Open system Interconnection (OSI) model was developed by the international standards organization (ISO) describes the flow information from one computer to another. OSI model is also called ISO OSI reference model. It is conceptual model that has seven layers

  • application layer
  • presentation layer
  • session layer
  • transport layer
  • network layer
  • data link layer
  • physical layer

Physical layer

 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 info bit stream. 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


  • Characteristics of media :- Defines the characteristics of the interface which is used for connecting the devices. It also defines the type of the transmission media such as copper wires of fiber optic cables.
  • Encoding : Defines the encoding type. Encoding means changing bit stream 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 bit. 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 –
  1. Simplex :- Communication is done only in one direction. one device can only send and the other can only receive.
  2. Half duplex :- Communication is done in both the direction but not at the same time.
  3. Full duplex :- Communication is done simultaneously in both the directions at the same time.

Data link layer

Data link layer is the second layer of OSI model. it handles data transfer between network and the physical layers. Data unit at the data link layer is called as frame. data link layer receives data from network layer. it adds header and trailer to the data and passes data to the physical layer. At the receive side, data link layer receives data from the physical layer. It detaches Header and Trailer rom the data and passes data to the network layer.  


  • Framing :- The physical layer delivers raw bits from the source to destination. during transmission, the value of the bits can change. It is also possible that the number of bits received by the receiver may be different from the number of bits send by the sender. To resolve the problem, The data link layer organizes the bit into manageable data unit called as frames.
  • physical addressing :- Data link layer adds header to the frame which contains the physical address of the sender of the sender or receiver. Headers are assigned when the frames are to be distributed various systems within the network.
  • Error Control :- Another function of the data link layer is error control. Error control detects and corrects errors. During transmission, If a frame,  If a frame is lost or corrupted, The data link layer retransmits  that frame. It also prevents duplicates of frame. It also prevents duplication of frame. Error control is accomplished using trailer at the end of the frame.