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Expected Reliability Analysis for Wireless CORBA with Imperfect Components

This paper explores the expected reliability of Wireless CORBA systems influenced by imperfect components, focusing on the impact of handoff mechanisms as mobile hosts change connections between access bridges. The analysis includes a review of different communication schemes: static-to-static, mobile-to-static, static-to-mobile, and mobile-to-mobile hosts. Key metrics, such as the Mean Time to Failure (MTTF) for various component states and the importance of each component's reliability, are discussed. The conclusions emphasize the need for improving handoff performance to enhance overall system reliability.

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Expected Reliability Analysis for Wireless CORBA with Imperfect Components

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  1. Expected-Reliability Analysis for Wireless CORBA with Imperfect Components Chen Xinyu 2004-02-16

  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

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