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
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.
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