Physical Layer of the OSI Model: Definition

Physical layer is the first or the bottom most layer of the OSI model. This layer is used to establish or terminate a connection to a communication medium. It also defines the electrical and mechanical specifications like cables, connectors and signaling options of the medium

Physical layer receives data from the upper layer called the data link layer. It converts the received data into bit system. The data is then transmitted through the medium to the receiver. At the receiving end, physical layer receives the data in bit format. It forwards the data to the data link layer. 

Responsibilities of the physical layer:

Characteristics of media - defines the characteristics of the interface which used for connecting the devices. It also define the type of the transmission media such as copper wire or fiber optic cable

Encoding – define the encoding type .encoding means changing bit stream (0s and 3s) into signal. Before transmission, physical layer encodes the signal into electrical or optical from depending upon the media

Transmission Rate – defines the transmission rate of bits. This provides number of bits transmitted per second. It defines how long will the duration of a bit be.

Transmission Mode – defines the transmission mode between two devices transmission mode specifies the direction of signal flow. The different types of transmission modes are:

☼ Simplex – communication is done only in direction. One device can only send and the other can only receives.

☼ Half duplex – communications is done in both the directions but not at the same time

☼ Full duplex - communications is done simultaneously in both the directions at the same time 

Topology – defines how the devices are connected to from a network