UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
6-5
COMMUNICATION REDUNDANCY
6-5.1
Typically the only communication redundancy made is between subsystem
field panels and the system head-end. Redundancy between field panels and devices is
cost prohibitive. A common method of achieving communication redundancy is
achieved by running primary as well as backup RS-485 lines. If this is done, it is best to
use different raceway routing schemes.
6-5.2
New product developments and improved design configurations increasingly
harden communication system redundancy. This concept is currently more applicable
to DTM IT (servers and telecommunication links) systems as opposed to vendor-
specific ESS subsystems, such as ACS, CCTV, and IDS. Redundant communication
paths are established such that if a component or link goes down, communication is
maintained through an alternate communication path. While some people refer to these
designs as "self-healing", the term is really a misnomer because the failed component is
still a failed component. Alternate communication paths are employed until the fault can
be corrected.
6-6
TRANSMISSION MODES/PROTOCOLS
6-6.1
Several modes and protocols exist for electronic security data transmission.
These include serial communication (RS-485, RS-232), network communication using
Ethernet or TCP/IP protocol, dial-up modem, T-1 line, and wireless.
6-7
TRANSMISSION MEDIA
6-7.1
Hardwired. Hardwired refers to using dedicated proprietary (DoD-owned)
conductors to transmit data/video between DTM nodes. Dedicated conductors can be
copper or fiber-optic.
6-7.1.1 Copper Conductors. Generally, copper conductors can be run to 750 feet
using standard RG-59/U connectors. Use of RJ-11/U conductors can extend that
distance to 1,500 feet. RJ-6 should be used for longer distances. (A robust design
makes use of RG-6/U, 100% double-shielded cable for outdoor applications.) These
distances are general guidelines. Changes in technology permit longer distances using
repeaters. Disadvantages of copper conductors include susceptibility to electromagnetic
interference, radio-frequency interference and damage from lightning strikes.
6-7.1.2 Fiber Optic. Fiber optic allows transmission over longer distances by using
light, which does not have the higher resistance loss over distance of copper
conductors. Furthermore, fiber optic is not affected by electromagnetic interference or
lightning. The incremental cost of installing a higher quality fiber-optic line is not
significantly more for a 100 Base T line than a 10 Base T line. When in doubt, the
designer should err on the side of the higher quality line. Fiber optic cable comes in two
varieties, single-mode and multi-mode.
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