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Frequently Asked Questions on QSIG

1) What is QSIG?

See http://www.ecma-international.org/activities/Communications/QSIG_page.htm

2) What applications is QSIG typically used for?

QSIG can be used in all of the following applications:

  • Multi-vendor PBX networking
  • Attachment of ancilliary equipment (e.g., voicemail systems, paging equipment, wireless base stations) to a PBX network
  • Virtual Private Networks (VPN)
  • Broadband private networks
  • Linking Trans-European Trunked Radio (TETRA) areas
  • VoIP (H.323) applications.

3) How does QSIG differ from DPNSS?

QSIG is a protocol based closely on internationally agreed Standards for ISDN, whereas DPNSS is a protocol developed before the majority of ISDN standards were agreed and published. The fact that DPNSS is based on pre-ISDN technology in no way diminishes its usefulness and importance as a protocol around which highly featured and complex digital private networks can be built.

Both QSIG and DPNSS support similar sets of features.

4) What are the latest agreed specifications describing the QSIG protocol and where can they be obtained?

Ecma International has developed the entire set of QSIG standards and is now responsible for maintenance of those standards (including the QSIG standards published by ETSI and ISO/IEC).

Ecma Standards for QSIG are available free of charge from this website (http://www.ecma-international.org/activities/Communications/N-PISN.htm) or on a CD-ROM (http://www.ecma-international.org/publications/getit.php).

International Standards for QSIG are published by ISO/IEC and can be downloaded from http://isotc.iso.org/livelink/livelink/fetch/2000/2489/Ittf_Home/PubliclyAvailable
Standards.htm
.

European Standards for QSIG are available from ETSI, but in the main, these are just two page endorsements of the corresponding International Standards.

5) Are the published specifications for QSIG complete?

There is currently no work in progress to extend the set of QSIG specifications.

6) Will the name QSIG be the appropriate name in the future or will it be replaced by PSS1 (Private Signalling System no. 1)?

The formal name of the signalling system, as standardised at the Worldwide level by ISO / IEC is PSS1. The name QSIG was given to the signalling system when work on it first started in Europe in the late 1980s / early 1990s. It pre-dates the name given by ISO/IEC and is more widely known than that name. Both names will co-exist and QSIG will continue to be used as the marketing name.

7) What is the QSIG MoU?

The Memorandum of Understanding on the implementation of multi-vendor ISDN PBX networking (the QSIG MoU) took effect in 1994 and was intended to accelerate the development of PISN equipment using QSIG. The parties to the MoU are the 12 founding members (major PABX manufacturers) of the IPNS Forum. Major parts of the MoU were:

  • an agreement to implement a certain minimum set of functionality based on specific editions of several of the QSIG Standards, and
  • an undertaking to enter into interoperability testing with each other.

Significantly, the MoU said little about specific supplementary services to be implemented.

Today the specific Standards referred to by the MoU should be treated with caution by vendors considering the implementation of QSIG as they are no longer the latest versions.

8) I am looking for specific documentation on what QSIG features and functionality are supported by the products from a particular manufacturer. Can you help me?

In accordance with its own By-laws (Art.2.2) Ecma International shall be a non-profit-making organization and shall devote itself to no commercial activity whatsoever. Consequently, Ecma International is unable to offer advice on specific products.

9) Is it possible to interconnect E1 and T1 PABXs using QSIG signalling?

Yes, provided you have a E1 / T1 conversion unit and both PABXs support the same subset of QSIG.

10) I am trying to understand more about "Segmentation". What exactly is it for? How does it work?

Segmentation is a mechanism used by layer 3 protocols such as QSIG and DSS1 to split long messages so that each segment can be fitted into the payload of a layer 2 frame (e.g., a LAPD frame). The transmitting side splits (segments) the message and the receiving side re-assembles it. Annex ZA of ECMA-143, ISO/IEC 11572 or EN 300 172 contains the details. Some supplementary service APDUs, particularly when used in combination, can lead to the need for segmentation.

11) Is there an Additional Network Feature for accounting and billing?

No. The 3 ISDN AOC (Advice of Charge) services only report charges related to external calls (i.e., calls into a public network), and then only to the calling user's PABX.

12) In the case of a virtual private network, where a PABX is connected to the public network by a trunk that allows both public and private calls to be made, how does the public network distinguish between the public call and the private call?

The simplest method is to segregate private calls and public calls on different B-channels. Signalling associated with each group of channels can be carried on different channels or it can be carried on different data link connections within a single signalling channel.

Alternatively, a provision can be made in the signalling protocol to distinguish between calls intended for private network destinations (On-net calls) and calls intended for public network destinations (Off-net calls).

