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live video on a specific, or set of screens. The duration of the recording may vary and may be configured
for a specific amount of time, or until the alarm condition is cleared by the SOC staff. This enables the SOC
staff to assess the situation and more accurately determine the course of action. Video is often displayed on
one of the PACS clients or in some smaller deployments on the PACS Server monitor.
In sites where assessment speed is essential, fixed position cameras are preferred in that they are always
assumed to be pointed in the right direction and cover the intended area. However, pan, tilt and zoom (PTZ)
cameras are able to cover a wider area and are often used to supplement fixed cameras. Video control units
that are integrated with PACS, or other IDS equipment, are usually capable of automatically positioning
one, or a group of PTZ cameras to cover and focus on the area from where the alarm signal originated.
Depending on the starting position, cameras may be repositioned and focused to provide a view of the
violated area within a few seconds after a camera control unit receives a command from the PACS or IDS.
As an adversary often moves very quickly and since there are several system processes that must be initiated
before the required video images are actually displayed in the SOC, there is a risk that the camera is
activated a few seconds too late and the video only shows the scene after the adversary is gone. To mitigate
this risk, many modern video systems are capable of displaying video captured a few seconds prior to the
initial event that activated the sensor. This is referred to as pre-alarm recording and the amount of pre-alarm
video is often a customer configurable parameter.
The recorded video is should be time-stamped, associated with a specific event (instance) and stored in a
video log located in a specific storage location and accessed by authorized staff for future viewing, (play-
It is crucial that all system components are synchronized to one authoritative time stamp entity. This may
be a network-centric clock, or a connection to the NIST atomic clock to name two examples. Policies
determine both where and the amount of time these stored video clips are maintained as well as how they
are destructed. These policy decisions guide the process of calculating how much storage space is required.
Number of bits per image, images per second, number of cameras and idle recording rate are parameters
that determine the amount of storage space that is required per hour. [Refer: Section 6: Video Surveillance
Systems for further details.])
If integrated accordingly, a PACS system operator may use a PACS client to request viewing (play-back)
of a previously recorded video clip and maybe even copy selected video recordings from the video system
to the PACS for ease of viewing and analysis. Recorded and stored video is usually locked and cannot be
edited. However, video clips may be copied.
Many video systems are capable of detecting events, which may be categorized and configured in the video
system as alarm events. As an example, consider an attempt to disable a camera that covers an area where
an adversary may not want to be recorded. An attempt to simply disconnect the camera may be detected
and the event triggers an alarm message that is sent to the PACS as a tamper alarm and be annunciated as
per policies that are programmed into the system.
Some of the earlier analog video systems monitored synchronization pulses and video gain signals to detect
interruptions, or sudden changes in the video signals from a camera to video control unit such as a switcher.
These types of signal changes usually result of attempts to replace a camera with another video source that
may be used to inject desired video images into the system, a “man in the middle” type of attack. However,
an inherent characteristic of this approach is that a sudden change of light in the covered area caused a rapid
change in the gain signal and often triggered a video alarm.
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