This month sees Unisys Corp shipping its new Communications Access Processor which enables Unix servers to plug into SNA networks built around IBM mainframes. As reported earlier this year (CI No 1,974), the system provides hardware, communications and the interface software, and it is based on the previous generation DCP family of communications processors for the 2200 mainframes, which started life as an Am2901 bit-slice emulation of a very venerable Univac minicomputer, although gate arrays are presumably used these days. The system is said to be transparent in that it enables the Unix system to appear to the SNA network as another mainframe. Initially, the processor will be available in two models: the CAP 200 which supports up to 30 communication lines and the CAP 250, which supports 180 lines. Unisys says that by using custom-built processors, the system supports all communication functions, SNA sessions and other functions on 4Mb of memory. At present, CAP has to be used in conjunction with Unisys U6000 Unix servers. These systems handle data stream conversion from 3270 terminal block mode to the character mode applications in Unix. While the service processors are the U6000 systems, the systems handling the actual application load are not vendor-specific.
3270-to-Unix, Unix-to-370 access
The processor enables any 3270 terminal in an SNA network to access Unix applications while the Unix workstations can access the mainframe’s database. Unlike bridges, routers and gateways, the processor operates at Physical Unit 4 and 5 levels and doesn’t ned to rewrite or re-engineer code and applications. This enables both Unix and SNA communication protocols to operate across the SNA backbone and the network can manage user sessions independently of the host. Also, one major benefit to users looking to downsize is that the mainframe need not be central to every transaction, but the benefits of SNA are still available. Linking the two disparate worlds of Unix and SNA Unix uses character terminals rather than block mode, is network- rather than host-based and can’t be accessed by IBM’s NetView network management tools – can be achieved in a number of ways. One is by replacing terminals with personal computers loaded with both local network and communications boards to bridge the two environments. That’s expensive and complex, says Unisys. A second alternative is to use a standard Unix box as the front-end processor, which can be slow, given that it is a general purpose box rather than a communications controller. The third is to use a Unix gateway, which can actually add to the processing load on the mainframe rather than offloading it. Enter Unisys with what it claims is the perfect, and currently unique system. Unisys sees the processor as way of migrating users from mainframes to a more open environment, although its primary role at present is the integration of Unix. The 200 CAP costs UKP42,000 and CAP 250 is UKP56,000. A dedicated server is also required at the Unix end, and will cost another UKP10,000, and there is a further UKP10,000 implementation services charge. Unisys says it is considering making the software available to non-Unisys servers. According to Electronic News, IBM’s Advanced Peer-to-Peer Networking – an attempt to open up SNA, but still relatively immature – has shaken users’ perception that SNA is rock-solid, and this has created an opportunity for Unisys. Likewise, AT&T Co’s NCR Corp, which has been shipping products supporting both SNA and TCP/IP from its NCR Comten unit, may face stiff competion from Unisys in an emerging market that could prove to be lucrative. Unisys claims it has had rave reviews for the thing, and the first customer for is Boatmen’s Bancshares Inc, a St Louis-based financial services company, using a Unisys U6000 server for a credit scoring application, with access from the company’s existing 1,000-plus 3270 terminals.
