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QSIG is an ISDN based protocol for signalling between nodes of a Private Integrated Services Network (PISN). See our page on QSIG . In particular, QSIG allows products from different vendors to interwork together.
2. What applications is QSIG typically used for?
QSIG can be used in all of the following 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.
(Also see our page on DPNSS .)
4. Why don't we hear much about QSIG in the United Kingdom?
Because PABX manufacturers selling into the UK market have a vested interest in protecting their investments in DPNSS.
It is difficult to give a general answer as enhancements are being made all the time. Please contact us by email ( sales@pqmconsultants.com ) for an up-to-date answer.
International Standards for QSIG are published by and can be purchased from ISO/IEC .
European Standards for QSIG are available from ETSI , but in the main, these are just two page endorsements of the corresponding International Standards.
The majority of standards for QSIG are also available free of charge from ECMA, either by downloading from their website (http://www.ecma.ch) or on a CD-ROM ( email to helpdesk@ecma.ch ).
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.
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:
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.
Specific information on the features supported by each manufacturer is difficult to obtain as it is usually commercially sensitive. We have compiled a list (mainly of PABXs) in which the manufacturers are anonymous. This provides a good indication of the range of features supported.
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 information field of LAPD frames at layer 2. The transmitting side splits (segments) the message and the receiving side re-assembles it. Annex ZA of ETS 300 172, ECMA-143 or ISO/IEC 11572 contains the details. Increasingly, the length of supplementary service APDUs is becoming a concern. An enhancement to QSIG's Generic Functional Protocol will address this issue in the near future.
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. However, there are proprietary solutions available from some PABX manufacturers.
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).
One or two laboratories offer a commercial testing service, but these are restricted to tests of Basic Call functionality as far as we are aware.
14. What test equipment (e.g., protocol analyzers) is available to assist with development of QSIG?
All the usual manufacturers of telecoms protocol testing equipment claim to offer test equipment capable of assisting with QSIG development. Some pieces of equipment are better adapted than others and only a few support the special requirements of QSIG supplementary services.
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 it 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.
19. Can I use QSIG to carry voice over a packet-switched network e.g, VoIP?
Yes. ECMA is presently defining how QSIG can be used in scenarios where the Intervening Network and Interconnecting Network are IP networks.20. Can I use SNMP to manage a QSIG based network?
Yes. But there are no publicly available specifications for how to do this.21. 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".Home Page | What We Do | Corporate Networks | Publications | Contact Us
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