LU2 Connectivity with Host Integration Server


For all you youngsters out there, maybe you wouldn't know a logical unit if it hit you over the head. But for many enterprises, LU2 is a key protocol they use to integrate with mainframe or legacy systems.

Maybe You Need a Refresher Course?

LU2 supports communications between terminals and screen-oriented mainframe applications, often running under IBM's CICS. (For more on SNA and LU types, see IBM's redbook from 1995) Many (most?) older CICS apps used an architecture that did not foresee the need to interconnect applications broadly - they exposed only a single interface, the terminal-based user interface. In some cases the UI logic, the 3270 screen formatting, is so tightly wound up in business logic, or even workflow or screen flow (something like the "page flow" concept in web apps today), that it is, practically speaking, impossible to uncouple the UI from the logic.

Laws of the Land

These days we have MVC patterns and multi-tiered architectures, but older designs didn't have the benefit of hindsight that we do. They also didn't have the same engineering constraints - Twenty years ago, there was no "world wide web". The economics of computer processing power were governed by Grosch's Law, named after Herb Grosch, who held that compute power increases in proportion to the square root of compute cost. This meant, bigger computers were more economical. At the same time, the cost of compute power was the factor to optimize for - as opposed to the cost or speed of application development, for example. People were cheap compared to the equipment. These engineering and economic forces encouraged the designers of older systems to invest in monolithic, powerful centralized nodes of computing - a mainframe surrounded by dumb terminals. Call it the Big System design model. LU2 is how terminals talked to those Big Systems.

Grosch's Law eventually succumbed to Moore's Law, which predicted that the density of transistors on a chip would double every 18 months. The relevant corollary is that compute power would get cheaper and cheaper, as density increased. This was not quite the antithesis of Grosch's Law, but it inverted the value relationship between people and equipment, so much so that Grosch's law did not "become incorrect" as some have said, but rather it became irrelevant. A key implication of the compounding effect of Moore's Law has been that, in any information system, the cost to optimize for is no longer the equipment, but the people. A mid-sized computer no longer costs half a million 1976 dollars. Instead you can go to and get it shipped next day, for under $1000. But IT people haven't gotten much cheaper!

This inversion changed everything, including the idea that monolithic systems were optimal. Thanks to the persistent phenomenon that Gordon Moore described, we now design under a distributed, composable model (eg, our current model of SOA and "web services), and we (mostly) optimize not for the cost of the equipment, but for the cost of the people that run, program, and use the equipment.

Big Systems Are Still Here!

So that explains why Big Systems were so popular, why they were hard to connect to, and why we have sort of been gradually migrating away from the Big System model, in macro terms. But Big Systems are still here, still in place, working. The changes in compute economics haven't eliminated the need to interoperate with legacy systems. And the rules are set - if you want to talk, ya gotta go through a terminal protocol. So today, LU2 is often used for application-to-application communication, where the calling application impersonates a terminal. Screen scraping.

HIS 2006 will add LU2 Connectivity

In the next release of Microsoft's Host Integration Server (HIS 2006), Microsoft plans to include a new feature called "Session Integrator". Session Integrator is similar to HIS's current Transaction Integrator feature, but it will work with LU0 and LU2 connections (whereas TI works with LU6.2 and TCP/IP). This was first disclosed by the HIS team at the IT Forum 2005 event in Barcelona, in November 2005.

Session Integrator will be included in HIS 2006 Enterprise Edition, which will ship as part of BizTalk 2006. If you buy BizTalk 2006 (any edition) you get a copy of HIS 2006 included. HIS 2006 will go into public beta Real Soon Now. The public general release of this product is planned for later this year.

Even though web services are all the rage, and even though IBM is implicitly discouraging SNA deployments by publishing end-of-service dates for SNA-based network gear and software, and by improving the TCP/IP connectivity of Mainframe systems... despite all that...there are still many companies out there who need SNA-based communications solutions in the near term. That's what this new feature in HIS 2006 is designed to support.

Yes, Microsoft will still invest most strongly in webservices efforts, but we also need to satisfy the practical requirements of customers. Nobody can afford to start all over again. Every company or organization has some existing "investments" or systems in place, and not all of them support web services. We need to do what we can to make interop with those existing systems, possible and easy. Host Integration Server is a big part of Microsoft's answer to that requirement.

hasta luego,