1. International Telecommunication Union © ITU-T Study Group 17 Integrated Application of SDL Amardeo Sarma NEC Europe Ltd.

2. 2 © ITU-T Study Group 17 2003 SDL 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

3. 3 © ITU-T Study Group 17 2003 SDL – Focus o Basis Communicating extended finite state machines Since 1992 – Object-orientation o Relevant specification aspects Structure Types and Classes Behaviour Interfaces Data

4. 4 © ITU-T Study Group 17 2003 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

5. 5 © ITU-T Study Group 17 2003 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

6. 6 © ITU-T Study Group 17 2003 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

7. 7 © ITU-T Study Group 17 2003 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

8. 8 © ITU-T Study Group 17 2003 SDL – Focus Shift SDL Interpreted as C++ etc. Product used to create used to produce Specification Ideas Customer modelled by Design Engineers Design Implementation Software Engineers modelled by made as executes as Interpreted as Tools transformed by Focus Shift

9. 9 © ITU-T Study Group 17 2003 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

10. 10 © ITU-T Study Group 17 2003 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

11. 11 © ITU-T Study Group 17 2003 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

12. 12 © ITU-T Study Group 17 2003 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

13. 13 © ITU-T Study Group 17 2003 Where SDL can add value o Simulation and validation techniques shown effective to find conceptual and design bugs o Overall number of errors are reduced o Testing effort is reduced o Productivity increased, reducing cost o However, identify relevant application areas to avoid disappointments

14. 14 © ITU-T Study Group 17 2003 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