Physical layer

In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer. It deals with the physical connection between devices. This layer is very important because it handles how data moves through wires, cables, or other media.

The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium. This means it decides the shapes and properties of electrical connectors, the frequencies to transmit on, the line code to use, and other low-level details needed for communication.

At the electrical layer, the physical layer is often implemented in a special chip called a PHY chip. In the world of electronic design automation (EDA), it is created using a design block. In mobile computing, many devices use the MIPI Alliance *-PHY family of interconnect protocols to help them communicate efficiently.

Role

The physical layer is the first part of a network that helps devices connect together. It decides how to send information as signals over wires or other paths. This layer changes bits of data into signals that can travel between devices.

It includes the electronic parts that make this happen and works with the next level of the network to send and receive these signals. The physical layer supports the higher levels that put data into packages for sending.

Physical signaling sublayer

In a network using Open Systems Interconnection (OSI) architecture, the physical signaling sublayer is part of the physical layer. It connects with the data link layer's medium access control (MAC) sublayer. It helps with encoding symbols, sending and receiving data, and decoding the information, as well as keeping electrical separation between parts.

Relation to the Internet protocol suite

The Internet protocol suite is a set of rules used for the Internet and similar networks. It focuses on how data moves across the network but does not include details about the physical connections between devices, unlike the model that deals with hardware.

Services

The physical layer helps devices send data bit by bit or symbol by symbol over a connection. It sets standards for how connectors and cables should look and work, including details like cable length and signal strength. It handles things like making sure signals don’t interfere with each other and managing how data flows between devices.

It also decides how to turn data into electrical signals and manages how devices share the connection. To make sure data arrives correctly, it can use special techniques to fix errors. Other topics include how fast data can go, how devices are arranged, and how they talk to each other.

PHY

"PHY" redirects here. For other uses, see PHY (disambiguation).

A PHY, short for physical layer, is an electronic circuit, often built as a single chip, that helps devices connect to each other. It works with the first layer of the OSI model, which deals with the actual wires or signals used to send information.

A PHY connects a device that manages data (often called MAC) to a physical medium like an optical fiber or a copper cable. It includes parts that handle how data is coded and sent over the medium.

Ethernet physical transceiver

The Ethernet PHY is a part that works with the physical layer of the OSI network model. It helps send and receive Ethernet signals. It connects the analog signals used by Ethernet to the digital parts of a system that handles higher-level tasks. It usually works with a special interface called media-independent interface (MII) to connect to a chip that manages data.

Common Ethernet connections use fiber or several copper wires, but newer types like Single Pair Ethernet (SPE) can work with just one pair of wires. Examples of PHYs include chips from companies like Texas Instruments, Marvell, and others.

Other applications

• Wireless LAN or Wi-Fi: The PHY part handles radio signals and digital processing for wireless connections. These parts are often combined with the layer that manages access to the medium in a single chip. Other wireless uses include 3G/4G/LTE/5G, WiMAX, and UWB.
• Universal Serial Bus (USB): Most USB devices include a PHY chip that connects the digital and signal parts of the interface.
• IrDA: The Infrared Data Association has a specification for the physical layer called IrPHY.
• Serial ATA (SATA): Controllers for SATA use a PHY.
• PCI Express (PCIe): Controllers for PCIe use a PHY.

Technologies

The physical layer connects devices using different technologies. Some of these technologies include:

• 1-Wire
• ARINC 818 Avionics Digital Video Bus
• Bluetooth physical layer
• CAN bus (controller area network) physical layer
• DSL
• EIA RS-232, EIA-422, EIA-423, RS-449, RS-485
• Etherloop
• Ethernet physical layer Including 10BASE-T, 10BASE2, 10BASE5, 100BASE-TX, 100BASE-FX, 1000BASE-T, 1000BASE-SX and other varieties
• G.hn/G.9960 physical layer
• GSM Um air interface physical layer
• UMTS air interface physical layer
• LTE air interface physical layer
• 5G air interface physical layer
• Communications satellite technologies physical layers
• IEEE 802.15.4 physical layers
• IEEE 1394 interface
• IRDA physical layer
• ISDN
• ITU Recommendations: see ITU-T
• I²C, I²S
• LoRa
• Low-voltage differential signaling
• Mobile Industry Processor Interface physical layer
• Modulated ultrasound
• Optical Transport Network (OTN)
• SMB
• SONET/SDH
• SPI
• T1 and other T-carrier links, and E1 and other E-carrier links
• Telephone network modems — ITU-T V.92
• TransferJet physical layer
• USB physical layer
• PCI Express physical layer
• 802.11 Wi-Fi physical layer
• Visible light communication co-ordinated under IEEE 802.15.7
• X10