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A QoS Policy Modeling Language for Publish/Subscribe Middleware Platforms

A QoS Policy Modeling Language for Publish/Subscribe Middleware Platforms. Joe Hoffert, Doug Schmidt & Aniruddha Gokhale {jhoffert,schmidt,gokhale}@dre.vanderbilt.edu www.dre.vanderbilt.edu ISIS, Dept. of EECS Vanderbilt University Nashville, Tennessee June 21, 2007

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A QoS Policy Modeling Language for Publish/Subscribe Middleware Platforms

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  1. A QoS Policy Modeling Language for Publish/Subscribe Middleware Platforms Joe Hoffert, Doug Schmidt & Aniruddha Gokhale {jhoffert,schmidt,gokhale}@dre.vanderbilt.edu www.dre.vanderbilt.edu ISIS, Dept. of EECS Vanderbilt University Nashville, Tennessee June 21, 2007 DEBS 2007, Toronto, Canada www.dre.vanderbilt.edu

  2. Distributed Real-time & Embedded (DRE) Systems • Network-centric and large-scale “systems of systems” • e.g., industrial automation, emergency response • Different communication semantics • e.g., pub-sub • Satisfying tradeoffs between multiple (often conflicting) QoS demands • e.g., secure, real-time, reliable, etc. • Regulating & adapting to (dis)continuous changes in runtime environments • e.g., online prognostics, dependable upgrades, keep mission critical tasks operational, dynamic resource mgmt DRE systems increasingly realized via system composition of services

  3. Variability in the solution space (systems integrator role) • Diversity in platforms, languages, protocols & tool environments • Enormous accidental & inherent complexities • Continuous evolution & change Mapping problem artifacts to solution artifacts is hard Challenges in Realizing DRE Systems • Variability in the problem space (domain expert role) • Functional diversity • Composition, deployment and configuration diversity • QoS requirements diversity

  4. Application Application read write write Logical Data Store Application write write Application read read Application The OMG Data Distribution Service (DDS) • Provides flexibility, power and modular structure by decoupling: • Location – anonymous pub/sub • Redundancy – any number of readers & writers • Time – asynchronous, time-independent data distribution • Platform – similar to CORBA middleware • Architecturally Broken into: • Data Centric Publish/Subscribe (DCPS) • Lower layer APIs to exchange topic data based on QoS policies • Data Local Reconstruction Layer (DLRL) • Upper layer APIs that make topic data appear local

  5. QoS Policies Supported by DDS • DCPS entities (e.g., topics, data readers/writers) configurable via QoS policies • QoS tailored to data distribution in tactical information systems • Request/offered compatibility checked by DDS at Runtime • Consistency checked by DDS at Runtime • DEADLINE • Establishes contract regarding rate at which periodic data is refreshed • LATENCY_BUDGET • Establishes guidelines for acceptable end-to-end delays • TIME_BASED_FILTER • Mediates exchanges between slow consumers & fast producers • RESOURCE_LIMITS • Controls resources utilized by service • RELIABILITY (BEST_EFFORT, RELIABLE) • Enables use of real-time transports for data • HISTORY (KEEP_LAST, KEEP_ALL) • Controls which (of multiple) data values are delivered • DURABILITY (VOLATILE, TRANSIENT, PERSISTENT) • Determines if data outlives time when they are written • … and 15 more …

  6. Reliable data transfer requested Best effort data transfer offered Data will not be transferred X Deadline’s period = 5 ms. Time based filter’s minimum separation = 10 ms. X QoS policies will not be set QoS Policy Configuration Challenges • QoS Policy Compatibility • QoS policies for the communicating entities must be compatible between what’s requested and offered • QoS Policy Consistency • QoS policies for any one entity must be consistent with each other Need to flag errors earlier in the developmental lifecycle

  7. DDS QoS Modeling Language (DQML 1 of 2) Focus on “correct by construction” – check for errors at design-time • Models relevant DDS entities • Models DDS QoS polices as first class entities • Models relationships between entities and QoS policies

  8. QoS Settings QoS Settings DataReader DataWriter DDS QoS Modeling Language (DQML 2 of 2) • Supports QoS compatibility and consistency constraint checking • Generates implementation artifacts (currently for DDS Benchmarking Environment (DBE)) DBE Interpreter DBE

  9. Ongoing Work: DQML + Service Orchestration Work supported by DARPA PCES & ARMS Programs • CoSMIC tools e.g., PICML used to model application components, CQML for QoS • Captures the data model of the OMG D&C specification • Synthesis of static deployment plans for DRE systems • Capabilities being added for QoS provisioning (real-time, fault tolerance, security) CoSMIC can be downloaded at www.dre.vanderbilt.edu/cosmic

  10. QoS Settings QoS Settings Invoke the DBE Interpreter DBE DataReader DataWriter Concluding Remarks • QoS configuration management is a significant challenge for pub-sub systems • Need design-time tools to automate the QoS configuration management • Need tools to assure “correct-by-construction” systems • Model-driven Engineering is a promising approach

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