Introduction to Microsoft SNA Server

Although simple one-to-one connections can suffice for many basic computing operations, most organizations require more flexible connectivity between IBM host computers and local area networks (LANs). To meet this need, Microsoft® Systems Network Architecture (SNA) Server exploits client/server architecture to link personal computers to IBM mainframe and midrange computers, such as the IBM AS/400 series, which are accessible using the SNA protocols. The client personal computers can run the Microsoft® Windows NT®, Windows® 95, Windows® version 3.x, or MS-DOS® operating systems, OS/2, or the Apple Macintosh operating system, and can use standard LAN protocols to connect to the server; only the computer running SNA Server must run the SNA protocol. Each personal computer user can have multiple 3270 sessions for concurrent terminal and printer emulation.

The client/server architecture of SNA Server allows the removal of communications processing from client systems so their system resources can be used more efficiently. Client personal computers do not have to run one protocol to access the LAN and another to access the SNA host. Each personal computer can run Microsoft-based networking (named pipes), TCP/IP, IPX/SPX, AppleTalk, or Banyan VINES, within a single-protocol or mixed network, to access SNA Server. SNA Server routes the connection to the appropriate host computer by way of the SNA protocol. The client/server architecture also provides Windows NT, Windows 95, and Windows 3.x applications with the ability to access information on IBM mainframes and midrange computers.

All hardware platforms supported by Windows NT can be integrated with Microsoft SNA Server. SNA Server relies on the built-in security of Windows NT, so administrators can manage a single set of user accounts. SNA Server is also fully integrated with Windows NT system monitoring and management services, and provides automatic server and connection fault tolerance. Microsoft Windows SNA Server has a complete 32-bit, multithreaded architecture designed for maximum performance, scalability, and reliability. Also, SNA Server is fully compliant with the Microsoft Windows Open Services Architecture (WOSA), providing a consistent interface to organization computing environments and hiding the complexities of connectivity from applications.

Microsoft SNA Server provides support for the following APIs for distributed SNA applications:

• Advanced Program-to-Program Communications (APPC) for applications that communicate peer-to-peer with other APPC applications using the logical unit (LU) type 6.2 protocol.
• Common Programming Interface for Communications (CPI-C) for applications that communicate peer-to-peer with IBM Systems Application Architecture (SAA) applications using the LU type 6.2 protocol.
• Logical Unit Application (LUA) programming interfaces for applications (using LUA/Request Unit Interface or LUA/Session Level Interface APIs) that need direct access to LU types 0, 1, 2, and 3 data streams.

With the Microsoft SNA Server Software Development Kit (SDK) you can design applications that use SNA Server APIs, such as APPC or CPI-C, or the 3270 emulation client. The following sections present an overview of the SNA Server SDK and clarify the significant APIs and development issues for you to create effective SNA Server applications.