data (or bits) over physical mediums, such as copper cables, fiber optic cables, wireless radio frequency signals, or other channels. As the name suggests, this type of OSI model layer typically deals with the physical aspects of the communication system, such as cabling, connectors, and signal encoding. This layer is the foundation for the remaining layers and provides a data signal conversion and transmission framework. When using wireless networks, the physical layer transmits data using radio frequency signals with the help of routers, access points, and wireless network adapters. These devices convert digital data into radio frequency signals that other devices receive.

Higher layers in the OSI model rely on the physical layer for data transmission, and each additional layer within the model adds complexity. For example, Layer 2 is the data link layer, which detects and corrects errors, as well as organizes the data into frames. As the layers increase, communication is able to be routed, segmented, and managed with more complexity.

Physical layer hardware examples

The physical layer may utilize different hardware components depending on the type of network configuration and data transmission requirements. Common types of physical layers and their functions include the following:

• Twisted pair cables: For Ethernet or telephone line connections

• Coaxial cables: For cable television and broadband internet

• Fiber optic cables: For high-speed or large data transmission

• Network interface card: For connecting computer hardware to computer networks

Physical layer topology

The topology of a physical layer is the arrangement of network devices. You can work with five physical topologies, including the following.

Read more: Network Topology: Types and Uses

Star topology

Star topology is a network topology characterized by all devices connecting to a single central device or node. This central node can be either a switch or a hub that transmits data between the devices. This type of topology can be beneficial because it is robust against single cable failure.

Mesh topology

Mesh topology connects each device to all other devices within the network. This type of system can prevent congestion in communication between devices because it provides a dedicated path between each device in the system. It also provides easy scaling, enabling devices to add without disrupting current communication channels. However, this type of topology can be more challenging to install because of the higher number of inter-device connections.

Bus topology

Bus topology connects multiple devices along a single cable that acts as the “spine” of the system. It can be cost-effective compared to other topologies, but it can also lead to privacy issues because all devices use the same communication line. In addition to this, adding or removing devices poses challenges as it disrupts the current system.

Ring topology

Ring topology connects all devices along a circular path. Devices can transmit data to devices on either side of them through the ring. This type of topology has relatively easy installation, but expansion or disruptions can affect all devices in the system..

Wireless topology

Wireless topologies don’t need physical cabling between devices, which prevents disruptions due to cable breaks or installation of new devices. This type of topology is especially useful for remote users and easily scales to accomodate more devices on the network. However, this type of system has certain security concerns, and can have higher latency than wired topologies. 

Attributes of the physical layer

You can characterize the functions of the physical layer into several categories, making it an integral part of the OSI model. Several standard attributes for physical layers include:

1. Data signal conversion

The physical layer converts data to either an analog or a digital signal. Analog signals are continuous waveform signals, while digital signals transmit through discrete network pulses.

2. Data transmission

To communicate data between devices, you must use wired or wireless mediums. Wired mediums include physical media such as cables, and wireless mediums include wireless networks such as Wi-Fi or Bluetooth.

Data can be transmitted in one of three modes. Simplex mode means that only one device receives data while the other sends it. For example, keyboards transmit data, but they do not receive it. Data can also be transmitted in half-duplex or full-duplex mode. Half-duplex mode allows both devices to send and receive data, but they cannot do this simultaneously, such as with a walkie-talkie. Full-duplex mode enables both sending and receiving data at the same time, such as with messaging systems and telephones.

3. Data modulation

Data modulation is the way digital data maps onto the carrier signal for transmission. Amplitude-shift keying, frequency-shift keying, and phase-shift keying are standard modulation techniques that can maximize available bandwidth while reducing noise interference with the data. 

Services that physical layers provide

​​The physical layer is the foundation of any computer network, providing the means for data transmission across various mediums. This layer is responsible for several key tasks that enable raw data transfer between devices. The main services of the physical layer include the following:

• Maintaining the rate of data flow

• Synchronizing bits

• Controlling bit rate

• Processing physical signals

• Directing data transfer

• Deciding network topology

• Providing inter-device interfaces

• Providing data modulation

• Connecting computer software to the external network

• Forwarding error correction

Limitations of physical layers

To understand the function of physical layers, it's helpful to understand its limitaitons. While physical layers often involve transmission along physical mediums, they do not include the installation or production of the physical layers themselves. 

In addition, physical layers are not responsible for data formatting, session initiation, data encryption or other security, or resource allocation. These tasks rely on other layers within the OSI model.

Examples of protocols using physical layers

Several widely used protocols rely on the physical layer to transmit data effectively. When working with physical layers, you may encounter the following protocols:

• Controller area network: This type of communication protocol is common in automotive and industrial industries.

• Ethernet: This is a local area networking protocol.

• Digital subscriber line: This protocol delivers high-speed, high-bandwidth internet across telephone lines.

• Universal Serial Bus (USB): This protocol commonly helps connect devices to computers. 

• Bluetooth: This communication protocol allows low-power, short-range wireless communication.

Read more: Information Technology (IT) Terms: A to Z Glossary

How to start building skills in physical layers

Getting started with physical layers requires a basic understanding of electronics and circuitry. You can begin with a few steps to build a strong foundation in electronics and computer systems, including the physical layer.

1. Learn the fundamentals: You can start by learning the basics of electronics, including voltage, current, resistance, and capacitance, through online courses like those offered on Coursera.

2. Learn about communication protocols: Communication protocols are essential to understanding how physical layers work. Learn about protocols like Ethernet, USB, and Bluetooth and how they interact with physical layers by taking courses or reading textbooks.

3. Experiment with hardware: You can gain firsthand experience by building circuits and experimenting with hardware. Start slow with beginner-friendly projects, gradually working your way up to more complex designs. You might start with a simple circuit, before experimenting with building a network and connecting various devices. 

Entry-level IT roles

Entry-level careers that deal with physical layers include positions like a network technician or network specialist. These positions typically require related educational experience (associate or bachelor’s degree) or equivalent vocational training in electronics or a related field.

Read more: 6 Network Certifications for Your IT Career

Get started with Coursera

The physical layer is the first layer of the OSI model and includes the physical hardware required to connect your device to computer networks. By understanding its components, such as the topology, hardware, and functions, you can deepen your understanding of how computer systems work.

If you're interested in physical layers, you can learn about various networking concepts, cabling standards, and protocols through courses offered on Coursera. Consider courses like The Bits and Bytes of Computer Networking, or round out your digital skills with the Google IT Support Professional Certificate.