SNA

Systems Network Architecture (System Network Architecture) - a general description of the structure, formats, protocols used to transfer information between IBM programs and equipment, developed by IBM in 1974 , was created to integrate into IBM mainframe global networks.

SNA is a seven-level stack of network protocols that is close but not consistent with the OSI network model :

• Physical Control - provides the generation and coding of electrical signals, the operation of physical interfaces, network topology and communication medium (eg cable)
• Data link control (DLC) —includes several link layer protocols, including Synchronous Data Link Control ( SDLC , Synchronous Data Link Control Protocol) for hierarchical networks and Token Ring for peer-to-peer local networks, OSI compliant link level. (however, it does not cover the full functionality of Data Link layer OSI);
• Path control - provides addressing, routing and fragmentation / defragmentation of data packets, covering part of the functions of the channel and network layers of OSI;
• Transmission control - provides connection management, including data encryption / decryption, providing functionality included in the OSI network and transport layer;
• Data flow control - a level of data flow control , including connection establishment, data transmission order, transmission suspension on demand, and group exchange. Includes OSI transport and session level functions;
• Presentation services - management of data conversion in various formats, resource sharing and transaction synchronization. Includes part of the session-level, presentation and OSI application functions;
• Transaction services is a level of distributed data processing and control management applications.