Dataflex Design Ltd, based in South Wimbledon, London in the UK, looks set to give ISDN world what it has been waiting for – a cheap and cheerful basic rate adaptor for MS-DOS micros that can be plugged into the serial port and use standard communications software. Dataflex is best known for its pocket modems and is following the same pattern with its UKP600 ISDN V24 Adaptor which is currently undergoing British Approvals Board for Telecommunications trials and which the company hopes to launch in late September. The main shortcoming of the product is that it cannot use ISDN’s full 64Kbps, a limitation imposed by the computer’s serial port and one that is shared by all products that connect to the machine in this fashion. Instead the adaptor uses the V110 standard method of rate adaptation to provide speeds of 2,400bps, 4,800bps, and 19,200bps. Unfortunately, to achieve the device’s top speed of 38.4Kbps the company has had to use proprietary rate adaptation, which means that to get the most out of it there needs to be another Dataflex device at the far end. The figure of 38.4Kbps also assumes that the communicating micros can drive their serial ports fast enough. Presumably, if MNP 5 or V42bis compression is incorporated into the communications software even higher effective throughputs are possible. Dataflex has attempted to make its ISDN adaptor compatible with existing communications software by making it respond to the standard Hayes AT command set. The extra parameters that ISDN demands, such as specifying which ISDN B channel should be used for data calls can be controlled by setting the adaptors extra ‘s’ registers. Marketing manager Dave Mendes said that the product is designed as a simple introduction to ISDN for many of our modem customers. He added that the next step would be to produce an adaptor that fits internally into the AT bus, thus enabling speeds approaching the full 64Kbps. However such a device requires specialised communications software to run it.
