Blackheath, London-based Brown’s Operating System Services has released version 3.1 of its DN3270 emulation software which, together with a Brown’s Box at the other end enables remote personal computer users to communicate asynchronously with IBM mainframes. The asynchronous link is significant, says Brown’s, because it means that the PS/2 range as well as any MS-DOS personal computer, most of which have built in asynchronous links, can be used for distributed computing, therefore reducing costs. The company also disputes claims (mostly from IBM) that an asynchronous link is not as desirable as a synchronous one, arguing that in block mode transmission, for which Brown’s provide a special protocol, the transmission rates are comparable. It also points out that the asynchronous connection has the added advantage of supporting cellular networks, albeit at their reduced data transmission rates.
Brown’s Box
The system is in direct competition to other micro-to-mainframe links, including IBM’s 3745 and other third party networks, British Telecom’s SPAD, which is part of its Packet SwitchStream service and the IBM SDLC dial-up network. The DN3270 provides IBM 3278 terminal emulation on the remote machine via the asynchronous port. It can provide connection over X25 networks, the public switched telephone network, and cellular nets. The data is transmitted in Brown’s proprietary Block Mode Protocol, enabling the personal computer locally to emulate the IBM 3270 screen display and editing functions – so data can be entered onto the display and edited without anything being transmitted to the mainframe. This is to avoid the traditional asynchronous character by character approach which means that each character must be sent over the network and echoed back – expensive on data network charges. At the host end, a Brown’s Box is installed which appears to the mainframe’s front end processor as a 3274-style cluster controller. The box is a protocol converter when used with the DN3270, converts Brown’s Block Mode Protocol into a synchronous signal acceptable to the mainframe. Brown’s reckons that all this manipulation of the data results in lower costs for the user. Brown’s reckons that the cost averages out at around UKP300 per personal computer, for 100 installations. Prices do depend though on the user’s frequency of use. A 12-port Brown’s box costs UKP13,500. How many users it will support depends on how often they want to use it, numbers can vary from 50 to over 100. Obviously, the more users it supports, the less the cost per user. The system is therefore aimed at large numbers of users, including agents and customers, as well as employees at home. Brown’s reckons that the most cost-effective approach is to have around 100 personal computers connected to the network. DN3270 Version 3.1 now supports up to seven sessions, with one printer session. It requires 128Kb of memory. Release 3.1 also includes a 5250 model for 5250 emulation for connection to System 36, 38 and AS/400s. A Viewdata model emulates Prestel viewdata and the View5250 combines all the models.
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