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The Language Family @ ITU-T. Amardeo Sarma Co-Chairman, ITU-T Study Group 17. Contents. Languages at SG17 ITU-T Languages SDL ASN.1 MSC TTCN Helping you make better standards faster. Languages at SG17. Core Competencies at ITU-T. Carrier class standards and specifications

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The language family @ itu t

The Language Family @ ITU-T

Amardeo SarmaCo-Chairman, ITU-T Study Group 17


  • Languages at SG17

  • ITU-T Languages

    • SDL

    • ASN.1

    • MSC

    • TTCN

  • Helping you make better standards faster

ITU-T Study Group 17

Core competencies at itu t
Core Competencies at ITU-T

  • Carrier class standards and specifications

    • Quality of standards play a key role

  • Experts and drivers in Telecommunications

  • Strong organisational and logistic support by the TSB

  • Fast standards track

    • We need to make even better standards faster

ITU-T Study Group 17

Mandate of itu t study group 1 7
Mandate of ITU-T Study Group 17

  • Responsible for technical languages, the methods for their usage and other issues related to the software aspects of telecommunication systems.

  • Studies on modelling, specification and description techniques and on other software aspects in line with the requirements of and in co-operation with the relevant other Study Groups (4,11,13,16).

  • SG17 is Lead Study Group on Languages and Description Techniques within ITU-T

  • SG 17 Policy: Strong coupling with industrial needs and use

ITU-T Study Group 17

The itu t language family
The ITU-T language family

  • SDL - Specification and Description Language

  • MSC - Message Sequence Chart

  • ODL - Object Definition Language (adopted from TINA)

  • ASN.1 - Abstract Syntax Notation One

  • TTCN Tree and Tabular Combined Notation

  • CHILL - CCITT HIgh-Level Language

ITU-T Study Group 17

The itu t language family new
The ITU-T language family (new)

  • DCL - Distribution and Configuration Language

  • URN - User Requirements Notation

  • Incorporating Time and Performance into the languages

ITU-T Study Group 17

What makes the family different
What makes the family different?

  • Real-time, distributed communicating systems

  • Formal, allowing verification and validation

  • Many languages with a graphical syntax

  • Commercial tool support

    • Tool availability required for approval

    • Tools vendors directly involved in work

  • Catering for users both in Industry and in Standards bodies (SDOs), e.g. ITU-T SG 11

ITU-T Study Group 17

Language usage
Language Usage

  • Initially, languages were mainly aimed at standards and Recommendations

  • For the core languages, industrial use has today far outgrown use in standards!

  • The use at SDOs is below the potential to:

    • Improve quality of standards

    • Reduce time

  • But: Use requires some investment

  • Fora support ASN.1, SDL, MSC and TTCN

ITU-T Study Group 17

Our strategy at itu t sg 17
Our Strategy at ITU-T SG 17

Keep the edgeby concentrating on thedifferentiating factors and focusing on our strengths

ITU-T Study Group 17


  • Created for Telecommunications

    • Centred around the specification of behaviour, good for use in protocols

    • Allows specification of structure and data

    • Good tool support, including integration with other techniques

    • Widely used in standards and even more in industry

  • Moving to other real-time application areas

ITU-T Study Group 17

Sdl hot issues
SDL hot issues

  • Upgrade of methodologyUML-MSC-ASN.1-SDL-TTCN

  • CIF for SDL-2000

  • MSC data mapping to SDL

  • Time and performance features

  • SDL as a UML profile (OMG?)

  • SDL components for sale

  • Gnu/Visual SDL??

ITU-T Study Group 17

Asn 1

  • International standard : ITU-T X.680 to X.683 | ISO/IEC 8824-1 to 4 with a sizeable base of tools that support ASN.1

  • Describes data exchange between two communicating applications

  • Several associated standardized encodings, such as:

    • efficient (binary) encoding: Packed Encoding Rules (PER)

    • canonical encoding for digital signatures:Distinguished Encoding Rules (DER)

    • XML (textual) encoding rules (XER) with tool support

  • Mature, long record of reliability and interoperability

  • ASN.1 is a critical part of our daily lives; it's everywhere, but it works so well it's invisible!

