The OSI model defines a seven-layer architecture for a complete communication system:
1. Application Layer
- The application layer is the topmost layer of the OSI model. Data transmissions frequently originate in the application layer of the origin device and terminate in the application layer of the target device.
- This layer deals with the identification of services and communication partners, user authentication, and data syntax.
- Some common application layer protocols include hypertext transfer protocol (HTTP), Telnet, and file transfer protocol (FTP).
2. Presentation Layer
- The presentation layer is a software layer that formats and encrypts data that will be sent across a network, ensuring compatibility between the transmitting device and the receiving device.
- The presentation layer includes protocols such as ASCII, JPEG, and MPEG.
3. Session Layer
- For data transfer to occur between applications on separate devices, a session must be created.
- The purpose of the session layer is to manage, synchronize, and terminate connectivity between applications, ensuring coordinated data exchange while minimizing packet loss.
- The session layer can provide for full-duplex, half-duplex, or simplex communications.
4. Transport Layer
- In the OSI model, the transport layer receives messages from the data layer and converts them into smaller units that can be efficiently handled by the network layer.
- The Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are popular transport layer protocols for devices that connect to the internet.
5. Network Layer
- The network layer provides the features and functions that transfer data sequences from the host device to a destination device. Network layer devices use protocols such as IP, ICMP, and IPX.
6. Data Link Layer
- Data packets are encoded and decoded into bits in the data link layer, which may be divided into two sub-layers: media access control (MAC) and logical link control (LLC).
- Hardware network interface controllers are typically assigned a MAC address by the manufacturer that acts as a unique device identifier and network address within a network segment.
7. Physical Layer
- The physical layer defines the electrical and physical requirements for networked devices with control over the transmission and reception of unstructured raw data over the network.