Lesson 2/Learning Event 5
(a) User-to-user circuits (category 1). User-to-user circuits is
a type of service where the end instruments are directly connected through
the DCS, point-to-point circuits. This category has four types of service,
voice, facsimile, telegraph and data.
(b) Voice Frequency Carrier Telegraph (VFCT) Systems (category 2).
Category 2 only has one type circuit/service, which is the VFCT.
(c) AUTOVON access lines (category 3).
This category has three
types of circuits/services which is voice grade or special grade that is
used to access AUTODIN switches.
(d) AUTOVON trunks (category 4).
Category 4 services are
interswitching trunk circuits, voice grade or special grade used between
automatic switches by category 3 users. They may be transoceanic circuits.
(e) AUTODIN access lines (category 5). AUTODIN access lines is a
digital service used to access the DCS. They range from 75 baud DC keying
lines to 4800 b/s. The 2400 b/s through 4800 b/s are used to access AUTODIN
interswitching trunks.
(f) AUTODIN interswitching trunks (category 6).
Interswitching
trunks are a special grade digital, dedicated circuit between automatic
switches. They are used by the 2400 b/s through 4800 b/s users of category
5.
(g) AUTOSEVOCOM access lines (category 7).
This category of
service is normally a 4-wire circuit, used to access the DCS and automatic
switches.
They are used between the secure voice terminal equipment and
technical control facility.
(h) AUTOSEVOCOM trunks (category 8).
This category normally
services 2400 b/s or 50 kb/s secure voice, and may be a point-to-point or
routed through automatic switching networks.
(i) Basic groups, 60-108 kHz (category 9). This category normally
supports user-supplied Frequency Division Multiplex (FDM) of 60-108 kHz at
group level between facilities (unconditioned).
It also supports a
conditioned 50 kb/s requirement between DCS facilities with the use of
Government Furnished Equipment (GFE), data modems and data auxiliary sets,
etc.
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