13) Are there any commercial testing services available for the QSIG protocol and do they cover Supplementary Services as well as Basic Call?

For costs reasons PBX manufacturers typically went for bilateral testing of QSIG signalling, but ETSI has published test specifications for some aspects of QSIG.

In accordance with its own By-laws (Art.2.2) Ecma International shall be a non-profit-making organization and shall devote itself to no commercial activity whatsoever. Consequently, Ecma International is unable to offer advice on specific services.

14) What test equipment (e.g., protocol analyzers) is available to assist with development of QSIG?

For costs reasons PBX manufacturers typically went for bilateral testing of QSIG signalling, but ETSI has published test specifications for some aspects of QSIG. Coverage of these tests may be an important evaluation criterion for certain categories of testing product.

In accordance with its own By-laws (Art.2.2) Ecma International shall be a non-profit-making organization and shall devote itself to no commercial activity whatsoever. Consequently, Ecma International is unable to offer advice on specific products.

15) What does the phrase "The layer 3 protocol at the Q reference point is visible at an interface at the C reference point" mean?

The QSIG protocol is used across a virtual or logical interface between 2 Call Control entities in different PINXs. The reference point describing this virtual or logical interface is the Q reference point. If it exists at all it is usually internal to a PINX. The only point at which you can physically see or "measure" the QSIG protocol is at the C reference point, which is usually a real interface between a PINX and, for example, a leased circuit. Thus, we say QSIG is visible at an interface at the C reference point.

16) What are Mapping functions?

A Mapping function "maps" the logical structure at the Q reference (i.e., DQ- and UQ-channels) to the physical structure at the C reference point. The physical structure at the C reference point depends on the particular scenario. It could be timeslots of a 2048 kbit/s leased circuit or it could be B-channels of a switched ISDN connection, etc. Thus, there is a different Mapping function used for each physical case.

17) What is the difference between a "Dedicated Physical Link" and a "Dedicated Transmission System"?

These terms are used in the descriptions of physical scenarios to which QSIG can be applied (ref: ECMA TR/57). A Dedicated Physical Link is simply a direct connection between 2 PINXs with no other transmission equipment involved. For example, if a company had 2 PINXs in the basement or on opposite sides of the street they might be directly connected. A Dedicated Transmission System is typically a circuit rented from a Telco to provide a connection over a longer distance e.g, between cities. It often contains additional multiplexing and cross-connect equipment.

18) Can I use QSIG over the PSTN?

QSIG is not designed to be used with traditional PSTN (i.e., analogue local loop) connections. However, if you include ISDN connections as being part of the PSTN, then QSIG can work across these between two PINXs (e.g., within a B-channel, within user-to-user signalling on the D-channel, or within the context of a VPN arrangement).

19) Can I use QSIG to carry voice over a packet-switched network e.g, VoIP?

Yes. Ecma TC32 TG17 http://www.ecma-international.org/memento/TC32-TG17.htm has produced Standards and Technical Reports on this subject.

20) Does QSIG support partial re-routeing?

Yes. If a Transit PINX has been implemented with "sufficient intelligence" it will be capable of intercepting a re-routeing invoke operation and becoming an End PINX for processing that operation. This allows the Transit PINX to re-route a call - which is termed "partial re-routeing".

21) Do I need to be a member of Ecma International to implement QSIG Standards?

Ecma Standards on QSIG, in common with all Ecma Standards, are open standards and can be implemented by anyone. There is no requirement to be a member of Ecma International or any other organisation in order to claim conformance to Ecma Standards.

Standardisation body Ecma International has developed the entire set of QSIG standards and is now responsible for maintenance of those standards (including the QSIG standards published by ETSI and ISO/IEC).


22) What is ATS-QSIG?

So-called "Air Traffic Services" QSIG is defined by Standard ECMA 312 "Private Integrated Services Network (PISN) - Profile Standard for the Use of PSS1 (QSIG) in Air Traffic Services Networks". ATS-QSIG uses the Low Delay Code-Excited Linear Prediction (LD-CELP) coding algorithm defined by ITU-T G.728 for the coding of voice in 16kbit/s sub channels. The Standard ECMA 253 defines the "Mapping Functions for the employment of 64kbit/s Circuit Mode Connections with 16kbit/s Sub-Multiplexing" used to transport three 16kbit/s voice sub-channels and one 16kbit/s signalling sub-channel in a single 64kbit/s bearer channel. ATS-QSIG is recommended by EUROCONTROL for use in ATS voice networks; further information may be obtained from http://www.eurocontrol.int

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