The long, slow and at times, colorful battle between TCP/IP backers and SNA stalwarts was one of the more acrimonious periods of time in the industry’s history. IBM introduced the concepts and initial components of SNA in 1974 and by the mid-1990s it was locked in a do-or-die battle with IP’s chief proponent – Cisco. 

Cisco and the industry had some fits and starts in promoting TCP/IP and a real SNA alternative, at one point forming the Advanced Peer-to-Peer Internetworking (APPI) group to counter IBM’s SNA advanced technology called APPN (Advanced Peer-to-Peer Networking). While APPI was ineffectual and folded in 1993, it planted seeds that would ultimately sow SNA’s demise.

For its part IBM did just about everything wrong in upgrading older SNA users to APPN -- first it made APPN gear complicated and costly -- it even wanted royalties from potential third parties that could have helped establish the technology. In 1994, an IBM executive promised to "kill" vendors (mostly Cisco) and "eat our own young" before IBM would let any rival cannibalize SNA/mainframe business. 

In addition, IBM threatened lawsuits over the use of some of its technology. While IBM had started losing customers, it still had more than 50,000 SNA installations, so its blustering had some power. But with Cisco licensing Big Blue’s mainframe channel technology in the mid-1990s and the advent of Data Link Switching (DLSw) and tn3270 (which let SNA run over IP networks), the nails were in the coffin. Combine that with the fact that at about that time Gartner said users with SNA as their primary protocol (after about 1995) will spend a total of 20% more than IP users on training staff, hardware and software purchases, and administration. 

You didn’t need a Magic 8-ball to see the outcome. IBM sold most of its young to Cisco in 1999.

Open Systems Interconnect (OSI) technology backers were also making a lot of noise during this period. OSI products and services were based on an international set of standard protocols that were supposed to guarantee interoperability among all vendors and products. IBM and Digital Equipment Corp., in fact, were two of its chief proponents, despite the fact OSI ran completely counterintuitive to SNA and DECnet respectively. The U.S. government throughout the 1980s and 1990s mandated the use of OSI products but changed its tune in 1994 saying TCP/IP could be used instead. The TCP/IP juggernaut moved on and widespread use of OSI products never happened.