OSI/ISO Reference Model of Networking

The Open Source Interconnection (OSI) model defines a networking framework to implement protocols in seven layers. Use this handy guide to compare the different layers of the OSI model and understand how they interact with each other.
Open System Interconnection (OSI) Reference Model was developed by the International Standards Organization (ISO) to provide a framework for understanding how information is sent from one computer to another. It describes seven layers, with each layer intended to provide a well-defined order to ensure data has been successfully transmitted between devices.

1. Physical (Layer 1)

OSI Model, Layer 1 conveys the bitstream -electrical impulse, light, or radio signal – through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards, and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

2. Data Link (Layer 2)

At OSI model, layer 2, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management. The data link layer is divided into two sub-layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub-layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control, and error checking.

3. Network (Layer 3)

Layer 3 provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control, and packet sequencing.

4. Transport (Layer 4)

OSI Model, Layer 4, provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

5. Session (Layer 5)

This layer establishes, manages, and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the application at each end. It deals with session and connection coordination.

6. Presentation (Layer 6)

This layer is independent of differences in data representation (eg, encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

7. Application (Layer 7)

OSI Model, Layer 7, supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely at the application level. Tiered application architectures are part of this layer.
7 layers of OSI/ISO Refrence Model of Networking

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