Open System Interconnection (OSI) Model
The OSI model is a conceptual framework for understanding how computer systems communicate. It was developed by the International Organization for Standardization (ISO) in the 1980s and is widely used as a reference model for network design and implementation.
The OSI model consists of seven layers, each of which performs a specific function in the communication process:
1. Physical Layer
- Responsible for the physical transmission of data over a network medium (e.g., cables, fiber optics, wireless).
- Functions include: bit transmission, encoding/decoding, signal modulation/demodulation, and error detection.
2. Data Link Layer
- Establishes and maintains reliable point-to-point connections over the physical layer.
- Functions include: error checking, flow control, media access control (e.g., Ethernet, Wi-Fi), and frame addressing.
3. Network Layer
- Provides routing and network addressing services for data transmission across multiple networks.
- Functions include: IP addressing, routing protocols (e.g., TCP/IP, IPv6), network layer error detection, and traffic routing.
4. Transport Layer
- Provides reliable and sequenced transport of data between end-point applications.
- Functions include: error recovery, flow control, data segmentation/reassembly, and port addressing (e.g., TCP, UDP).
5. Session Layer
- Manages and synchronizes communication sessions between applications.
- Functions include: session establishment/termination, session negotiation (e.g., encryption, compression), and token management.
6. Presentation Layer
- Translates and formats data between different application protocols and the network.
- Functions include: data encryption/decryption, data compression/decompression, and data conversion (e.g., ASCII, Unicode).
7. Application Layer
- Provides user-specific services and applications through the network.
- Functions include: file transfer (e.g., FTP), email (e.g., SMTP), web browsing (e.g., HTTP), and multimedia applications.
Interlayer Communication
Each layer of the OSI model communicates with the adjacent layers using specific protocols. For example:
- Physical layer: Transmission Control Protocol (TCP)
- Data link layer: Ethernet frame
- Network layer: Internet Protocol (IP)
References
- [OSI Model](https://en.wikipedia.org/wiki/OSI_model)
- [ISO/IEC 7498-1:1994](https://www.iso.org/standard/14988.html)
- [Computer Networks: A Top-Down Approach, 8th Edition](https://books.google.com/books?id=z7euBwAAQBAJ&pg=PA27)
- [OSI Model in Detail: 7 Layers Explained](https://www.geeksforgeeks.org/osi-model-in-detail-7-layers-explained/)