(also layer 1)
Physical layer definition
The physical layer is the first and lowest layer in the Open System Interconnection (OSI) model. The physical layer controls how raw bits of data are transmitted over a physical medium. For this purpose, it deals with electrical and physical device specifications, such as connector types, cable length, and signal strength requirements.
Real physical layer functions
- Connections to communications media: The devices on the physical layer must be made compatible and be able to communicate with each other. The physical layer is responsible for providing a standardized interface to the transmission medium, including specifying any mechanical or electrical requirements.
- Bit-by-bit delivery: Data in the physical layer consists of bits, which must be encoded into signals for transmission. The physical layer also defines the rate of transmission (measured in bits per second) and the data transmission mode — simplex (transmission in one direction only), half-duplex (transmission in one direction at a time), or full-duplex (transmission in both directions at the same time).
- Synchronization: The sender and receiver on the physical layer must be synchronized at bit level for data transmission.
Examples of technologies with physical layers
- ARINC 818: Avionics Digital Video Bus
- CAN bus
- Ethernet physical layer varieties
- IEEE 802.15.4
- Low-voltage differential signaling
- Mobile Industry Processor Interface
- Modulated ultrasound
- OTN (Optical Transport Network)
- Telephone network modems
- PCI Express
- 802.11 Wi-Fi