UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
5-5
SYSTEM CONFIGURATION
5-5.1
Subcomponents of an IDS can be configured in an "AND" or "OR"
configuration. In the "AND" configuration, two or more sensors must detect intrusion for
an alarm notification to occur. In the "OR" configuration, only a single sensor need go
into alarm for a notification to occur. The "AND" configuration is used when a concern
about nuisance alarms exists. The "OR" configuration is more secure and is used to
increase the probability of detection. An example is pairing two microwave sensor fields.
In the "AND" configuration, both Field A and Field B have to be in alarm to cause alarm
notification. In the "OR" configuration, if either Field A or Field B go into alarm, then an
alarm signal is sent to the Dispatch Center. Addressable sensors allow the capability to
switch the "AND/OR" configuration from the Dispatch Center. However for some
facilities, such as SCIFs, this feature should be disabled. Table 5-4 displays the
advantages and disadvantages of each configuration.
Table 5-4. Advantages and Disadvantages of "AND" and "OR" Configurations
Pros
Cons
Decreased
Decreased
AND
probability of
nuisance alarms
detection
Increased
Increased
OR
probability of
nuisance alarms
detection
5-6
IDS DESIGN GUIDANCE
5-6.1
The IDS Designer must first determine the design objectives for the project,
usually expressed as a Probability of Detection (Pd). Some sample requirements are a
Pd of 95% for most assets and a Pd of 99% for critical assets. Understanding the
requirement, the designer can then go about laying out the ESS and strategy. Consider
a case study of having to provide a Pd of 99% for a critical asset. Some sample vendor-
specifications for three types of IDS sensors are shown in Table 5-5.
Table 5-5. Sample Probability of Detection Factors
Product
Probability of Detection
95%
Buried Cable
95%
Fence-Mounted
Fiber Optic
99%
93
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