Operating Systems

Deploying SNA in IP-Based Environments

4 Pages

Systems Network Architecture (SNA) over IP solutions have evolved over the last 15 years to provide a variety of options. The optimal solution depends on the application environment and the evolution of legacy equipment in those environments. Typically, users modernize their networks, then deploy technology that lets them transport the SNA application traffic over the new IP network.

This article describes the evolution of SNA networks in IP-based environments, the modernization use case, and the tools needed to migrate from legacy SNA network structures to IP-based solutions. This migration involves replacing traditional 3270 terminals with emulation programs (TN3270) for SNA Logical Unit (LU) Type 2 applications and providing transport emulation (Enterprise Extender) that replaces SNA infrastructure components to support SNA Advanced Peer-to-Peer Networking (APPN) applications (LU Type 6.2) and specialty devices (LU Type 0). The resulting solution leverages the advanced functionality and reliability of modern networking hardware with these proven IBM software solutions for a simplified, effective SNA over IP solution.


Since the inception of the IBM mainframe, a key characteristic has always been investment protection, particularly for application software. Many current System z customers have considerable investments in SNA-based applications. Modernizing SNA reduces the costs of maintaining and operating what may be an aging SNA infrastructure while preserving the investment in those applications.

The modernization of corporate network infrastructures has shifted in the last decade from SNA networks and applications to TCP/IP and Internet technologies. Often, applications have changed and processes have been re-engineered to use TCP/IP rather than SNA.

The ultimate goal of SNA modernization is preserving and enhancing SNA applications on the System z and in the branch environment for as long as the SNA applications remain a valuable asset. Simultaneously, wide area SNA application-level traffic will be transported over an IP Wide Area Network (WAN), and SNA network-level traffic will be consolidated to the data center, or even to the System z itself.

Today, organizations still have a heavy investment in SNA-based transaction programs and applications on their mainframes. According to IBM, as of 2009, more than $20 trillion has been invested in SNA-based applications in more than 40,000 organizations worldwide on the mainframe and other server platforms. More than 1 trillion lines of customer-written application code is mainframe-based CICS, DB2, and IMS. IBM surveys indicate that SNA-based applications account for 61 percent of WAN traffic and 66 percent of WAN budgets. Refer to the accompanying sidebar, “SNA’s Evolution,” for further background about why and how IBM developed SNA, contributing to the capabilities of the modern IBM System z mainframe, which is today the dominant Online Transaction Processing (OLTP) server platform.

SNA Remains Essential

There are five primary factors contributing to the continued use of SNA-based applications:

  1. SNA is stable, trusted, and relied on for mission-critical business applications worldwide.
  2. Seventy percent of the world’s corporate data is still handled on the mainframe and much of it is used by SNA applications.
  3. SNA is connection-oriented with many timers and control mechanisms that ensure reliable delivery of data.
  4. Rewriting stable, well-tuned business applications to change from SNA program interfaces to TCP/IP sockets can be costly and time-consuming.
  5. Many businesses are using Web-enabling technologies to make the vast amount of centralized data available to the TCP/IP-based Web environment while maintaining SNA Application Program Interfaces (APIs).

As a networking protocol, SNA is rapidly approaching its end of life, but SNA applications, and the SNA APIs to which they’re written, remain viable and important. IP technology is well-suited for reliable, high-speed communications lines; it’s ubiquitous and steadily improving through contributions from the open source community.

4 Pages