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 MIL-HDBK-232A
2.
System configuration: The system configuration must effectively isolate
the station equipment from all lines which leave the PCZ.
2.1
Two separate dedicated wiring frames (or sets of wiring frames) are
are maintained inside the PCZ containing the CBX to support
connections with facilities outside that PCZ. These are termed
"external" wiring frames (in this paragraph) to distinguish them
from frames used to connect the CBX to equipment located within the
PCZ. One of the "external" frames is used to terminate all lines
entering from outside the PCZ (C.O. trunks, tie trunks, telephone,
etc.). It is located at the point of entry for these lines and is
available for inspection. The second of the "external" frames
provides the connections to the CBX. Cross-connections between the
two "external" frames are limited to only those needed to extend
active central-office lines to the CBX. The "external" wiring
frames are separated by at least three feet from each other and from
all internal wiring frames. No cross-connections are permitted
between internal and "external" frames. CBX port circuit packs
connected to "external" wiring frames are not installed in the
same circuit carriers as those connected to Internal wiring frames.
No two carriers share common cabling to the wiring frames. All
cross-connect strapping pairs at the cross-connect fields are
labeled as to identification and/or purpose. Each cross-connect
label cites the appropriate paragraph or drawing of the installation
document which prescribes the connection.
2.2
Each individual subscriber station has dedicated running wires to a
specific, individual, port circuit of the CBX. Off-hook connections
between port circuits are accomplished by metallic (or electronic)
switching or by multiplex bus methods. The CBX keeps the running
wires of every port circuit separate and unconnected from those of
every other port except in the case of metallic switching, and then
connections may only occur for ports actually engaged in an
information interchange between off-hook subscriber stations (or
between a station and a trunk). Audio coupling in either direction
through a switch or between a port circuit and a multiplex bus only
occurs when the associated station equipment or trunk is off-hook.
(Off-hook here is intended to mean that a subscriber station or
trunk connected to the CBX is initiating or actively engaged in
communication either with the CBX itself or with some other
subscriber station or trunk by means of a link established by the
CBX.)
2.3
No port circuits or assigned station directory numbers are shared by
extension stations inside the PCZ with extensions outside the PCZ.
All extensions from the same port circuit or with the same station
directory number are either wholly contained within the PCZ or
wholly excluded from it.
2.4
Speakerphones are not permitted.
3.
Prohibited functions: Some operational features that may be available
with the CBX involve functions which are not consistent with good audio
security practices. These functions are expressly prohibited and any CBX
feature using them must be disabled.
3.1
The CBX must not be able to place or hold any subscriber station in
an off-hook condition unless directed to do so by that subscriber
station itself. The off-hook condition is completely controlled by
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