OSI Model

Introduction
The Open Systems Interconnection (OSI) model describes Seven Layers that computer systems use to communicate over a network.
The modern Internet is not based on OSI but on the simpler TCP/IP Model. However, the OSI 7-layer model is still widely used, as it helps visualize and communicate how networks operate.

The OSI 7 Layers

• Application Layer
  Implemented in software, the application layer is where users interact. Data is sent from the application layer to the presentation layer.

• Presentation Layer
  The presentation layer converts received data from the application into machine-representable binary format, converting from ASCII to EBCDIC if necessary. It may also involve encryption, compression, and providing abstraction. The SSL protocol is commonly used here.

• Session Layer
  This layer assists in setting up and managing connections. It enables the sending and receiving of data followed by the termination of connected sessions. Authentication and authorization processes often occur here.

• Transport Layer
  The transport layer is responsible for transferring data between systems. It utilizes protocols such as UDP and TCP.
  Within this layer, segmentation occurs. Data received from the session layer is divided into segments. Each segment is assigned a sequence number to aid in reassembling them at the receiving end.

• Network Layer
  The network layer facilitates communication between different computers. It assigns logical addresses, typically IP addresses, to data packets to ensure they reach their correct destinations. Additionally, it handles routing and may involve load balancing.

• Data Link Layer
  This layer deals with the logical transmission of data packets over the physical network. It includes functions such as framing, error detection, and correction.
  Physical addressing is performed in the data link layer. MAC addresses, which are physical addresses, are used for this purpose. MAC addresses of both the sender and receiver are included in the data packet to form a frame.

• Physical Layer
  The physical layer involves hardware components. It is responsible for transmitting raw data bits over the physical medium. Data received from the layers above is converted into signals and transmitted via physical routers to the intended recipients.

Conclusion
In conclusion, understanding the OSI model provides a fundamental framework for comprehending network communication, while the TCP/IP model offers practical solutions to modern networking challenges.