OSI 7 Layers Reference Model For Network Communication
Open Systems Interconnection (OSI) model is a reference model developed by ISO (International Organization for Standardization) in 1984, as a conceptual framework of standards for communication in the network across different equipment and applications by different vendors. It is now considered the primary architectural model for inter-computing and internetworking communications. Most of the network communication protocols used today have a structure based on the OSI model. The OSI model defines the communications process into 7 layers, which divides the tasks involved with moving information between networked computers into seven smaller, more manageable task groups. A task or group of tasks is then assigned to each of the seven OSI layers. Each layer is reasonably self-contained so that the tasks assigned to each layer can be implemented independently. This enables the solutions offered by one layer to be updated without adversely affecting the other layers.
The OSI 7 layers model has clear characteristics. Layers 7 through 4 deals with end to end communications between data source and destinations. Layers 3 to 1 deal with communications between network devices.
The specific description for each layer is as follows:
Layer 7:Application Layer
Defines interface to user processes for communication and data transfer in network
Provides standardized services such as virtual terminal, file and job transfer and operations
Layer 6:Presentation Layer
Masks the differences of data formats between dissimilar systems
Specifies architecture-independent data transfer format
Encodes and decodes data; Encrypts and decrypts data; Compresses and decompresses data
Layer 5:Session Layer
Manages user sessions and dialogues
Controls establishment and termination of logic links between users
Reports upper layer errors
Layer 4:Transport Layer
Manages end-to-end message delivery in network
Provides reliable and sequential packet delivery through error recovery and flow control mechanisms
Provides connectionless oriented packet delivery
Layer 3:Network Layer
Determines how data are transferred between network devices
Routes packets according to unique network device addresses
Provides flow and congestion control to prevent network resource depletion
Layer 2:Data Link Layer
Defines procedures for operating the communication links
Frames packets
Detects and corrects packets transmit errors
Layer 1:Physical Layer
Defines physical means of sending data over network devices
Interfaces between network medium and devices
Defines optical, electrical and mechanical characteristics
