1Network Management 1School of BusinessEastern Illinois University © Abdou Illia, spring 2004(Week 15, Monday 4/19/2004)2Learning Objectives Generating Useful Statistics– Availability– Reliability Centralized Network Management3Generating 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 technologyQ: What kind of tools, already introduced in class, can be used to generate useful statistics?24Availability 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 failure5 Standard equation:A(t) = a/(a+b) + b/(a+b) x e-(a+b)tin which: a = 1/MTTRb = 1/MTBFe = natural log functiont = the time interval Approximation equation:Availability% = (Total available time – Downtime)/Total available timeAvailability6Suppose 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 = 1/1b = 1/3000 = 0.00033A(8 hours) =1/(1 + 0.00033) + 0.00033/(1 + 0.00033) x e-(1 + 0.00033)8= 0.9997 + 0.00033 x 0.000335= 0.9997AvailabilityQ: What will be the availability of the modem if the Approximation equation is used?A(t) = a/(a+b) + b/(a+b) x e-(a+b)t37Availability 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.8Availability 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 = 0.8869Reliability 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.410ReliabilityReliability is defined by the equation:R(t) = e-btin which: b = 1/MTBFt = the time interval of the operation11ReliabilityWhat 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-btb = 1/MTBF = 1/3000t = 0.333R(0.333 hours) = e -(1/3000)(0.333)= e -0.000111= 0.99989Q: If a component has a MTBF of 500 hours and a transaction takes 4 seconds, calculate the reliability of the component 12Summary QuestionsSee slides # 6, 7,
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