Physical layer co-ordinates the functions required to transmit a bit stream over a physical medium. It deals with the mechanical and electrical specifications of the interface and transmission medium.
The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits. It is responsible for transmitting individual bits from one node to the next.
Functions of physical layer :
- Data Rate –
This layer defines the rate of transmission which is the number of bits per second.
- Interface –
The physical layer defines the transmission interface between devices and transmission medium.
- Representation of Bits –
Data in this layer consist of stream of bits. The bits must be encoded into signals for transmission.It defines the type of encoding i.e.how 0’s and 1’s are changed to signals.
- Line configuration –
This layer connects devices with the medium either it can be point to point configuration or Multipoint configuration.
- Transmission Modes –
Physical layer defines the direction of transmission between two devices such as Simplex, Half duplex, Full duplex.
- Topologies –
Devices must be connected through any topologies either it can be Mesh, Star, Bus And Ring.
Design Issues in Physical Layer :
- The physical layer is basically concerned with transmitting raw bits over a communication channel.
- Mainly the design issues here deal with electrical, mechanical, timing interfaces, and the physical transmission medium, which lies below the physical layer.
- Design issue has to do with making sure that when 1 bit send from one side, it is received 1 bit by other side also not as a 0 bit.
Some questions are here like :
- How many nanoseconds a bit lasts ?
- How many volts should be use to represent a 1 bit and how many for a 0 ?
- How many pins the network connector has and what each pin is used for ?
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