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

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.

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.

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.

DASS2 is an improved version over DASS1, based on experiences with DPNSS.

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.

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.

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.

DPNSS carries its protocol messages as short strings of IA5 text.

A lightweight version of DPNSS ' APNSS ' was developed using analogue trunks ( Sometimes compressed ) and a modem to support D channel signalling.

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 originally defined by British Telecom.

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.

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.

) 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.

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.

They are huge areas which have been swept by winds for so many centuries that there is no soil left, but only deep bare ridges fifty or sixty yards apart with ravines between them thirty or forty feet deep and the only thing that moves is a scuttling layer of sand.

This is a phenomenon familiar to all radio listeners, resulting from reflection of skywave signals at night from the ionized layer in the upper atmosphere known as the ionosphere.

Thermoforming the laminate and then sanding away the top layer is a quick and economical way to produce a two-color sign.

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The ovum is at first rigidly held but in fertilised eggs, the innermost layer liquefies and allows the embryo to move freely.

Each course is laid the whole length of the wall, overlapping at the corners on a layer of adobe mortar.

Following each individual brick should be a layer of adobe mortar, recommended to be at least an inch thick to make certain there is ample strength between the brick ’ s edges and also to provide a relative moisture barrier during the seasons where the arid climate does produce rain.

The lower the layer the worse it is.

In general, external alpha radiation is not harmful since alpha particles are effectively shielded by a few centimeters of air, a piece of paper, or the thin layer of dead skin cells.

The thick inner layer of the shell is composed of nacre or mother-of-pearl, which in many species is highly iridescent, giving rise to a range of strong and changeable colors, which make the shells attractive to humans as decorative objects, and as a source of colorful mother-of-pearl.

Often, the fact that sometimes only a thin surface layer of violet color is present in the stone or that the color is not homogeneous makes for a difficult cutting.

Much of the ACC transport is carried in this front, which is defined as the latitude at which a subsurface salinity minimum or a thick layer of unstratified Subantarctic Mode Water first appears, allowed by temperature dominating density stratification.

AEP ( AppleTalk Echo Protocol ) is a transport layer protocol designed to test the reachability of network nodes.

: The outermost layer, the zona glomerulosa is the main site for production of mineralocorticoids, mainly aldosterone, which is largely responsible for the long-term regulation of blood pressure.

It can be a raw bitstream, but it is usually a container format or an audio data format with defined storage layer.

In a semiconductor diode, the anode is the P-doped layer which initially supplies holes to the junction.

In such models, the behavior of the adhesive layer itself is neglected and only the adherents are considered.

Specifically, at speeds of OC-3 and above, the cost of segmentation and reassembly ( SAR ) hardware makes ATM less competitive for IP than Packet Over SONET ( POS ); because of its fixed 48-byte cell payload, ATM is not suitable as a data link layer directly underlying IP ( without the need for SAR at the data link level ) since the OSI layer on which IP operates must provide a maximum transmission unit ( MTU ) of at least 576 bytes.