Plessey has added very advanced new features to its four-year-old ISDX digital PABX, including the ability to create virtual digital circuits using direct links to the System X public exchange, access computer data over X25 lines and make analogue lines act like digital lines. The company also says it is talking to Mercury Communications about it becoming a distributor of the product alongside British Telecom, Telephone Rentals, Plessey Communications Systems and Hull Telephone Co. Perhaps the most exciting new feature on the PABX is the ability for ISDX users to link directly to System X exchanges using the Digital Access Signalling System, DASS II protocol. DASS II links PABXs to Integrated Services Digital Networks, ISDNs, both public and private. This, for example, makes the star services for such things as conference calls on System X available to ISDX users on a private network. The protocol uses a 2Mbps link with 30 64Kbps voice+data channels and two 16Kbps channels, one for synchronisation and the other for signalling. The technology is ahead of its time and users will not be able to capitalise on it for a while: the exchange plant is not there yet – only about 5% to 10% of local exchanges have been converted to System X from TXE4 and even in the City only about 50% of systems are converted to System X. The other problem is that System X does not yet appear to be kitted out with DASS II. According to one industry spokesman, British Telecom cannot even give a quote for DASS II services until August so it is unlikely to be able to offer them until the beginning of 1988. Plessey also announced the availability of Analogue Private Network Signalling System, APNSS, a protocol that is particularly useful for companies with a small amount of digital PABX-to-PABX traffic, which does not justify the expense of leasing a 2Mbps digital link. Instead the user can lease a 4,800 baud data circuit and two modems and use an existing analogue line as a digital line. The company also introduced an X25 card for integrated packet switching to send and receive data. Plessey expects it to be used for remote terminal access to mainframes, communications between personal computers, local area network gateways and mainframes and access to Telecom’s Packet SwitchStream, PSS, and to private X25 networks. It costs around UKP15,000 to upgrade the existing ISDX software to incorporate the DASS II and APNSS services and an additional few thousand pounds for the integrated packet switching option. A new ISDX system costs around UKP300 per line and the terminal equipment to go with it costs between UKP30 for a basic telephone to UKP400 for the ISDT terminal. Plessey can only concentrate on the UK market in the short term, because it is one of the most advanced markets for ISDN and specifications are not yet standard across Europe. In addition US ISDN standards are not compatible with Europe. Plessey is still thinking of ways to get the ISDX into the US. The company has invested UKP40m in the product to date and claims to have installed over 1m lines. It is expecting a big increase in sales of its ISDT telephone terminal and it expects half its installed ISDX base to upgrade to the new system within two years. The ISDX represents about one sixth of Plessey Telecommunications’ UKP750m, business, which in turn contributes to 50% of the Plessey Co’s turnover.
