# Reduce Functions

A reduce function aggregates the operational status for the BS. The alarm severity from the edges are used as input for the reduce function. For this operation the following reduce functions are available:

Table 1. Status calculation Reduce Functions
Name Description

`Highest Severity`

Uses the value of the highest severity, weight is ignored.

`Threshold`

Uses the highest severity found more often than the given threshold, e.g., 0.26 can also be seen as 26%, which means at least 2 of 4 alarms need to be raised to change the BS.

`Highest Severity Above`

Uses the highest severity greater than the given threshold severity.

`Exponential Propagation`

This reduce function computes the sum of the given child severities based on a base number. For this computation the severities are mapped to numbers:

WARNING=0, MINOR=1, MAJOR=2, CRITICAL=3

All other severities are ignored.

For the aggregation the following formula will be used to compute the resulting Business Service severity from its n child entities based on the base number b:

severity = |__log_{b}( sum_(i=1)^n b^(ch\ildSeverity_{i}) )__|

In summary the base value defines how many items of a severity x will result in a severity x+1. Results lower as 0 are treated as NORMAL and results higher than 3 are treated as CRITICAL. If all input values are of severity INDETERMINATE, the result is INDETERMINATE.

For example if the Business Service depends on four child entities with the severities WARNING, WARNING, NORMAL and NORMAL and the base defined by the number 2 the following computation will be made:

severity = |__log_{2}( 2^{0} + 2^{0} + 0 + 0 )__| = |__log_{2}( 1 + 1 + 0 + 0)__| = |__log_{2}( 2 )__| = |__1__| = 1

which corresponds to the severity MINOR. The same computation with the base value of 3 results in:

severity = |__log_{3}( 3^{0} + 3^{0} + 0 + 0 )__| = |__log_{3}( 1 + 1 + 0 + 0)__| = |__log_{3}( 2 )__| = |__0.63__| = 0

which means WARNING.

The following table shows the status calculation with Edges assigned to an IP Service. The IP-Service is driven by the monitoring of the ICMP service for three Web Server. In the table below you find a configuration where Web Server 3 is weighted 3 times higher than the other and a threshold of 0.33 (33%) is configured.

Table 2. Example for status calculation using the Threshold function
Name Weight Weight Factor Input Severity Operational Status Critical Major Minor Warning Normal

Web-ICMP-1

1

0.2

Critical

Critical

0.2

0.2

0.2

0.2

0.2

Web-ICMP-2

1

0.2

Normal

Normal

0

0

0

0

0.2

Web-ICMP-3

3

0.6

Warning

Warning

0

0

0

0.6

0.6

Total

1.0

0.2

0.2

0.2

0.8

1

Percentage

100%

20%

20%

20%

80%

100%

The Operational Status Severity is evaluated from left to right, the first value higher then the configured Threshold is used. In this case the Operational Status is set to Warning because the first threshold which exceeds 33% is Warning with 80%.