A recent study carried out by Ovum Ltd splits up ISDN components parts into three categories – those for an ISDN telephone or NT1; those for an asynchronous terminal adaptor; and those for an ISDN PABX extension line card. There is a great deal of overlap between these various areas, with S interfaces being required by each, for instance, and both the first and last categories needing Layer 2 and 3 support – either in the form of a dedicated chip or implemented in software on a general purpose microprocessor. The HPC16400 communications controller from the National Semiconductor Corp-SGS-Thomson SA partnership contains two full-duplex HDLC channels, with the Layer 2 and 3 functions implemented through the software. One example of the NatSemi theory of keeping the Layer 1 and 2 support separate is demonstrated by the use of this device with the S interface device for a terminal. In this case, the controller would handle Layer 2 and 3 functionality, with the Combo product added to deal with the voice filtering and codec coder-decoder functions.

Cross-over According to the Ovum report, the ways the various suppliers deal with this cross-over in requirements falls into two main categories. Intel Corp and NatSemi, for instance, have each adopted the approach of developing a small range of circuits with limited functionality but with wide applicability, to achieve volume sales as early as possible, with more specific functions being implemented in software. Advanced Micro Devices Corp and Siemens AG on the other hand, have developed a much wider range of chips, each with a specific function – for instance, they have designed separate S interface chips for use in a terminal and in a PABX line card. The report reckons that at the moment – and probably up until the early 1990s – most of the chips will provide Layer 1 and partial Layer 2 functionality only, with suppliers providing their own software to support up to Layer 3 like AMD’s AmLink and Intel’s ISP 188. The latter was developed by a US software company, DGM & S to run on

Intel’s 80188 and all the iAPX86 processors along with its S interface product and voice Combo. NatSemi’s current software offering, the ISDN Basic Rate Interface package is implemented on the HPC 164000, including drivers for both Layer 1 and Layer 2 that control the resources of the chips.

For the future, suppliers will be able to implement ISDN functionality through to Layer 3, with U interface chips becoming more widely available in around three or four years’ time. For although most of the manufacturers do have a U interface product already, they are non-standard, proprietary offerings. AT&T Co recently joined the other suppliers and announced plans to manufacture a 2BIQ U-interface chip set, which the phone company claims is its first design which has as its objective full compliance with the range of ANSI U-interface standards.

Moving on to post-1992, the Ovum study expects to see the first ISDN application chips, providing Layer 1 to 7 support for common ISDN applications, like Group IV facsimile. Shor.pl 71 ter term – over the next 12 months – NatSemi, for instance, is developing an alternative architecture version of its S interface circuits, which will incorporate the GCI General Communications Interface bus as well as the Digital Signal Interface and MicroWire buses. The GCI is a chip-to-chip interface developed back in 1984 by CGE-Alcatel SA, Italtel SpA, Plessey Co Plc and Siemens – the so-called Gang of Four. It emerged as a superset of Siemens own ISDN-Oriented Modular – an acronym which definitely loses something in the translation from the German or then again, perhaps not. Siemens now has its own version IOM-2, which covers the ISDN aspect, but unlike GCI does not encompass analogue line cards.

Cost reduction Advanced Micro’s European Strategic Marketing Manager, Charles Louisson, claims that AMD will have converted all its products to be compatible with IOM-2 by the middle of next year. Another focus is cost reduction. Said Louisson, In most cases this means greater integr

ation, particularly for ISDN terminals. If an analogue phone costs just $10, then the cost of the silicon in an ISDN phone has to be brought down to make it competitive. At the moment, though, there’s an awful long way to go. The Ovum study gives a 1989 total cost for an ISDN telephone of $80 – $400 to the end user – comprising $40 for the chips and $40 for the other equipment such as display, case, microphone and keypad. By 1995, those figures have been reduced to $10 for the chips and $25 for the other elements, amounting to a total cost of $35 around $80 end user price. And the prices are falling fast Ovum’s 1989 S interface price of $25 is half the cost the research outfit quoted in its 1986 report. The falling cost of ISDN chips will be the key lynchpin for making ISDN a commercial reality, because the new technology will remain beyond the reach of most users until it has been implemented in silicon. The current cost trend is therefore a welcome signal to the market that the new technology does have a promising future, and will help move the spotlight onto the work of the chip makers.