Home' RTCA Documents for Review : DO-230H FRAC Contents 79
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report generation. High traffic areas may need additional memory to provide for an extended
Field Control Panels (FCP) should have transaction and alarm buffers of sufficient capacity to store
transactions during a communication failure as per local site-security policy with respect to the airports
capability for corrective maintenance. High traffic areas may require additional memory at the controller to
provide for an extended communication failure.
A PACS server “timeout” is user defined to determine the amount of network latency that is allowed before
the server generates a “Panel Off-line” alarm. When this alarm occurs, the server triggers an automated
process to re-establish communication to the panel. This may be through the same communication line or
in some cases a secondary, alternate communication path.
At the field panel side, a similar timer is configured to determine the amount of network inactivity is allowed
before the panel should react and generate a local notification.
The FCP should provide primary communication over the required cable plant installed for the local facility.
This may be four-wire or two-wire copper lines, coaxial cable, LAN or WAN network cables, or fiber optic
cables, and more recently, wireless networks. In case of primary communication line failure, a FCP should
have the capability of communicating with the host computer or server using a secondary communications
mode suitable for the local environment.
Another method of providing a backup communication path for the controller is to provide redundant
cabling for alternative path communications (if the field controller supports the configuration).
Spread Spectrum Communication
Spread spectrum is a form of wireless communications which may be used to communicate with panels in
which the frequency of the transmitted signal is deliberately varied. (For full details, refer Section 9.)
A conventional wireless signal has a frequency, usually specified in megahertz (MHz) or gigahertz
gigahertz), that does not change. For example, when one listens to an FM station at 101.1 MHz on an FM
receiver, the signal stays at 101.1 MHz - it does not go up to 105.1 MHz or down to 99.1 MHz. The digits
on the radio’s frequency dial stay the same at all times. The frequency of a conventional wireless signal is
kept as constant as possible so the signal can be easily located by someone who wants to listen or receive
There are at least two problems when conventional wireless communications are used in security
applications. First, a signal whose frequency is constant is subject to simple jamming and “Man-in-the-
middle” attack techniques. Simply transmitting another signal on, or very near, the frequency of the desired
target frequency will either jam, or a substitute message may be injected. This may be accidental, as in
amateur-radio communications, or it can be deliberate as an adversary attempting hostile action against a
desired target such as an airport. Second, a constant-frequency signal is easy to intercept, and is therefore
not well suited to applications in which information must be kept confidential between the source
(transmitting party) and destination (receiving party).
To minimize troubles that can arise from the above mentioned vulnerabilities of conventional
communications circuits, the frequency of the transmitted signal can be deliberately varied over a
comparatively large segment of the electromagnetic radiation spectrum. This variation is done according to
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