Open Systems Interconnection (OSI) is an acronym for Open Systems Interconnection. It was created in 1984 by ISO or the International Organization for Standardization. It is a seven-layer ARCHITECTURE, with each layer performing distinct functions. These seven layers work together to send data from one person to another across the globe.

• Physical Layer: The physical layer is the lowest layer in the OSI reference model. It is in charge of establishing a physical connection between the devices. Bits of information are stored in the physical layer. It is in charge of sending individual bits from one node to another. When this layer receives data, it converts the signal received into 0s and 1s and sends them to the Data Link layer, which reassembles the frame.
• Data Link Layer: The data link layer is in charge of message transport from node to node. The major purpose of this layer is to ensure that data transfers from one node to another through the physical layer are error-free. There are two sublayers in the Data Link Layer:
  • Media Access Control (MAC)
  • Logical Link Control (LLC)
• Network Layer: The network layer is responsible for data transmission between hosts that are CONNECTED to various networks. It also handles packet routing, which is the choosing of the shortest path to send a packet from a large number of options. The network layer places the IP addresses of the sender and receiver in the header.
• Transport Layer: The application layer receives services from the transport layer, while the network layer receives services from the transport layer. Segments are the units of data in the transport layer. It is in charge of the full message's delivery from beginning to end. If an error is detected, the transport layer ACKNOWLEDGES the successful data transmission and re-transmits the data.
• Session Layer: This layer is in charge of establishing connections, maintaining sessions, authenticating users, and ensuring security.
• Presentation Layer: The data from the application layer is retrieved and processed here so that it may be transmitted across the network in the proper format.
• Application Layer: The Application layer, which is implemented by network applications, is at the very top of the OSI Reference Model stack of layers. These PROGRAMS generate the data that must be sent across the network. This layer also acts as a window for application services to connect to the network and show the information they receive to the user.