ITU-T Study Group 17

Asn 1 and the telecom industry
ASN.1 and the telecom industry

  • Intelligent network

  • GSM

  • UMTS (3G cellphones)

  • Voice over IP

  • Interactive television

  • Videoconference

  • SET, C-SET (secured electronic transaction:e-commerce, m-commerce)

  • Computer-supported telecommunications applications

  • ...

ITU-T Study Group 17

Asn 1 in other domains
ASN.1 in other domains

  • Intelligent transportation

  • Radio-frequency identification (RFID)

  • ATN (Aeronautical Telecommunication Network)

  • Embedded systems

  • Financial operations (ASC X.9, ISO TC 68)

  • Control of manufacturing systems

  • And a lot of other application domains:see

  • Fully integrated in the formal languages SDL and TTCN

ITU-T Study Group 17



  • Current Version: MSC 2000

  • Previous Version: MSC ’96

  • Next Version: MSC 2004

  • Standard consists of:

  • graphical grammar

  • ASCII grammar

  • static & dynamic semantics

  • formal semantics, Annex B

  • examples

ITU-T Study Group 17


  • MSC-2000 is a rich language with rigorously defined semantics, unlike UML sequence charts

    • One of the advantages over competitors

  • MSC is widely, but informally, used often independently of other notations.

    • At IETF, MSC is clearly a candidate to formalise signal flows

  • There is scope for increased tool/language penetration.

  • Users are often unaware of Z.120 as a standard for sequence diagrams and that MSC has good tool support.

ITU-T Study Group 17

Msc future features
MSC Future Features

  • Message Channels

  • Presentation Formats

    • TTCN Graphical presentation format, Z.142

    • semantic restrictions, e.g. tracing

  • Instantiations of Universal Data Interface

    • SDL interface scheduled 2002, Z.121

    • ASN.1 interface?

    • TTCN-3 interface?

  • UML alignment

    • OMG UML v2.0 sequence diagrams

ITU-T Study Group 17

Ttcn 3

  • Testing and Test Control Notation TTCN-3 is used to write detailed test specifications

  • Applicable to telecom and datacom testing

  • Application Areas

    • protocols

    • services

    • APIs

    • software modules etc.

ITU-T Study Group 17

A general purpose testing language
A general purpose testing language

  • Conformance Testing

  • Interoperability testing

  • Robustness testing

  • Performance testing

  • regression testing

  • System testing

  • Integration testing, etc.

ITU-T Study Group 17

Ttcn 3 different presentation formats

Text format

Tabular Format

MSC Format



TTCN-3: different presentation formats

  • Core format is a text based language

  • Core can be viewed as text or in various presentation formats

  • Tabular format for conformance testing

  • Message Sequence Chart (MSC)format

  • Other standardized formats in the future

  • Proprietary formats

TTCN-3 Core Language

ITU-T Study Group 17

What about uml
What about UML?

  • SDL and MSC experts key for UML 2.0

  • Tools for joint support available

  • UML without SDL is like a car without an engine

  • Co-operation with OMG in progress

  • If you really want UML, you can use it without losing the benefits of SDL/MSC

ITU-T Study Group 17

What about xml
What about XML?

  • ASN.1 + XCN (XML Control Notation)

    • as powerful and expressive asXSD (XML Schema Definition)

    • less verbose and much more readable.

  • ASN.1 is a mature schema notation for XML. No schema mapping is needed

  • ASN.1/XER: efficient binary encodings with XML (+ XSL)display (or transfer if needed)

  • CXER èASN.1/XER as a canonical variant of XER for secured transactions

  • XER tools :

ITU-T Study Group 17

UML and XMLare easy and popular

SDL and ASN.1support secure, hi-quality standards

You use the best of two worlds

ITU-T Study Group 17

The next years
The next years

  • After UML 2.0, work together towards

    • Powerful, new versions of SDL and MSC

    • Strong bridges to ASN.1 and TTCN in addition to UML

  • Consolidate and strengthen the use of languages in Telecommunications

  • Expand further into new domains

  • Focus on penetrating the IETF in the coming years

  • Support standardisation and education with tools

ITU-T Study Group 17

What itu languages do for you
What ITU-Languages do for you

  • Provide a method supported by commercial and free tools

  • Allow checking of syntactical and logical (semantic) correctness on the fly

  • Helps you check if the behaviour is what you intended

  • Improves the quality of the standard

    • Interoperability is greatly improved

  • Once used properly, helps save time!

