SGS-Thomson Microelectronics NV and National Semiconductor Corp have developed a single chip integrated circuit device that enables basic rate Integrated Services Digital Network access between user terminals, such as computers and telephones, and the network administration’s central office switching equipment. Although Thomson and National have worked together on this project, the new U-interface will be marketed separately by the two companies as the ST5410 or TP3410; it will be competing with similar interfaces already developed individually by Siemens, Motorola and AT&T. Unlike the S-interface, which resides on the ISDN terminal end within the proprietry architecture, the U-interface is designed to connect these ISDN islands to other ones via the public network; up until now, reckon Thomson and National, the growth of ISDN has been hindered by a lack of silicon that can interface with the outside world in this way. Intended to be used to provide the basic 2B+1D (two data and one signalling channel) access for private exchanges of fewer than 20 lines with the public network, the ST5410/TP3410 dissipates 300mW of power and uses the 2B1Q line code, in which two binary bits are converted into one quaternary bit for transmission; this is an ANSI and CCITT standard, and is supported by, amongst others, France Telecom; it is also likely to be followed by Japanese suppliers as one of the most commercially viable of the six codes presently put forward. Data can be sent and received at 160Kbps over distances up to three and a half miles with full echo-cancelling, and by acting as a master clock for the timing of the S-interface, it eliminates the need for a second crystal. The ST5410/TP3410 is available now as a 28-pin DIP package in sample quantities, with volume production possible by the year-end, depending on demand; the envisaged cost will be around $50 per device in quantities of 10,000, although this will vary with the various deals secured by the two firms individually; when the ceramic packaging is replaced by a plastic version, this figure will fall to around $20. But when volume demand will arrive is another matter: ISDN has been characterised by more talk than action, and when people speak of it, primary rate access, with 30 B channels, seems the more attractive. However in the UK for example, British Telecommunications, which was incidently responsible for the 2B1Q code that Thomson and National are putting their money on, is due to start up its basic rate ISDN 2 service this April, and with a potential capacity of 90,000 lines, this could give the Thomson-National U-interface the runway it needs to take off.
