achieved by a polling and controlled access protocol
installed in the TADIXS radio controller (shore)
software and the TADIXS satellite link controller
(afloat) software.
In the non-DAMA mode, OTCIXS operates in a
half-duplex manner at a data rate of 2400 bps using a
dedicated uhf channel. When functioning in the
DAMA mode, OTCIXS operates at a data rate of 1200
or 2400 bps in a permanently assigned time slot of a uhf
DAMA channel. Control of message traffic
transmission is achieved by a demand-assigned access
protocol installed in the OTCIXS radio controller
(shore) and satellite link controller (afloat) software.
Message Traffic Reception
Each subscriber in the TADIXS network has a
unique identification number recognized by the
subscriber processor. This number serves as the initial
basis for incoming message traffic screening.
TADIXS or OTCIXS satellite link controllers (on
afloat units) compare redundant receptions for
accuracy and form the most accurate composite of the
traffic received.
For surface ship and submarine users, screened
message traffic is sent to the teletypewriter or TDP
system, as applicable. The rest of the traffic is
discarded. The reception of traffic does not make the
satellite link controller send an acknowledgement.
This allows afloat platforms to receive traffic while
operating in an emission control (EMCON) en-
vironment.
DEMAND-ASSIGNED MULTIPLE ACCESS
(DAMA) SUBSYSTEM
The uhf DAMA subsystem was developed to
multiplex several baseband systems or users on one
25-kHz satellite channel. This had the effect of adding
more satellite circuits per channel to the uhf Satellite
Communications System. Without uhf DAMA, each
satellite communications subsystem requires a
separate satellite channel.
DAMA equipment accepts encrypted data streams
from independent baseband sources and combines
them into one continuous serial output data stream.
DAMA interfaces the Navy uhf SATCOM subsystems
and the AN/WSC-5(V) and DAMA-compatible
AN/WSC-3(V) transceivers. The DAMA unit (TD-
1271B/U multiplexer) includes a modem, eliminating
the need to use a separate modem at the AN/WSC-5(V)
or the modem within the AN/WSC-3(V). The
baseband equipment input or output (I/O) data rate
with DAMA equipment can be 75, 300, 600, 1200,
2400, 4800, or 16,000 bps. The DAMA transmission
rate on the satellite link (burst rate) can be 2400,9600,
19,200, or 32,000 symbols per second (sps).
CUDIXS/NAVMACS, Secure Voice, and OTCIXS
currently use 2400 bps. TACINTEL operates at 2400
or 4800 bps, depending upon the ocean area.
The DAMA multiplexed data stream is divided into
frames, with each frame being 1,386 seconds long. Each
frame is subdivided into time slots as shown in figure
3-11. Most of the DAMA frame formats are derived
from this basic format. In the following paragraphs, we
will name and describe the purpose of each slot.
Channel Control Order Wire (CCOW) Slot
This slot is used to transmit system timing and
control information from the channel controller to
subscriber units only. It provides subscriber units with
system timing, configuration, and satellite rf control
information. It occurs at the beginning of each frame.
Return Channel Control Order Wire
(RCCOW) Slot
This time slot provides limited order wire
capability for DAMA-related subscriber-to-channel
controller communications. It is used for transmission
from the subscriber to the channel controller.
Ranging Time Slot
This is the time slot during which the user’s
TD-1271B/U determines the range between the user
terminal and the satellite to set the transmitter syn-
chronization required for timing. All DAMA multi-
plexer transmit times are referenced to the satellite.
Link Test Slot
The link test slot is used to evaluate the
performance of the satellite link. Each subscriber is
able to transmit a fixed data stream through the
satellite, receive that bit stream, and then perform error
analysis automatically.
Figure 3-11.—Basic DAMA frame format.
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