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
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ITU-T Study Group 17
Languages at SG17
Core Competencies at ITU-T
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Carrier class standards and specifications
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Quality of standards play a key role
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Experts and drivers in Telecommunications
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Strong organisational and logistic support by the
TSB
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Fast standards track
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We need to make even better standards faster
ITU-T Study Group 17
Mandate of ITU-T Study Group 17
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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
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
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ITU-T Study Group 17
The ITU-T language family (new)
DCL - Distribution and Configuration
Language
 URN - User Requirements Notation
 Incorporating Time and Performance into the
languages
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ITU-T Study Group 17
What makes the family different?
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Real-time, distributed communicating systems
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Formal, allowing verification and validation
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Many languages with a graphical syntax
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Commercial tool support
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Tool availability required for approval
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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
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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
Keep the edge
by concentrating on the
differentiating factors and
focusing on our strengths
ITU-T Study Group 17
ITU-T Languages
SDL
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Created for Telecommunications
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Centred around the specification of behaviour,
good for use in protocols
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Allows specification of structure and data
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Good tool support, including integration with
other techniques
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Widely used in standards and even more in
industry
Moving to other real-time application areas
ITU-T Study Group 17
SDL hot issues
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Upgrade of methodology
UML-MSC-ASN.1-SDL-TTCN
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CIF for SDL-2000
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MSC data mapping to SDL
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Time and performance features
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SDL as a UML profile (OMG?)
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SDL components for sale
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Gnu/Visual SDL??
ITU-T Study Group 17
ASN.1
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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
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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
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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 http://asn1.elibel.tm.fr/uses
Fully integrated in the formal languages SDL and
TTCN
ITU-T Study Group 17
MSC
Current Version:
Previous Version:
Next Version:
MSC 2000
MSC ’96
MSC 2004
Standard consists of:
• graphical grammar
• ASCII grammar
• static & dynamic semantics
• formal semantics, Annex B
• examples
ITU-T Study Group 17
MSC
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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.
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ITU-T Study Group 17
MSC Future Features
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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.
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ITU-T Study Group 17
A general purpose testing language
Conformance Testing
 Interoperability testing
 Robustness testing
 Performance testing
 regression testing
 System testing
 Integration testing, etc.
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ITU-T Study Group 17
TTCN-3: different presentation formats
Text format
Tabular
Format
TTCN-3
Core
Language
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MSC
Format
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Presentation
Format3
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Presentation
Formatn
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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
ITU-T Study Group 17
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
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ITU-T Study Group 17
What about XML?
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ASN.1 + XCN (XML Control Notation)
 as powerful and expressive as XSD (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 : http://asn1.elibel.tm.fr/links/#xml
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UML and XML
are easy and popular
SDL and ASN.1
support secure, hi-quality standards
You use the best of two worlds
ITU-T Study Group 17
The next years
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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
Helping you make better
standards faster
What ITU-Languages do for you
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Provide a method supported by commercial and free
tools
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Allow checking of syntactical and logical
(semantic) correctness on the fly
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Helps you check if the behaviour is what you
intended
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Improves the quality of the standard
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Interoperability is greatly improved
Once used properly, helps save time!
ITU-T Study Group 17
Obstacles to Language Use
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Benefit unclear
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Formality reduces freedom
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Check track record
Freedom only reduced for issues needed for
interoperation, use correct dose of formality
Quick and dirty is better
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This is not ITU-T‘s differentiator or unique
selling point
ITU-T Study Group 17
Obstacles to Language Use
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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
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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!
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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 ITUT languages
We really need permanent experts at ITU-T:
 ETSI success story
 Demand must come from users
ITU-T Study Group 17
ITU-T languages can help
ITU-T Recommendations
maintain or regain
competitive advantage
Support from Fora and Consortia
ASN.1 Consortium: http://www.asn1.org
 SDL Forum Society: http//www.sdlforum.org
 Indian SDL and TTCN Forum:
http://www.sdl-ttcnforum.org/
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ITU-T Study Group 17
ASN.1 Consortium
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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: http://www.asn1.org
ITU-T Study Group 17
ASN.1 – short summary
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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
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ASN.1 Types
& Values
Other types
& Values2
Other types
& Valuesn
TTCN-3
Core
Language
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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)
ITU-T Study Group 17
Major Elements of TTCN-3
TTCN-3 Core
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Data Types
Test Data
Test System
Architecture
Test
Behaviour
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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
ITU-T Study Group 17