OSI Model: Physical Layer and its Function

In OSI model, physical layer is first and lowest layer. Physical layer coordinates all the functions that are required to carry bit stream over a transmission media. The transmission media may be either guided or unguided media. The physical layer deals with the mechanical and electrical specification of transmission media. 

The physical layer defines functions and procedures to transmit data over transmission media.

Functions of Physical Layer

Representation of Bits: Data in physical layer consists of bit stream. To transmit data, bits must be encoded into signals either electrical or optical. Physical layer defines the type of encoding, how 0s and 1s are changed into signals.

Data rate: Physical layer defines data rate mean numbers of bits sent per second.

Synchronization of Bits: The data rate may be different on sender side and receiver side. But, for transmission sender and receiver must be synchronized at bit level. The sender and receiver clocks must be synchronized.

Physical Characteristics of Interfaces and Medium: The physical layer defines the type of transmission medium and characteristics of interface between the devices and transmission medium.

Line Configuration: The physical layer defines connection of devices to the media. In point-to-point configuration, two devices are connected through a dedicated link. In multipoint configuration, multiple devices connected through a link.

Topologies: Physical layer defines how devices make a network using topologies: Mesh, Star, Ring, Bus or Hybrid.

Transmission Mode: Physical also Layer defines the direction of transmission between two devices: Simplex, Half Duplex or Full Duplex.