Expected-Reliability Analysis for Wireless CORBA with Imperfect Components

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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

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Wireless CORBA Architecture
Wired Network
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Outline

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

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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

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Mean Time to Failure (MTTF)

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

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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

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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

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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

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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

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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

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Assumptions (contd)

• The failure parameters for the four components,
  MH, AB, SH, and HLA, are constant, which are ?,
  ?, ?, and ?, respectively
• The MHs sojourn time with an AB and the handoff
  completion time are exponentially distributed
  with parameters ? and ?, respectively

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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)

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The MS Scheme
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The System State Probability
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Expected-Reliability of the MS Scheme
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Two-Terminal MTTF of the MS Scheme
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The SM Scheme

• Mobile Interoperable Object Reference (MIOR)
• The LOCATION_FORWARD message

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Expected-Reliability of the SM Scheme
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Two-Terminal MTTF of the MS Scheme
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Time-Dependent Reliability Importance

• It measures the contribution of
  component-reliability to the system
  expected-reliability

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Reliability-Importance of the SM Scheme
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The MM Scheme
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The MM Scheme (contd)
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The MM Scheme (contd)
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General Two-Terminal MTTF

• nm MHs and ns SHs
• Each MH or SH has the same probability to
  initiate a communication

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General Two-Terminal MTTF (contd)
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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