The Physical Layer of OSI Model


The Physical Layer of OSI Model

The Physical Layer

  • Physical Layer is first layer of OSI model.
  • It's main function is to carry a bit stream over a Physical medium.
  • One of the major functions of Physical Layer is to transmit data in the form of electro-magnetic signals across a transmission medium. Whether we are collecting numerical static from another commuter, sending animated pictures from design workstation we do transmit data across network connection. This is done by physical layer .
  • Figure shows a position of a Physical Layer with respect to the transmission medium and the data link layer. In this Data Link Layer consist of a bit of frame like 0101 etc for the transmission so we need to convert it into signal and this important role play by physical layer. It takes frame from Data Link Layer convert it into signal and transmitted it using transmission media and again receiver side decode it to digital type like 0101 etc.
  • In the depth there are many parameter we need to count to transmit a data or convert it into signal like how we representation of bits in says that it’s consist of a stream of bit with no interpretation. In this its transmitted data into either electrical or optical signal.
  • Second thing is transmission rate. It’s says that how much bit send per second. So physical layer defines duration of a bit how long its carry bit .its depend on these factor the level of signal we use, the bandwidth available, quality of channel.
  • Physical layer use two types of transmission mode to transmit a data one is parallel and second is serial. In serial also many types like Asynchronous, synchronous, isochronous.
  • Now if we sending a bit its might be possible receiver have not the same bit rate as a sender bit rate so physical layer provide facility to synchronies a bit rate.
  • Physical layer use topology: its means that how device connected to each other. there are many topology like mesh topology in which every device connected to every other device.

Star topology in which device are connected to a central device.

Ring topology in which each device connected to a next device make a ring type.

Bus topology in which every device on a common link.

And hybrid topology in which it’s a combination of two or more topology.

Transmissions mode: Physical layer also give a information in which two device transmitted. There  are three types:

  1. Half duplex: In this both device transmit data but one at a time.
  2. Full Duplex: in which two devices can send and receive data at a same time.
  3. Simple: in this only one device can send and other is only receiving data.
  • Physical layer use transmission media in which it may be wired or wireless. If its use wire it may be twisted pair is consist of two conductor, coaxial cable has a central core conductor or fiber optic cable made of glass or light and transmit signal in form of light. and In wireless it might be ground propagation, sky propagation.

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