The integration of LAN-based networks using protocols such as IPX/SPX or TCP/IP with SNA-based host systems such as IBM mainframes and AS/400 systems.
Systems Network Architecture (SNA) networks originally developed separately from local area networks (LANs). As a result, both types of network have their own PC adapters, cabling, and protocols. LANs are built primarily around Ethernet using NetBEUI, IPX/SPX, or TCP/IP protocols, and they are connected into wide area networks (WANs) using routers and bridges. LANs and WANs support only non-SNA protocols.
As a result, many large companies have developed a two-tier network, consisting of a traditional LAN-based Ethernet network and an entirely separate SNA host-based network. However, because of the cost of maintaining separate networks, many have merged their SNA-only networks with non-SNA networks.
Early attempts at LAN-host integration involved directly connecting PC computers to IBM host systems using SNA hardware adapters and SNA protocols across a dedicated SNA network. Each PC was connected to a local IBM control unit such as an IBM 3174 or IBM 5294 using coaxial or twinax cabling. Standards were developed to allow SNA and non-SNA protocols to share the same network, but networking engineers soon found that mixing SNA and TCP/IP was like mixing oil and water, especially with regard to WAN connections, in which Data Link Control (DLC) timeouts and other difficulties made network management complex.
One solution is to install a TCP/IP protocol stack directly on the mainframe host, but this often results in degradation of host performance and additional challenges in terms of IP address administration.
Another solution is the LAN-to-SNA gateway. The gateway computer lets desktop PCs access applications and data on the mainframe host using traditional LAN protocols. TCP/IP is used to connect the desktop PC and the SNA gateway, while SNA is used to connect the SNA gateway and the mainframe host. This LAN-to-SNA gateway solution has become the de facto standard for providing host access to LAN-based PCs. An example of an SNA gateway application is Microsoft SNA Server, which provides LAN-to-SNA gateway services over a variety of network protocols that include NetBEUI, TCP/IP, IPX/SPX, Banyan VINES, and AppleTalk.