This article traces the transition from mainframe SNA connectivity to Ethernet for access to remote mainframe CICS applications and printing services. Our experiences with converting a portion of a mainframe SNA network to Ethernet using IBM’s Communications Server software may be useful to other sites and can help systems programmers and network staff seeking ways to consolidate SNA end-node connectivity with lower-cost solutions.
The State University of New York (SUNY) at Albany’s IBM mainframe computing era began in 1985, when IBM won the contract to replace the Unisys 1100-series machines at Albany and three sister sites. The university’s Unisys 1100/90 system was replaced by an IBM 3083BX that ran VM/SP HPO with MVS/SP running as a preferred guest. Mainframe connectivity to SUNY Central Administration five miles away was accomplished with a T-1 leased line and a refrigerator-size 3725 Communications Front-End Processor (FEP) running NCP/EP.
In 1987, a Periphonics Touch-Tone Voice Response (TTVR) controller was added, allowing student telephone access to grades and course registration. The Periphonics TTVR attached to the FEP, using the SDLC protocol over a V.35 connection, and emulated a remote IBM 3274 control unit. The TTVR controller could handle 36 simultaneous phone connections emulating CICS sessions.
The IBM 3083 was eventually upgraded to a 3084QX and the operating systems were replaced with their XA-architecture counterparts. Most users were utilizing IBM 3270 terminals or PC-based IRMA 3270 emulation cards to connect to MVS/CICS or VM/ CMS over a coaxial network. The university was also installing a thin-wire Ethernet network for connectivity to Sun workstations for academic computing purposes.
Noting the expense of running two separate networks, we replaced most of the SNA coaxial network with Ethernet and installed a (then) revolutionary new product from McGill University called NET3270 that allowed PCs to be used as network gateway servers to the mainframe. These servers connected to the mainframe using coaxial Distributed Function Terminal (DFT) port connections to IBM 3174 communications controllers. Users installed Ethernet cards running the IPX/SPX (NetWare) protocol stack to connect to the NET3270 servers. Adding new NET3270 users was initially cumbersome because many departments were involved in ordering, installing, and configuring PC Ethernet cards. Once completed, however, we gained the benefits of scalability and standardization. Eventually, McGill sold the product to Hummingbird Software, and the product evolved to HostExplorer, a client-based terminal emulation program that uses TCP/IP.
We added direct Ethernet capability to the mainframe in the early ’90s by purchasing a Bus-Tech controller and adding TCP/IP software to VM and MVS. We then migrated all our mainframe users to HostExplorer. Since only registered users were allowed access to CICS systems, we had to track SNA terminal Logical Unit (LU) names and their associated IP addresses in the MVS TCP/IP configuration file. Because our user population was growing and users often changed IP addresses, it was an administrative challenge to keep up with these changes. We instituted a list-serv e-mail list that departmental technical coordinators could send requests to, and moved routine TCP/IP LU to IP mapping configuration changes from the Systems group to an administrative function. Users had to wait until the next day for changes to take effect because the TCP/IP server needed to be restarted during off-hours.
In 1997, we upgraded to a 9672/R21 mainframe running VM/ESA and OS/390 Version 1.2. One of the best things to happen as a result of this upgrade was the installation of a RAMAC disk subsystem with built-in RAID 5 redundancy. Our antiquated 3380 disks were regularly failing. Shortly after this upgrade, we decided to phase out VM/ESA and run OS/390 natively due to the plethora of operating systems the university was supporting,
In 1999, IBM dropped support for the 3725 FEP. We replaced it and the Bus-Tech controller with an IBM 2216 multi-protocol communications controller. This little wonder could handle all our TCP/IP HostExplorer terminal users, our SNA link to SUNY Central, and the Periphonics TTVR controller.
Since many of our users were installing network printers (mostly Hewlett-Packard JetDirects) that spoke TCP/IP, we needed to support CICS and JES printing to these devices. The Network Print Facility (NPF), then an option to the TCP/IP product, fit this need well. NPF acts as a print gateway between the SNA world and the TCP/IP world, allowing CICS users to share departmental LAN printers.