Physical Layer in OSI Model

Physical Layer is a layer in the OSI Model that transmits raw bits over a physical medium. The following are the roles of physical layer in OSI Model,

Physical Layer in OSI Model


The transmission medium and interface between the devices and the medium.

Transmission Modes

Transmission mode in Computer Networks is the transfer of data between two devices and it defines the direction of signal flow between them.  Modes includes, Simplex, Half-duplex, and Full duplex.

Simplex Transmission Mode

Simplex mode is a mode when one device always acts as a sender and another always act as a receiver. It means the direction of signal flow is the same i.e. unidirectional.

For example, Mouse and monitor, Mouse for input, whereas Monitor for receiving output.
Another example can be, Keyboard and Monitor

Half Duplex Transmission Mode

Half Duplex mode is a mode when either of the device acts as a sender or a receiver, one at a time.

For example, communication between a walkie-talkie, wherein at a time only one radio on the channel can transmit. After receiving the message, another radio on the channel replies. This means only one person can talk at a time. It is a two-way radio.

Full Duplex Transmission Mode

Full Duplex mode is a mode in which both sender and receiver can transfer simultaneously.

For example, when you are having a conversation with anyone on mobile phone, then you can speak and hear at the same time i.e. simultaneously.

Line Configuration

The Physical layer connects devices to the medium.

Two or more devices should be connected to the same physical communication pathway, so that there is successful transfer of data. This communication pathway is called a line.

Line configuration is a way two or more devices attached to a link for communication.

Point-to-Point Line Configuration

A dedicated link is provided by point-to-point configuration between two devices. For example, TV Remote, for changing channels. An infrared ray is used for establishing communication between remote control and TV.

Multipoint Line Configuration

More than two devices share a link in multipoint line configuration. It can be of two forms,

  • Spatially shared line configuration, if these devices use the link simultaneously.
  • Time shared line configuration, if it takes turn to use.


The data is in the form of stream of bits, which must be encoded into signals for transmission.


The connection of devices to make a network is called a Topology. It includes mesh, ring, bus, and star topology.

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Data Link Layer in OSI Model
Network Layer in OSI Model
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