Developing Reliable Systems with SDL Design Patterns and Design Components Christian Webel, Ingmar Fliege, Alexander Geraldy, Reinhard Gotzhein University of Kaiserslautern {webel, fliege, geraldy, gotzhein}@informatik.uni-kl.de

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Developing Reliable Systems withSDL Design
Patterns and Design ComponentsChristian
Webel, Ingmar Fliege, Alexander Geraldy,Reinhard
GotzheinUniversity of Kaiserslauternwebel,
fliege, geraldy, gotzhein_at_informatik.uni-kl.de
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Topics

1. Motivation
2. SDL Design Patterns
3. Micro Protocols
4. Comparison
5. Example Airship Control
6. Conclusion

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1. Motivation

• Problem
• solution from scratch
• existing systems lack of reliability
• difficult to integrate reliability
• Solution
• defining SDL design patterns and design
  components
• using these software artefacts to augment system
  reliability step-by-step
• reuse
• SDL as a design language to develop reliable
  systems

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1. Motivation

• Concepts
• Reliability
• ability of a system to perform its tasks under
  given conditions for a certain period of time
• Watchdog
• component or functionality monitoring the
  operation of a system by observing an
  alive-signal
• Heartbeat
• component or functionality sending a periodic
  alive-signal

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2. Adding Reliability through SDL Design Patterns

• generic solution for recurring design problems
• reusable software artefact
• SDL as design language
• to be selected, adapted and embedded

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2. Adding Reliability through SDL Design Patterns

• B provides data for A
• B needs to be monitored by A
• A is refined by applying the Watchdog pattern
• B by applying the Heartbeat pattern

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2. Adding Reliability through SDL Design Patterns

• Design pattern Watchdog

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2. Adding Reliability through SDL Design Patterns

• Design pattern Heartbeat

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3. Adding Reliability through Micro Protocols

• encapsulate a single (distributed protocol)
  functionality using a specific mechanism
• self-contained and ready-to-use
• well-defined interfaces (operators)
• can be composed yielding macro protocols

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3. Adding Reliability through Micro Protocols

• A, B, Watchdog and Heartbeat as described
• ready-to-use solutions, no modifications within A
  or B needed
• useful if A or B cannot or should not be modified
  (e.g. 3rd party components)

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3. Adding Reliability through Micro Protocols

• Micro protocol
• Watchdog
• one single process type
• may be refined to match the requirements of the
  embedding context
• needs a periodic trigger alive

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3. Adding Reliability through Micro Protocols

• Micro protocol
• Heartbeat
• one single process type
• may be refined to match the requirements of the
  embedding context
• provides a periodic trigger alive

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4. Comparison

• Design Patterns vs.
  Micro Protocols

Advantages Advantages
no change of the system architecture necessary optimization of heartbeat traffic reusable solution no change of the behaviour of the other system components necessary ready-to-use solution reusable solution
Disadvantages Disadvantages
engineering knowledge required change of the system architecture necessary
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5. Example Airship Control

• application to control an airship via WLAN
• two parts
• airshipClienttransmits the control values to the
  airship
• airshipServerreceives the values and controls
  the airship hardware
• reliability is needed !!!

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5. Example Airship Control

• Application of the Heartbeat pattern

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5. Example Airship Control

• Application of the Watchdog pattern

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5. Example Airship Control

• Using the Watchdog and Heartbeat Micro Protocols
• selected and glued together
• Watchdog
• redefine timeout-transition
• add stop-transition
• Heartbeat
• just select and integrate
• also possible to use design patterns und micro
  protocols together

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6. Conclusion

• systematic approach to augment existing systems
  with reliability aspects
• reuse and reliability (design patterns, micro
  protocols)
• Outlook
• Validation
• Compositional testing
• Each component tested
• Resulting system tested for composition faults
• Developing more micro protocols
• QoS, Routing, Scheduling, Medium Access, Flow
  Control,

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• Thank you for your attention!
• Questions?