The OSI model
Definition
The Open Systems Interconnection model (OSI model) is a conceptual model that characterises and standardises the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology
| Number | Name | Protocol data unit (PDU |
|---|---|---|
| 7 | Application Layer | Data |
| 6 | Presentation Layer | Data |
| 5 | Session Layer | Data |
| 4 | Transport Layer | Segment, Datagram |
| 3 | Network Layer | Packet |
| 2 | Data Link Layer | Frame |
| 1 | Physical Layer | Symbol |
Abstract Layers
- Layer 1: Physical Layer
- unstructured raw data between a device and a physical transmission medium
- converts the digital bits into electrical, radio, or optical signals
- Layer 2: Data Link Layer
- provides node-to-node data transfer
- detects and possibly corrects errors that may occur in the physical layer
- defines the protocol to establish and terminate a connection between 2 physically connected devices
- defines the protocol for flow control between them
- Layer 3: Network Layer
- provides the functional and procedural means of transferring variable length data sequences (called packets) from one node to another connected in “different networks”
- Layer 4: Transport Layer
- provides the functional and procedural means of transferring variable-length data sequences from a source to a destination host, while maintaining the quality of service functions.
- Layer 5: Session Layer
- controls the dialogues (connections) between computers
- establishes, manages and terminates the connections between the local and remote application
- Layer 6: Presentation Layer
- establishes context between application-layer entities, in which the application-layer entities may use different syntax and semantics if the presentation service provides a mapping between them
- Layer 7: Application Layer
- layer closest to the end user
- interacts with software applications that implement a communicating component