What are the different layers of OSI model?

OSI Model :

ISO – OSI model (Open systems interconnection model) consists of 7 layer :
  • Physical layer 
  • Data link layer 
  • Network layer
  • Transport layer 
  • Session layer
  • Presentation layer
  • Application layer

osi model

Physical Layer :
  • It deals with the functionalities required to transmit a bit stream over a physical medium.
  • Transmission unit is Bits
  • It is responsible for movements of individual bits from one node to the next.
  • It defines the characteristics of the interface between the devices and the transmission media.
  • It defines how the bits are encoded into electrical or optical signals
  • It also controls Data rate and synchronization of bits
  • It also defines the Network Topology and transmission mode.
Data Link Layer :
Its functions include –
  • Framing : It divides the stream of bits received from the Network Layer into manageable data units called Frames.
  • Physical Addressing : Adding header to the frame to define the physical address of the sender or receiver of the frame.
  • Flow Control : If the rate at which the data is absorbed by receiver is less than that of sent from the sender, flow control mechanism is used to prevent the loss of data.
  • Error Control : DLL adds functionality to detect and re-transmit the damaged, lost or redundant frames.
  • Access Control : DLL helps in controlling the access to the shared channel.
  • Transmission unit is Frames
Network Layer :
  • It is responsible for the source to destination delivery of a packet possibly across multiple network, from Host to Host.
  • It ensures the correct delivery of packet from origin to final destination
  • Logical Addressing : Physical Addressing handles the addressing problem locally.If a packet passes the Network boundary, logical addressing is used to distinguish the source and destination.
  • Routing : Routers are used to route the packets from source to their destination.
  • Transmission unit is Packets
Transport Layer : 
  • It is responsible for source to destination delivery of entire message.
  • It may create connection between the source or destination.
  • Service point Addressing Layer : End to end delivery means the delivery of packet from specific process from one system to specific process on another. Thus, its header contains a service-point address or port address.
  • Segmentation and Reassembly : A message is divided into transmittable segments , each containing a sequence number which enables it to reassemble at the delivery end.
  • Connection Control : Connection made can be Connection-less or Connection oriented.
  • Flow Control and Error Control is also supported.
  • Transmission unit is Segments
Session Layer :
  • It establishes , maintain and synchronizes the interaction between communicating system.
  • Transmission unit is Data or message
  • Dialog Control : It allows communication to happen either in Half-duplex or Full duplex mode.
  • Synchronization  : Adding checkpoints into a stream of data to synchronize the communication or transmission.
Presentation Layer : 
  • Concerned with syntax and semantics of the information exchanged.
  • Translation : Changes the data from sender dependent format to common format.
  • Encryption/Decryption
  • Compression
Application Layer :
  • It provides user interface and support services such as e-mail, remote access etc.
  • It consists of various protocols needed by users like HTTP, FTP

Leave a Reply

Your email address will not be published. Required fields are marked *