QSIG

Key takeaways

QSIG belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect QSIG to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of QSIG from memory before moving on to harder problems.

Reference excerpt

QSIG is an ISDN based signaling protocol for signaling between private branch exchanges (PBXs) in a private integrated services network (PISN). It makes use of the connection-level Q.931 protocol and the application-level ROSE protocol. ISDN "proper" functions as the physical link layer. QSIG was originally developed by Ecma International, adopted by ETSI and is defined by a set of ISO standard documents, so is not owned by any company. This allows interoperability between communications platforms provided by disparate vendors. QSIG has two layers, called BC (basic call) and GF (generic function). QSIG BC describes how to set up calls between PBXs. QSIG GF provides supplementary services for large-scale corporate, educational, and government networks, such as line identification, call intrusion and call forwarding. Thus for a large or very distributed company that requires multiple PBXs, users can receive the same services across the network and be unaware of the switch that their telephone is connected to. This greatly eases the problems of management of large networks. QSIG will likely never rival each vendor's private network protocols, but it does provide an option for a higher level of integration than that of the traditional choices.

List of QSIG standards Note: This list is not complete. See the "source" after the list for more information.

ECMA-143 - Private Integrated Services Network (PISN) - Circuit Mode Bearer Services - Inter-Exchange Signalling Procedures and Protocol (QSIG-BC), Basic Call, International and European Versions: ISO/IEC 11572, ETSI EN 300 172 ECMA-165 - Private Integrated Services Network (PISN) - Generic Functional Protocol for the Support of Supplementary Services - Inter-Exchange Signalling Procedures and Protocol (QSIG-GF), International and European Versions: ISO/IEC 11582, ETSI ETS 300 239 ECMA-164 - Private Integrated Services Network (PISN) - Inter-Exchange Signalling Protocol - Name Identification Supplementary Services (QSIG-NA), International and European Versions: ISO/IEC 13868, ETSI ETS 300 238 ECMA-174 - Private Integrated Services Network (PISN) - Inter-Exchange Signalling Protocol - Call Diversion Supplementary Services (QSIG-CF), International and European Versions: ISO/IEC 13873, ETSI ETS 300 257 ECMA-178 - Private Integrated Services Network (PISN) - Inter-Exchange Signalling Protocol - Call Transfer Supplementary Service (QSIG-CT), International and European Versions: ISO/IEC 13869, ETSI ETS 300 261 Source : ECMA - list of standards (search the list for PISN to find all QSIG related standards at ECMA) QSIG basically uses ROSE to invoke specific supplementary service at the remote PINX. These ROSE operations are coded in a Q.931 FACILITY info element. Here a list of QSIG opcodes:

List of ISDN standards

ETS 300 052 - Multiple Subscriber Number ETS 300 055 - Call Waiting ETS 300 092 - Calling Line Identification Presentation (CLIP) ETS 300 093 - Calling Line Identification Restriction (CLIR) ETS 300 097 - Connected Line Identification Presentation (COLP) ETS 300 098 - Connected Line Identification Restriction (COLR) ETS 300 130 - Malicious Call Identification ETS 300 141 - Call Hold ETS 300 172 - Circuit-Mode Basic Service ETS 300 173 - Called/Calling Line ID Presentation ETS 300 182 - Advice Of Charge ETS 300 188 - Three Way Conference ETS 300 207 - Call Diversion ETS 300 237 - Called/Calling Name Presentation ETS 300 238 - Called/Calling Name Presentation ETS 300 239 - Generic Functional Protocol ETS 300 256 - CFU Supplementary Service ETS 300 258 - Path Replacement (ANF-PR) ETS 300 359 - Call Completion To Busy Subscriber (CCBS) ETS 300 260 - Call Transfer By Join (SS-CT) ETS 300 261 - Call Transfer - (SS-CT) ETS 300 369 - Explicit Call Transfer ETS 300 745 - Message Waiting Indication (MWI) ETS 300 259 - Path Replacement Additional Network Feature (ANF-PR) ETS 301 258 - Recall Supplementary Service (SS-RE) ETS 301 919 - Single Step Call Transfer Supplementary Service (SS-SSCT) Source : European Telecommunications Standards Institute (ETSI)

CCITT G.703 - Describes the physical/electrical characteristics of hierarchical digital interfaces. Source : International Telecommunication Union (ITU)

Worked examples

Example 1 — a first encounter with QSIG

Start with the simplest possible case. Write down what QSIG claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to QSIG before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about QSIG ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of QSIG

In research: QSIG appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses QSIG in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: QSIG is common in secondary-school and first-year university syllabi. It links to neighbouring topics Telecommunication protocols, Telephony, so understanding it makes those chapters shorter.
In everyday life: Look for QSIG outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study QSIG in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what QSIG means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain QSIG out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is QSIG in simple terms?

QSIG is an ISDN based signaling protocol for signaling between private branch exchanges (PBXs) in a private integrated services network (PISN). It makes use of the connection-level Q.931 protocol and the application-level ROSE protocol.

Why does QSIG matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study QSIG?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on QSIG.