OSI
A reference model developed by the ISO to serve as a foundation for networking architecture and standards for worldwide communications. The model defines a 7-layered, hierarchical framework of functionality and peer-to-peer protocols. The seven layers are named: Layer 7 Application Layer Layer 6 Presentation Layer Layer 5 Session Layer Layer 4 Transport Layer Layer 3 Network Layer Layer 2 Data Link Layer Layer 1 Physical Layer See definitions of respective names for a layer's functional content.
More: Open System Interconnection