Expected-Reliability Analysis for Wireless CORBA with Imperfect Components Chen Xinyu

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

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

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

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

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

7 Why Expected-Reliability Terminal mobility introduces handoff Terminal mobility introduces handoff Handoff causes the change of number and type of engaged communication components, then results in different system states 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 Two-terminal expected-reliability at time t Q s (t) Q s (t) the probability of the system in state s at time tthe probability of the system in state s at time t R s (t) R s (t) the reliability of the system in state s at time tthe reliability of the system in state s at time t Mean Time to Failure Mean Time to Failure

9 Assumptions There will always be a reliable path in the wired network There will always be a reliable path in the wired network The wireless link failure is negligible The wireless link failure is negligible All the four components, AB, MS, SH, and HLA, of wireless CORBA are failure-prone and fail independently 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 R s (t) R s (t) n(s) – the number of engaged components in system state s n(s) – the number of engaged components in system state s R i (t) – the reliability of the i th component R i (t) – the reliability of the i th component c – the type of a component c – the type of a component mh, ab, sh, or hlamh, ab, sh, or hla k c (s) – the number of component c in state s k c (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 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 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) Static Host to Static Host (SS) a traditional communication scheme a traditional communication scheme Mobile Host to Static Host (MS) Mobile Host to Static Host (MS) Static Host to Mobile Host (SM) Static Host to Mobile Host (SM) Mobile Host to Mobile Host (MM) Mobile Host to Mobile Host (MM)

13 The MS Scheme

14 The System State Probability

15 Expected-Reliability of the MS Scheme

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

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

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 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 n m MHs and n s SHs n m MHs and n s SHs Each MH or SH has the same probability to initiate a communication 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 Define the expected-reliability to embody the mobility characteristic introduced by handoff Observe: 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 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 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. 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 Identify the reliability importance of each component with respect to the expected-reliability