What is the physical layer?
The physical layer, sometimes called the hardware layer, is the first layer in the OSI reference model. As the lowest layer, it’s closely associated with most of the network’s tangible connections – cabling, cabling types and standards, connectors, wireless transmissions, network interface cards, and more. The purpose of the layer is to transfer raw data bits across the physical medium, whether it be wired or wireless. Made up of both software and hardware, the layer acts as a foundation for the most important functions.
In short, this layer is responsible for data transfer over a communication channel. It defines the electrical, functional, and procedural means to activate, maintain, and deactivate a physical link between end systems.
A graphic depicting the location of the physical layer in the OSI model
How does the physical layer work?
Before network communication takes place, you must establish a physical connection to a local area network (LAN). The OSI physical layer can check to see if these cables are properly connected, ensuring successful communication. The layer breaks the frames received from the data link layer into streams of 0s and 1s.
At the receiver end, the physical layer receives data signals, splits them into bits, and passes them onto the next layer as frames. They then travel to the upper layers.
Functions of the physical layer
The physical layer, like other layers of the OSI model, is designed to perform a specific task. In this case, its main task is to transmit data across a connection, which requires electrical, mechanical, and procedural interfaces.
The main functions at the layer include:
Synchronization. The layer performs synchronization of data bits. First, it ensures that both sending and receiving devices are linked, allowing data to transmit and be received in the correct order at the correct rate.
Defining and transmitting bits. The layer provides the means to convert data bits from 0s and 1s. Aside from that, it determines how bits can transmit from the source over communications channels.
Physical topology. Physical topology is the geographical representation of linking devices. Layer 1 defines the layout of devices and cables that make up the network, including the cable, cable pinouts, and connectors used.
Data rate definition. How fast do data bits flow? Layer 1 defines the speed at which bits transmit over the physical link in bits per second.
Clocking. The layer also comes up with a timing mechanism to coordinate data movement from one device to another.
Signal encoding. The physical layer encodes the transferred data into signals that travel over the physical medium, like light and electrical signals.
Line configuration. This defines the physical characteristics of the line, including the type of cable, number of wires, and connector used.
Interface. The layer provides the transmission medium and devices. It also determines the number of network devices to connect.
Device components of the physical layer
OSI model layer 1 is home to a variety of devices used to complete the layer’s functions. Cables and connectors, for example, are a crucial part of the physical layer. Cables carry electromagnetic signals, transmitting them from source to destination. In layer 1, cables used include shield twisted pairs, unshielded twisted pairs, and coaxial cables.
Connectors, on the other hand, facilitate the joining of fiber or electrical cables and conductors. Connector types include fiber optic, USB, Ethernet, and many more. The physical layer also determines the shape and size of the connector.
NICs, or network interface cards, are a hardware component in the physical layer. They are typically in the form of circuit boards, which provide Internet-capable devices like computers with dedicated, full-time network connections.
Receivers and transmitters are also crucial to first layer of the OSI model. Receivers receive signals from the transmission system, whereas transceivers convert electrical signals to light signals and vice versa. They function as radio transmitters and receivers in a single package.