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

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

3. 3 Generating Useful Statistics n Statistics: Data about network operation or network devices operation n Example: Availability of a modem, Reliability of a Hub, transmission speed, etc. n 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. 4 Availability n Availability: probability that a particular component or system will be available during a fixed time period n 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) n Mean time between failures (MTBF) is the average time a device or system will operate before it fails. n Mean time to repair (MTTR) is the average time necessary to repair a failure

5. 5  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 Availability

6. 6 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 Availability Q: 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)t

7. 7 Availability n 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. 8 Availability n To calculate the availability of a system of components: – Calculate the availability of each component – Find the product of all availabilities n 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. 9 Reliability n Reliability: probability that a component or system will be operational for the duration of a transaction time t. n Reliability is function of: – Mean time between failures – Transaction time n Mean time between failures (MTBF) is the average time a device or system will operate before it fails. n Transaction time is the time interval of operation to complete a given transaction.

10. 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. 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. 12 Summary Questions See slides # 6, 7, 11