American Audio VELOCITY - REV 4-05 Betriebsanleitung PDF herunterladen (Seite 124)

METRO RAIL DESIGN CRITERIA SECTION 9 / SYSTEMS

DE304.09 9-119 Revision 4 : 05/09/12

Metro Baseline Re-Baseline: 04/29/10

In order to digitally sign a file, all data/video file, which is to be protected, should

passed through hashing function. The hashing function should produce a large

checksum value for the file, which should be then encrypted using the private

key.

The two most recognized and acceptable by Metro hashing functions could used

for digital signature technologies are MD5 and SHA-1.

The American Bar Association (Digital Signature Guidelines:

http://www.abanet.org/scitech/ec/isc) describes digital signatures as using public

key cryptography and a 'hash function' derived from the message itself. The

hash function is an algorithm created from enough of the message data to

ensure that it could only be created from those data. The message and the hash

function are then encrypted with the sender's private encryption key to make a

digital signature which is unique. The receiver decodes the message with a

related version of the encryption key previously given to the intended recipient

by the sender (or held by a trusted third party). The message is verified by

computing the hash function again and comparing it with the original.

Watermarks cannot be used for traceability of video evidence.

9.9.4 Triggers/Video Analytics (Analytical Video Systems – AVS)

In some situations, systems may include triggers that lead to the recording of

images at a variable rate, or in a sequence, that differs from the normal operating

mode. An example of this would be to change from a low resolution recording mode

to real-time mode when triggered by an alarm button. (15FPs to 30FPs or better).

Another example would be to create an alert from an otherwise unmonitored camera

if motion was detected in the field-of-view of that camera using AVS.

Test recordings should be made to ensure that activation of the triggers, trip wires or

other AVS based alarms and subsequent operation of the incident recorder, does

not have an adverse effect on the quality of the recorded images and meets a

minimum playback resolution of horizontal resolution stated in the section 9.8.2A.

Video Analytics (VA), or Analytical Video Systems (AVS), are increasingly being

used within Metro to aid operators and controllers. Where numerous screens are

used within an ROC, VA systems aid operators to direct their attention at areas of

interest depending on how and what type of VA is employed.

Passive Infrared detectors can be added to a systems network and tied to individual

or groups of cameras that can be brought to the attention of an operator when

triggered. There are manual triggers and automatic triggers. The manual triggers

initiated by AVS generally more reliable although much simpler in operation as they

are fed back to the ROC separately on the network and then “paired” with a group of

cameras at the ROC. AVS, or software based VA, is increasingly becoming more

advanced for detecting abnormal behavior as well as triggering events based on

intrusion. Automatic VA systems are usually housed at the ROC on separate

servers having camera feeds directed into them. Software based analysis is then

performed on these feeds and alerts generated. Metro will define what features to

detect or monitor based on the project specific. Metro will ensure that these can be

“measured” and “tested” in some way to ensure that false alarm rates are kept to a

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