OSI : Open Systems Interconnection. Essentially, this a conceptual model for specifying data communications networks in a structured & organised way. The seven layers, and their functions, are:

1. Physical layer – electrical details; cables, connectors, voltages

2. Data link layer – procedures for data transfer, including error handling

3. Network layer – routing of data

4. Transport layer – controls flow of data between users

5. Session layer - establishes, manages & terminates connections

6. Presentation layer – syntax & semantics mapping

7. Application layer – interface to application