OSI LAYERS Part 1 || Networking || CCNA

Описание: The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven distinct layers. It was developed by the International Organization for Standardization (ISO) to promote interoperability between different vendors' networking technologies. Each layer in the OSI model performs specific tasks and communicates with the layers above and below it. The layers are as follows:

1. *Physical Layer (Layer 1):*
This is the lowest layer, responsible for transmitting raw bits over a physical medium, such as cables or wireless signals.
It deals with hardware components like cables, switches, and network interfaces.
It defines characteristics such as voltage levels, data rates, and physical connectors.

2. *Data Link Layer (Layer 2):*
The data link layer manages the reliable transmission of data frames between devices directly connected on the same network.
It provides error detection and correction, as well as flow control.
Ethernet, Wi-Fi, and PPP (Point-to-Point Protocol) are examples of data link layer protocols.

3. *Network Layer (Layer 3):*
The network layer is responsible for routing packets between different networks.
It uses logical addresses (e.g., IP addresses) to determine the best path for data to travel from the source to the destination.
IP (Internet Protocol) is a crucial protocol of the network layer.

4. *Transport Layer (Layer 4):*
The transport layer ensures reliable data delivery between applications running on different devices.
It manages end-to-end communication and handles segmentation, reassembly, and error recovery.
TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are examples of transport layer protocols.

5. *Session Layer (Layer 5):*
The session layer establishes, manages, and terminates communication sessions between applications.
It enables synchronization and checkpointing of data exchange between systems.
This layer is not as widely used in modern network architectures, and its functions are often integrated into the transport layer or application layer.

6. *Presentation Layer (Layer 6):*
The presentation layer is responsible for data format translation, encryption, and compression.
It ensures that data from the application layer of one system can be understood by the application layer of another system.
This layer deals with data representation and syntax, enabling compatibility between different data formats.

7. *Application Layer (Layer 7):*
The application layer is the topmost layer and is the one closest to end-users.
It provides network services directly to user applications, enabling functions like file transfer, email, and web browsing.
Application layer protocols include HTTP, FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol), and others.

The OSI model serves as a reference model for understanding network communication and is widely used for educational purposes, but in practice, modern networks often implement a more simplified version known as the TCP/IP model, which combines some of the OSI layers for greater efficiency.

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