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 MIL-HDBK-232A
5.4.6.1.1 General. The prime purpose of a PTF is the restoration and
rerouting of circuits. The cardinal rule is continuity of the operations.
The patching must include a provision for every wire on a circuit to be
switched to another circuit. There must be no means of patching directly
from the RED side to the BLACK side, or among different RED compartmented
patches. In order to accomplish this restriction, four schemes may be used:
physical separation, dissimilar patching, dissimilar wiring, and dedicated
switching.
5.4.6.1.1.1 Physical separation. In larger facilities, identical patching
equipment may be used for RED compartmented and noncompartmented digital
signals and BLACK digital signals, provided each group is separated from the
other by a distance greater than the longest available patch cord.
Traditionally, manufacturers have not made cords greater than 6 feet (1.8 m)
in length (see figure 31). The design should not include interbay trunking
between compartmented and noncompartmented bays.
5.4.6.1.1.2 Dissimilar patches. It may not be possible to provide adequate
separation in a facility. In this situation, dissimilar patches should be
used to prevent patching into other communities (see figure 32).
5.4.6.1.1.3 Dissimilar wiring. If physical separation cannot be achieved,
and dissimilar patches cannot be used, then each community should be wired to
the patches in a unique manner. When designing the dissimilar wiring scheme,
the goal is to cause the equipment to become inoperative should a mispatch
occur. For instance, if a clock line and COMSEC control line were reversed,
such as sync-initiate, a mispatch would put the clock on the control line,
causing the COMSEC to continually attempt to resynchronize. Without the
clock, the COMSEC could not operate (see figure 33). If multiple communities
exist in a facility, dissimilar wiring may become too cumbersome to be
practical.
5.4.6.1.1.4 Dedicated switching. Single channel facilities should not use
patches at all, but should use A-B switches and x-switches to swap equipment
(see figures 34 and 35).
5.4.6.1.2 Troubleshooting. Troubleshooting capability in a PTF may be as
simple as plugging test equipment into a line or monitor jack, or as
sophisticated as remote switching of test equipment into a line. Test
equipment may include oscilloscopes, distortion analyzers, data scopes, bit
error ratio testers, and pattern generators. If a switching matrix is used,
separate matrices are required for RED and BLACK. Equipment used to trap and
display data must not be capable of reintroducing that data into a circuit.
If the equipment is to be used for both RED and BLACK testing, positive
controls arc required to prevent crossing RED and BLACK signals. It may be
necessary to certify this equipment using criteria for cryptographic
equipment.
5.4.6.2 Local area networks (LANs). LANs are often described as privately
owned optimized networks, offering reliable high-speed communications
channels connecting information processing systems in limited geographic
areas, such as offices, buildings, building complexes, posts, bases, camps,
and stations with such services as word processing, data processing,
electronic mail, and database management. LANs are becoming used
increasingly because of the highly flexible nature of configurations and
services which can be provided. LANs may be implemented using private
automatic branch exchanges (PABX), broadband coaxial cable systems, and
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