Transcript Network Management 1 - Eastern Illinois University

School of Business
Eastern Illinois University
Network Management 1
(Week 16, Tuesday 12/5/2006)
© Abdou Illia, Fall 2006
Learning Objectives

Generating Useful Statistics
–
–

Availability
Reliability
Centralized Network Management
2
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?
3
Availability
4

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
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
5
Availability
A(t) = a/(a+b) + b/(a+b) x e-(a+b)t
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
Q: What will be the availability of the modem if the Approximation equation is used?
Availability

7
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 threemonth period using the Approximation method.
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
8
Reliability

Reliability: probability that a component or system
will be operational for the duration of a transaction
time t.

Reliability is function of:
–
–
9
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
Reliability
11
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