What is the Physical Layer?

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  • Written By: Troy Holmes
  • Edited By: W. Everett
  • Last Modified Date: 05 November 2019
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Computer networks are designed based on standard protocols and communication layers. These network standards are typically derived from the open standards interconnection model (OSI). Each layer within the communication standard is designed for a specific purpose and process. The physical layer is actual wire hardware layer of the communication network. This layer defines the wire pinning configuration standards and physical design for the copper wires in the network cables.

When a computer message is sent over the physical layer, it requires a special encoding process. This is where the computer information is transformed from bits of data into electronic signals that are interpreted through network hardware. It is considered the lowest level of the network stack because it is responsible for sending the actual message over the network hardware device.

Each type of network design has a specific frequency and protocol. A network cable is responsible for converting communication into electronic signals. The physical layer defines the specification for the electronic signal that is transmitted through the network cable. This includes the predefined frequency and cable length that ensures proper communication between devices.

The physical layer is not limited to a copper wire configuration. It also includes wireless and fiber optical specifications. The definition is intended to outline how computer programs should transmit messages between computers using specific frequencies and protocols.


In addition to the transmission protocol, the physical layer also defines how to properly receive a message. This defines how a network device should interpret signals from another device on the network. Both the sender and receiver of messages need to follow the protocols to ensure acceptance of data packets passed over the network.

The network protocol is similar to a telephone system. A specific wire is used for a headset, while another wire is used for the microphone. Within a network, messages are transmitted over a specific frequency and received by the monitoring device. Once the message is received, a response message is sent to the transmitting device acknowledging the receipt of the message.

The physical layer also includes standards on ensuring message quality and acceptance by the receiving device. Clock recovery is an example of a standard for acknowledging receipt of messages within the physical layer. The clock recovery system is a predefined time within which a message must be received and responded to within the network. If the receiving application does not submit an acknowledgment message within a predefined duration, the sending device assumes the message failed.


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