Digital Private Network Signalling System: Difference between revisions

Revision as of 23:36, 5 August 2019

Revision as of 05:01, 3 November 2019

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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 [[Private Branch Exchange|PBX]]s. At the time, BT dictated what signalling could be used on its leased lines and, whilst it only had a minority interest in the sales of PBXs, was requested by the PBX manufacturers to produce a standard to prevent the creation of a plethora of conflicting PBX protocols being developed. 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 [[Plessey|Plessey PDX]] (a licensed version of the [[ROLM|ROLM CBX]]) and the GEC SL1 (a licensed version of the [[Northern Telecom]] SL1). It was recognised that corporate customers would wish to network these systems across the country. At the time, '[[Channel-associated signaling|CAS]]' inter node signaling was slow and inter-register signaling MF5, developed from [[PSTN]] signalling protocols, was complex and would not support sufficient features.

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

DPNSS was an active (and successful) collaboration between PBX manufacturers and BT which started relatively slowly (BT & Plessey) but quickly snowballed with [[Mitel|MITEL]], [[General Electric Company plc|GEC]], [[Ericsson]], [[Philips]] and eventually Nortel all joining to create a powerful and feature rich protocol.

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.