Physical Layer in OSI model

Physical layer in OSI
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The following article provides all information related to Physical Layer in OSI model. Also it includes data encoding, synchronization techniques as well as components of Physical Layer in OSI model.

OSI Layers:

There are seven layers in this OSI model layer and each layer interacts with each other.

In this the first and second layer are called media layer and layer 3, 4, 5, 6, and 7 are called host layers.


Physical Layer

This physical layer is the lowest layer of the OSI Model, and is solely concerned with the transmission and reception of unstructured raw bit streams over a physical medium.

It describes electrical/optical, mechanical, and functional interfaces in its physical medium, and also carries signals to all higher layers.

Physical layer only defines cables, network cards and physical aspects.

It makes the actual physical connection between devices. Such physical connection can be made using twisted pair cable, fiber-optic, coaxial cable or wireless communication media.

Data Link layer send frames to this layer and converts them into signals that are compatible with other transmission media.

For example, if a metallic cable is used, then it will convert the data into electrical signals; Whereas if a fiber optical cable is used, then it will convert the data into luminous signals; If a wireless network is used, it will convert the data into electromagnetic signals; And it will continue like this.

When receiving data, this layer receives that signal and converts them into 0s and 1s and then sends them to the Data Link layer, which then puts those frames back together. and then check its integrity.

These X.25 protocols work in physical, data link, and network layers.


What are the functions of physical layer:

Data Encoding:

This modifies the simple digital signal pattern (1s and 0s) used by PCs to better accommodate the characteristics of the physical medium, including bit and frame synchronization. Aid too.

This determines that:
1. Does the signal state represent a binary 1?
2. How does the receiving station know when a “bit-time” starts.
3. How this receiving station delimits a frame.


Transmission Technique:

Determines whether the encoded bits are transmitted via baseband (digital) or broadband (analog) signaling.


Physical Medium Transmission:

It transmits bits in electrical or optical signals that are appropriate for the physical medium, and determines:
1. Which physical medium options can be used.

Protocols that are used in the physical layer are ISDN, IEEE 802 and IEEE 802.2.

  • Bit synchronization:

This physical layer provides synchronization of the bits, for which they use a clock. This clock controls both transmitter and receiver so that it provides synchronization in bit level.

  • Provides physical characteristics of interfaces and medium:

Physical layer manages how a device connects with network media.

For example, if a device’s physical connection uses coaxial cable to connect to the network, then the hardware that performs the functions in the physical layer should be designed in such a way that it can work in a specific type of network.


All components including connectors are specified in the Physical Layer.

  • Bit rate control:

It defines the duration of a bit.

  • Line Configuration:

Physical layer again defines how devices should be connected with the medium.

It uses two different line configurations that is point to point configuration and multipoint configuration.

It is used to activate, maintain and deactivate the physical connection.

  • Transmission mode:

Physical layer defines how data flows between two connected devices.

The various transmission modes that can be possible in this are –

Simplex, half-duplex and full-duplex.

  • Physical topologies:

Physical layer specifies how different, devices/nodes are arranged in a network i.e. bus, star or mesh.

  • Multiplexing:

Physical layer can use different techniques in multiplexing, so that channel efficiency can be improved.

  • Circuit switching:

Physical layer also provides how to interconnect with other networks by circuit switching.


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