OSI reference model PDF

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this document covers description about different layers of osi model and their working....

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OSI MODEL-: OSI stands for Open System Interconnection is a 7 layered framework that was established in 1974 by International Organisation of Standardisation. The model partitions a communication system into abstraction layers. Layers of OSI model:

 PHYSICAL LAYER-: The physical layer is concerned with the following:1. Transfer of bits:-The physical layer is responsible for movements of individual bits from one node to the next. 2. Characteristics of interfaces and medium: the physical layer defines the type of transmission medium and the

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characteristics of the interface between the devices and the transmission medium. Bit rate control: the number of bits sent each second (called transmission rate) is defined by physical layer. Bit synchronisation: the sender and receiver must be synchronised at the bit level. The physical layer provides the synchronization of the bits by providing a clock. Physical topology: the physical layer defines the type of topology that should be used to connect the devices in the network. Ex: star topology, bus topology, mesh topology, ring topology etc. Transmission medium: the physical layer defines the type of transmission medium (simplex, half-duplex or full duplex).

 DATA LINK LAYER Data link is concerned with the following aspects: 1. This layer is responsible for moving frames from one hop (node) to the next. 2. framing 3. Physical addressing: Data link layer adds physical addresses (MAC address) of sender and/or receiver in the header of each frame. 4. Error control: it is provided by means of trailer added at the end of each frame. 5. Access control 6. Flow control

 NETWORK LAYER Network layer is concerned with the following: 1. This layer is responsible to deliver packets from source host to destination host 2. Logical addressing: data link layer adds IP address (logical address) of the sender and receiver in the header of each frame. 3. Routing: data link layer performs routing. Routing is a way to find the most suitable path from source to destination.  TRANSPORT LAYER Transport layer is concerned with following: 1. Service point delivery: transport layer is responsible for the delivery of a message from a specific process on one computer to a specific process on another computer. 2. Segmentation and reassembly: segmentation is the process of dividing a message into segments. Each of these segments contains a sequence number which enables the transport layer to reassemble the message at the destination. 3. Connection control: transport layer provides connectionless and connection orientated services.  SESSION LAYER Session layer is concerned with the following tasks: 1. Session establishment, maintenance and termination 2. Dialog control

3. Synchronisation by adding checkpoints called synchronisation points.  APPLICATION LAYER: It is concerned with the following: 1. Encryption: encryption is the process of converting plaintext into cipher text. In other words, converting a message in human readable form into encoded form so that only authorised parties can access it. 2. Compression: the act of reducing the no of bits is called compression. It is simply done to reduce the size of data. 3. Translation  APPLICATION LAYER 1. This is layer is responsible for providing services to the user. These services include: 2. Network virtual terminal 3. File transfer, access and management 4. Mail services 5. Directory services...