Expected-Reliability Analysis for Wireless CORBA with Imperfect Components

1. Expected-Reliability Analysis for Wireless CORBA with Imperfect Components Xinyu Chen and Michael R. Lyu Department of Computer Science and Engineering The Chinese Univ. of Hong Kong

2. Handoff: a mechanism for a Mobile Host to seamlessly change a connection from one Access Bridge to another Access Bridge Mobile Host Static Host Wired Link Radio Link Cell Home Location Agent Wireless CORBA Architecture Wired Network

3. Outline • Background • Definitions and assumptions • Expected-reliability analysis for different communication schemes • Conclusions

4. Reliability • T – a random variable representing the lifetime of a component • f(t) – the probability density function of T • R(t) – the reliability function of the component

5. Mean Time to Failure (MTTF) • Mean Time to Failure (MTTF) • the expected value of the lifetime T

6. 7 1 S 3 4 6 T 2 5 Two-Terminal Reliability in Wired Networks • Assumption: • Nodes or links experience failures • The probability that there exists an operating path from a source node to a target node

7. Why Expected-Reliability • Terminal mobility introduces handoff • Handoff causes the change of number and type of engaged communication components, then results in different system states

8. Expected-Reliability • Two-terminal expected-reliability at time t • Qs(t) • the probability of the system in state s at time t • Rs(t) • the reliability of the system in state s at time t • Mean Time to Failure

9. Assumptions • There will always be a reliable path in the wired network • The wireless link failure is negligible • All the four components, AB, MS, SH, and HLA, of wireless CORBA are failure-prone and fail independently

10. The Reliability of the System in State s at Time t • Rs(t) • n(s) – the number of engaged components in system state s • Ri(t) – the reliability of the ith component • c – the type of a component • mh, ab, sh, or hla • kc(s) – the number of component c in state s

11. Assumptions (cont’d) • The failure parameters for the four components, MH, AB, SH, and HLA, are constant, which are , , , and , respectively • The MH’s sojourn time with an AB and the handoff completion time are exponentially distributed with parameters  and , respectively

12. Four Communication Schemes • Static Host to Static Host (SS) • a traditional communication scheme • Mobile Host to Static Host (MS) • Static Host to Mobile Host (SM) • Mobile Host to Mobile Host (MM)

13. The MS Scheme

14. The System State Probability

15. Expected-Reliability of the MS Scheme

16. Handoff completion rate Handoff rate Two-Terminal MTTF of the MS Scheme

17. The SM Scheme • Mobile Interoperable Object Reference (MIOR) • The LOCATION_FORWARD message

18. Expected-Reliability of the SM Scheme

19. Two-Terminal MTTF of the MS Scheme

20. Time-Dependent Reliability Importance • It measures the contribution of component-reliability to the system expected-reliability

21. Reliability-Importance of the SM Scheme

22. The MM Scheme

23. The MM Scheme (cont’d)

24. The MM Scheme (cont’d)

25. General Two-Terminal MTTF • nm MHs and ns SHs • Each MH or SH has the same probability to initiate a communication

26. General Two-Terminal MTTF (cont’d)

27. Conclusions • Define the expected-reliability to embody the mobility characteristic introduced by handoff • Observe: • The failure parameters of MH, AB, and SH behave similarly on the MTTF; however, the failure parameter of HLA takes little effect on the MTTF • If the handoff happens frequently, we should improve the performance of the handoff completion and location forwarding mechanism • The general two-terminal MTTF increases with the number of SHs but decreases with the number of MHs. • Identify the reliability importance of each component with respect to the expected-reliability