The OSI model provides a way of describing how data is transmitted over a network. The model addresses software, hardware and data transmission. The OSI model was created by the ISO as a way to address the problem of incompatibility amongst proprietary networking systems that were developed, controlled and owned privately.
The OSI model is made up of 7 layers and they are labeled in descending order and you can see in the image. Each layer of the OSI model has a specific function and associated software or devices. In this tutorial I am going to give you the functions of the 7 layers of the OSI model.
Layer 1: Physical Layer
The function of the physical layer is to define mechanical, electrical, procedural, and functional specifications for activating, maintaining and deactivating the physical link for bit transmission between end devices on a network. The functional specifications of the physical layer define characteristic such as physical data rates, maximum distance over which data can be transmitted, voltage levels, etc
Layer 2: Data Link Layer
The data link provides the definition of how data must be formatted for transmission. The data link layer also defines how access to the physical media is controlled. Error detection and error correction which ensure reliable delivery of data is also performed at the data link layer.
Layer 3: Network Layer
The network layer connectivity and path selection between two hosts on the same network or separated networks.
Layer 4: Transport Layer
The transport layer defines services that segment, transfer and reassemble the data for particular communications between hosts. The transport layer abstracts transport implementation from the upper layers. Further more the transport layer establishes, maintains and terminates virtual circuits.
Layer 5: Session Layer
The functions of the session layer is to establish, manage and terminate sessions between communicating hosts. The session layer also synchronizes dialog between the presentation layer of the two communicating hosts and manages their data exchange. The session layer offers provisions for efficient data transfer, class of service and exception reporting of session layer, presentation layer (layer 6) and application layer (layer 7).
Layer 6: Presentation Layer
The function of the presentation layer is to ensure that the information which is sent to the application layer is readable by the application layer the other end system it is communicating with.
Layer 7: Application Layer
The application layer is the one the user interacts with. This layer provides services to the applications of the user e.g. file transfer, emails, etc. The application layer establishes the availability of intended communication partners and synchronizes and establishes agreement on procedures for error recovery and control of data integrity.
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