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Understanding Network Management: Statistics, Availability, and Reliability

This document outlines the essential concepts in network management focusing on generating useful statistics, availability, and reliability of network components. Key learning objectives include understanding the importance of statistics in identifying network issues, calculating availability using mean time between failures (MTBF) and mean time to repair (MTTR), and assessing reliability through statistical equations. Examples provide practical insights, demonstrating how to apply statistical methods to measure the performance of network devices effectively.

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Understanding Network Management: Statistics, Availability, and Reliability

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  1. School of Business Eastern Illinois University Network Management 1 (Week 16, Tuesday 12/5/2006) © Abdou Illia, Fall 2006

  2. Learning Objectives • Generating Useful Statistics • Availability • Reliability • Centralized Network Management

  3. Generating Useful Statistics • Statistics: Data about network operation or network devices operation • Example: Availability of a modem, Reliability of a Hub, transmission speed, etc. • Statistics are very helpful for network management • Could help identifying problems in Network operation • Could be used to demonstrate the need to invest in technology Q: What kind of tools, already introduced in class, can be used to generate useful statistics?

  4. Availability • Availability: probability that a particular component or system will be available during a fixed time period • Availability is function of: • Mean time between failures (Given by manufacturer or generated based on past performance) • Mean time to repair (Found in studies or in our archives) • Mean time between failures (MTBF) is the average time a device or system will operate before it fails. • Mean time to repair (MTTR) is the average time necessary to repair a failure

  5. Availability • Standard equation: • A(t) = a/(a+b) + b/(a+b) x e-(a+b)t • in which: a = 1/MTTR • b = 1/MTBF • e = natural log function • t = the time interval • Approximation equation: • Availability% = (Total available time – Downtime)/Total available time

  6. A(t) = a/(a+b) + b/(a+b) x e-(a+b)t Availability Suppose we want to calculate the availability of a modem that has a MTBF of 3000 hours and a MTTR of 1 hour. The availability of this modem for an 8-hour period is: a = 1/1 b = 1/3000 = 0.00033 A(8 hours) =1/(1 + 0.00033) + 0.00033/(1 + 0.00033) x e-(1 + 0.00033)8 = 0.9997 + 0.00033 x 0.000335 = 0.9997 Q: What will be the availability of the modem if the Approximation equation is used?

  7. Availability • A component has been operating continuously for three months. During that time, it has failed twice, resulting in downtime of 4.5 hours. Calculate the availability of the component during that three-month period using the Approximation method.

  8. Availability • To calculate the availability of a system of components: • Calculate the availability of each component • Find the product of all availabilities • Example: If a network has tree devices with availabilities of 0.992, 0.894, and 0.999, the availability of the network is: 0.992 x 0.894 x 0.999 = 0.886

  9. Reliability • Reliability: probability that a component or system will be operational for the duration of a transaction time t. • Reliability is function of: • Mean time between failures • Transaction time • Mean time between failures (MTBF) is the average time a device or system will operate before it fails. • Transaction time is the time interval of operation to complete a given transaction.

  10. Reliability • Reliability is defined by the equation: • R(t) = e-bt • in which: b = 1/MTBF • t = the time interval of the operation

  11. Reliability What is the reliability of a modem if the MTBF is 3000 hours and a transaction takes 20 minutes, or 1/3 of an hour (0.333 hours): R(t) = e-bt b = 1/MTBF = 1/3000 t = 0.333 R(0.333 hours) = e -(1/3000)(0.333) = e -0.000111 = 0.99989 Q: If a component has a MTBF of 500 hours and a transaction takes 4 seconds, calculate the reliability of the component

  12. Summary Questions See slides # 6, 7, 11

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