This can be point to point where the IP network carries packetised voice N x 64 Kbs speech and a separate IP signalling channel to carry the notional 64 Kbs of DPNSS signalling.

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.

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.

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.

Note that it is also possible to tunnel DPNSS and its associated PCM ( G711 ) over an IP network.

Some critics of DPNSS suggest that it is too loosely defined and allows too much latitude in its interpretation of message formats and timers.

The Digital Private Network Signalling System ( DPNSS ) is a network protocol used on digital trunk lines for connecting two PABX.

DPNSS was an active ( and successful ) collaboration between PBX manufacturers and BT which started relatively slowly ( BT & Plessey ) but quickly snowballed with MITEL, GEC, Ericsson, Phillips and eventually Nortel all joining to create a powerful and feature rich protocol.

DPNSS is a layer 3 protocol functioning as common channel signaling.

DPNSS is a compelled protocol in that each instruction issued must be met with an appropriate response from the other PBX otherwise the message is re-transmitted ( until timer expiry ).

For a protocol that began life in the 1980s, DPNSS is natively a long way from VoIP.

DPNSS was originally defined by British Telecom.

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.

There were also attempts ( during 1984 ) to take DPNSS into North America.

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 using analogue trunks ( Sometimes compressed ) and a modem to support D channel signalling.

) Levels 1-6 deal with simple call establishment ( make call / break call ) and are the minimum requirements by which a PBX can be said to be DPNSS compatible.

When setting up PBXs to run a DPNSS connection one end must be defined as the primary or ' A ' end.

However, many of the hybrid VoIP PBXs available from manufacturers worldwide provide on-board DPNSS trunk cards.

Commercially available equipment offers the ability to convert from DPNSS to Q. Sig.

It is also sometimes mistakenly believed that DPNSS is semi proprietary and that it is only possible to connect PBXs from the same manufacturer.

Experience indicates that this is not the case and BT's FeatureNet platform ( Nortel's DMS100 ) running DPNSS, has interconnected successfully to many PBX types available in the UK.

In addition, as part of the first commercial implementation of DPNSS ( in the Government Telephone Network or GTN in 1983 ), BT insisted that the core of the network be made from PBXs of different manufacture to prove the interoperability in real life.

He has a ship that can be rolled up like a tablecloth when not used, he relies on two talking ravens to gather intelligence, and he consults the talking head of a dwarf for prophecy ( he carries it around long since detached from its body ) ( Section 7 ).

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