ITU-T Study Group 17

Obstacles to language u se
Obstacles to Language Use

  • Benefit unclear

    • Check track record

  • Formality reduces freedom

    • Freedom only reduced for issues needed for interoperation, use correct dose of formality

  • Quick and dirty is better

    • This is not ITU-T‘s differentiator or unique selling point

ITU-T Study Group 17

Obstacles to language u se1
Obstacles to Language Use

  • No expertise in group

    • Specialists should concentrate on their domain – get support for languages

  • No time

    • Check whether overall time is lost or gained

  • Missing support

    • TSB should provide this!

    • Or ask SG17 – we could e.g. provide tutorials in SDL, ASN.1 etc.

ITU-T Study Group 17

Tool usage at itu t
Tool usage at ITU-T

  • SDT is currently the standard tool at ITU and ETSI

  • Recommendation authors send SDT files, which are checked by TSB staff

  • Formal descriptions are considered non-coprighted

  • Common Interchange Format CIF is very important (e.g. for those using Cinderella)!

  • Availability of cheap or free lightweight tool for standards greatly helps promote SDL/MSC

    • The ITU-T CD-ROM, also available for you all, has been a step in this direction!

ITU-T Study Group 17

Professional support is needed
Professional support is needed!

  • To further improve standards quality, SG17 reinforced the recommendation that TSB provide

    • expertise on a regular basis in the ITU-T languages and methodologies concerning the use of the languages

    • tools, supporting and facilitating the use of ITU-T languages

  • We really need permanent experts at ITU-T:

    • ETSI success story

    • Demand must come from users

ITU-T Study Group 17

Support from fora and consortia
Support from Fora and Consortia regain competitive advantage

  • ASN.1 Consortium:

  • SDL Forum Society: http//

  • Indian SDL and TTCN Forum:

ITU-T Study Group 17

Asn 1 consortium
ASN.1 Consortium regain competitive advantage

  • Group of ASN.1 users (people and companies), specifiers and tool-vendors

  • Share resources and information

  • Promote ASN.1 (towards newspaper and journals, companies, universities…)

  • No standardization work

  • Three forums:

    • Industry forum

    • Standardization forum

    • Academic forum

  • Website:

ITU-T Study Group 17

Asn 1 short summary
ASN.1 – short summary regain competitive advantage

  • Robust and stable technology that has withstood the test of time, and which continues to improve over time.

  • Now supports XML in ITU-T X.693 (XML Encoding Rules)

  • An easier schema for XML than W3C XML Schema (XSD)

  • Makes it possible to use XML where it currently is impossible due to XML's verbose size

  • ITU-T X.694 now makes it possible to convert XSD to ASN.1

  • A sizeable base of tools that support ASN.1, including PER and XML, now exists

  • The rapid degree of ASN.1:2002 features implemented by tool vendors is a testament to the strength of the ASN.1 industry.

ITU-T Study Group 17

Ttcn 3 and other languages

ASN.1 Types & Values regain competitive advantage

Other types & Values2

Other types & Valuesn

TTCN-3 and Other Languages

  • TTCN can be integrated with other 'type and value' systems

  • Fully harmonized with ASN.1 (1997)

  • Harmonization possible with other type and value systems (possibly from proprietary languages)

TTCN-3 Core Language

ITU-T Study Group 17

Major elements of ttcn 3

Test System Architecture regain competitive advantage

Test Data

Data Types

Test Behaviour

Major Elements of TTCN-3

  • Built-in and user-defined generic data types (e.g., to define messages, service primitives, information elements, PDUs)

  • Actual test data transmitted/received during testing

  • Definition of the components and communication ports that are used to build various testing configurations

  • Specification of the dynamic test system behaviour

TTCN-3 Core

ITU-T Study Group 17