Description of the 7 OSI layers.

osi.md

OSI Layers

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstraction layers. Each layer in the OSI model serves a specific purpose and communicates with the adjacent layers. Here's a brief description of each layer from the bottom (Layer 1) to the top (Layer 7):

Physical Layer (L1):

• Function: Deals with the physical connection between devices.
• Activities: Transmission and reception of raw bit streams over a physical medium, such as cables or wireless signals.
• Devices: Hubs, cables, repeaters.

Data Link Layer(L2):

• Function: Provides error detection and correction within the physical layer.
• Activities: Frame synchronization, error checking, and flow control.
• Devices: Switches, bridges, network interface cards (NICs).

Network Layer (Layer 3):

• Function: Responsible for logical addressing, routing, and forwarding of data packets between different networks.
• Activities: IP addressing, routing, packet forwarding.
• Devices: Routers, Layer 3 switches.

Transport Layer (Layer 4):

• Function: Manages end-to-end communication, ensuring data integrity and reliability.
• Activities: Segmentation, flow control, error recovery.
• Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).

Session Layer (Layer 5):

• Function: Establishes, manages, and terminates communication sessions between applications.
• Activities: Dialog control, synchronization, session management.
• Example: NetBIOS, RPC (Remote Procedure Call).

Presentation Layer (Layer 6):

• Function: Translates data between the application layer and the lower layers, ensuring that data is in a readable format.
• Activities: Data encryption, compression, and translation.
• Formats: ASCII, JPEG, GIF.

Application Layer (Layer 7):

• Function: Provides network services directly to end-users or applications.
• Activities: Network-aware applications, user interfaces.
• Protocols: HTTP, FTP, SMTP.

The OSI model serves as a reference for understanding and designing network architectures, but in practice, the TCP/IP model is more commonly used, which combines the OSI model's top three layers into a single application layer.