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DEMAND-ASSIGNED MULTIPLE ACCESS (DAMA)  SUBSYSTEM

 
  
 
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. 3-15

   


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