International Telecommunication Union
Integrated Application
of SDL
Amardeo Sarma
NEC Europe Ltd.
© ITU-T Study Group 17
SDL
process
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o Graphical specification language with a formal basis
o Allows early detection of errors and functional
validation prior to implementation
o Widely used for protocol standards and in the telecoms
industry
o Strong use as a high-level implementation language with
code generation
o SDL played a major role in the standardisation of UML
2.0
© ITU-T Study Group 17 2003
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SDL – Focus
o Basis
• Communicating extended finite state
machines
• Since 1992 – Object-orientation
o Relevant specification aspects
• Structure
• Types and Classes
• Behaviour
• Interfaces
• Data
© ITU-T Study Group 17 2003
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SDL – Strengths and Weaknesses
o Strengths
• Formal basis, enables
• Verification and validation
• simulation
•
•
•
•
Widely used in telecom domain
Graphical syntax
Object-orientation
Tool support
o Weaknesses
• Not much used in the Internet world
• Usefulness of formality questioned
• Learning curve
• Missing tool alternatives
© ITU-T Study Group 17 2003
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SDL is the choice when ..
o Real-time systems that communicate, e.g.
via protocols, are used
o Quality is an issue:
• Verification of consistency
• Validation of behaviour
o The state-machine approach seems natural
in the application domain
o Protocol specifications that are needed are
already available as SDL
o Experience in the successful use of SDL
already exists
© ITU-T Study Group 17 2003
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SDL: Application domain
o Specification to Implementation -
broad spectrum
• Products - procurement, design,
interface description
• Standards - behaviour, conformance
models
o Real Time Systems - discrete, reactive
• Not specifically telecommunications,
e.g. also automotive and aerospace
• Protocols and Services
© ITU-T Study Group 17 2003
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SDL – Focus shift
o from analysis and specification levels
to design and implementation
o from more abstract to more concrete
levels
o from being developed primarily for
other standards to being a software
development language
o towards a more generic language for
other real-time aspects
© ITU-T Study Group 17 2003
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SDL – Focus Shift
Specification
Focus Shift
Ideas
Customer
used to
create
modelled by
Design
SDL
Design
Interpreted as
Implementation
Engineers
used to
produce
Tools
Engineers
Software
executes
as
© ITU-T Study Group 17 2003
transformed
by
C++ etc.
Product
8
Use of SDL – SW development
o Design language
• Telecom, automotive, aerospace
• Real-time systems
• Protocol design
• Early validation and simulation
o Implementation language
• SDL as a high-level implementation
language
• Combine with MSC, TTCN, C, ..
• Automatic code generation
© ITU-T Study Group 17 2003
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SW development areas
o Terminals
o Switching systems
o General networking components
o Network Management
o GSM and UMTS
o Automotive and aerospace
o Intelligent Networks
o Datacoms
© ITU-T Study Group 17 2003
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Use in Standards
o ITU-T – traditionally strong
• Protocols in SG11
• Intelligent Networks – Success Story
• Few new protocols these days
o GSM and UMTS (3GPP)
• New strong field, but
• SDL use not comprehensive
o IETF
• Isolated uses, e.g. OSPF, but big potential
• Requirement for textual form in standards
• Auxilliary use – as in OSPF – is a perspective
© ITU-T Study Group 17 2003
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Obstacles for use
o Current practices, learning curve
o Competition with hype languages
o Lacking expertise and support, e.g. in SDOs
o NIH and not-our-language syndrome
o Availability of Public Domain tools
o Cost of tools
o Perceived risk, e.g. integration with other
languages
o Delay of “first” project
Obstacles can be overcome
© ITU-T Study Group 17 2003
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Where SDL can add value
o Simulation and validation techniques
o
o
o
o
shown effective to find conceptual
and design bugs
Overall number of errors are reduced
Testing effort is reduced
Productivity increased, reducing cost
However, identify relevant application
areas to avoid disappointments
© ITU-T Study Group 17 2003
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Important future issues
o Extend application areas, especially related
to the Internet
o For some years, consolidation, not further
extension of the language, must be the
focus – Users need to be able to follow
o Focus SDL on design and implementation
o Integration with other techniques
• ASN.1
• UML
o Maintain formality and state machine
concept as the distinguishing factor
© ITU-T Study Group 17 2003
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