Implementation Challenges in Real-Time Middleware for Distributed Autonomous Systems

1. Implementation Challenges in Real-Time Middleware forDistributed Autonomous Systems Prof. Vincenzo Liberatore Research supported in part by NSF CCR-0329910, Department of Commerce TOP 39-60-04003, NASA NNC04AA12A, a Lockheed grant, an ABB contract, and an OhioICE training grant.

2. Motivation • Sustainable presence on planetary surface • Human-robotic missions • E.g., construction, maintenance • Consequences • Higher performance • Earth tele-operation inappropriate for construction • Multiple assets • Communication and coordination • Autonomous Distributed System

3. Potential Scenario (Teleops) • Tele-operations • Robots, rovers • Pressurized vehicles • Requirements • Single- or multi-hop • End-point adaptation to network non-determinism • Quality-of-Service • System and control metrics Lunar Relay 4-6 Humans on EVA Autonomous Robot Pressurized Vehicle Repeater Surface Terminal Teleoperated Robot Lander (Later Habitat)

4. Talk Overview • Bandwidth allocation • Play-back buffer • Quality-of-Service (QoS) • DRE implementation • Conclusions

5. Bandwidth Allocation • Objectives: • Stability of control systems • Efficiency & fairness • Fully distributed, asynchronous, & scalable • Dynamic & self reconfigurable

6. Problem Formulation • Define a utility fn U(r) that is • Monotonically increasing • Strictly concave • Defined for r ≥ rmin • Optimization formulation

7. p p p Distributed Implementation • Two independent algorithms • End-systems (plants) algorithm • Router algorithm (later on) NCS Plant NCS Controller Router

8. Determination of kpand ki • Stability region in the ki–kp plane • Stabilizes the NCS-AQM closed-loop system for delays less or equal d • Analysis of quasi-polynomials, f(s,es)

9. 50NCS Plants: Simulations & Results [Branicky et al. 2002] [Zhang et al. 2001]

10. Simulations & Results (cont.) PI ¤ P ¤

11. Talk Overview • Bandwidth allocation • Play-back buffer • Quality-of-Service (QoS) • DRE implementation • Conclusions

12. Flow Sensor data Remote controller Control packets Timely delivery Stability Safety Performance Information Flow

13. Main Ideas • Predictable application time • If control applied early, plant is not in the state for which the control was meant • If control applied for too long, plant no longer in desired state • Keep plant simple • Low space requirements • Integrate Playback, Sampling, and Control

14. Algorithm • Send regular control • Playback time • Late playback okay • Expiration • Piggyback contingency control

15. Plant output Open Loop Play-back

16. Packet losses Figure 8

17. Talk Overview • Bandwidth allocation • Play-back buffer • Quality-of-Service (QoS) • DRE implementation • Conclusions

18. Network Quality-of-Service (QoS) • Support real-time distributed applications • Voice, video • Networked control • Guarantees • Network metrics • Bandwidth • Delays • Delay jitter • Loss rates • End-point metrics • Tracking in networked control • Example • Packet priorities • Current support in Internet • Significant research and development • None of the above: best-effort

19. QoS and Space Networks • Examples • Human-robotic missions necessitate real-time communication • QoS no longer only for commercial satellite network • Fully Distributed QoS [IWQoS 2004] • Local mechanisms to protect from global congestion risks • Addition to planned QoS • Autonomously adaptable to QoS requirements with no human supervision • Protects from error in networks configuration • Suitable for Distributed Autonomous systems • Higher performance • On the flight

20. Videos: Tele-Operation, Cross-Traffic and Distributed QoS The following videos were made possible by NASA funds provided by GRC under Contract NNC05CB20C Note: video not included in SMC-IT proceedings

21. Distributed QoS • Definition • Local mechanisms to protect from global risk • Deployment and benefits • Addition to planned QoS • Autonomously adaptable to QoS requirements with no human supervision • Protects from error in networks configuration • Suitable for Distributed Autonomous systems • Higher performance • On the flight

22. Talk Overview • Bandwidth allocation • Play-back buffer • Quality-of-Service (QoS) • DRE implementation • Conclusions

23. Middleware implementation • Sophisticated commercial DRE • Issues • Embedded devices with limited memory, computation, power • Support for real-time protocols • Support for network QoS • Incorporate research contributions • E.g., bandwidth allocation, buffers • On-going work

24. Talk Overview • Bandwidth allocation • Play-back buffer • Quality-of-Service (QoS) • DRE implementation • Conclusions

25. Conclusions • Sustainable presence on planetary surface • Human-robotic missions • E.g. construction, maintenance • Needs • Higher performance • Multiple assets • Implications • Network research • Distributed QoS • Middleware research • Resource allocation • Buffers • Embedded implementation • Middleware research and development fits between • Networks • Intelligent systems