The OSI Model - jude-lindale/Wiki GitHub Wiki
- the Open Systems Interconnection or OSI reference model, developed by the International Organisation for Standardization, was created to enable different types of networks to be linked together
| Layer | Function | Examples |
|---|---|---|
| 7. Application | Interacts with application programs that incorporate a communication component such as your Internet browser and email. This layer is responsible for logging the message in, interpreting the request, and determining what information is needed to support it. | HTTP, FTP, SMTP (email) |
| 6. Presentation | Accepts and structures the messages for the application. It translates the message from one code to another, if necessary. This layer is responsible for data compression and encryption. | ASCII, JPEG |
| 5. Session | Provides the control functions necessary to establish, manage, and terminate the connections required to satisfy the user request. | NFS, SQL |
| 4. Transport | Is concerned with message integrity between source and destination. It also segments/reassembles (the packets) and handles flow control. | TCP, UDP |
| 3. Network | Accepts outgoing messages and combines messages or segments into packets, adding a header that includes routing information. It acts as the network controller. | IP, IPX |
| 2. Data link | Handles error recovery, flow control (synchronization), and sequencing (which terminals are sending and which are receiving). It is considered the “media access control layer” and is where media access control (MAC) addressing is defined | MAC addresses |
| 1. Physical | Provides the electrical and mechanical connection to the network | NICs, twisted-pair cable, fiber |
Note
Network administrators often describe networking problems by layer number. For example, a physical link problem is described as a layer 1 problem; a router problem is a layer 3 issue; and so on