Digital Private Network Signalling System: Difference between revisions

Revision as of 10:12, 9 April 2011

Revision as of 10:17, 9 April 2011

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==History==

DPNSS was developed in the early 1980s by BT, or its forerunner, Post Office Telecommunications in recognition that the emerging Digital Private Circuit Primary Rate product 'Megastream' had to address the market for both data and voice, the latter being significantly greater because of the market for PBXs. It may seem odd now{{Says who|date=April 2011}} that BT would invest in the development of a signaling protocol for PBXs in which it had a minority interest and in competition with its PSTN services. Under the liberalization rules of the day (1979), BT was barred from manufacturing, selling or supplying PBXs of more than 200 extensions. Digital (PCM-based) PBXs were just starting to come into the marketplace with the ROLM/Northern Telecom SL1, and Plessey PDX, it was recognised that corporate customers would wish to network these systems across the country. At the time, 'CAS' inter node signaling was slow and inter-register signaling MF5, developed for the PSTN, was complex and would not support sufficient features.

The support for DPNSS as BT's own signaling protocol also differentiated BT's private circuit’s services from those of its emerging rival Mercury Communications.

In practice, DPNSS was possibly a backroom development by a couple of guys at BT's research labs whose efforts accidentally found a market and official support.{{FactCitation needed|date=April 2011}}

BT and some of the UK manufacturers championed DPNSS into ECMA and CCITT (ITU) but it was eventually deprecated by the standards bodies in favour of Q931 and QSig. Nevertheless, the elegance of the protocol and its compatibility with PBX features ensured the adoption DPNSS actually grew in Europe, compared to the much slower take-up of Qsig.

Version 1 of BTNR188 (DPNSS) was issued in 1983; the last version of DPNSS to be released 6 in 1995 included compatibility with ISDN features released in V5. A lightweight version of DPNSS 'APNSS' was developed for smaller PBXs.