system printouts.  The MPD program provides an additional capability for on-line message composition and editing ability, and outgoing message error analysis (before  transmission).  It  also  provides  a  proof  copy with paper tape for off-ship transmission. The (V)2- MPD system consists of the same equipments as the (V)2 system with the addition of MPD units, which are modified video displays. NAVMACS (V)3 The  NAVMACS  (V)3  configuration  automates certain  processing  functions  required  in  the  handling  of narrative messages.  It serves as an afloat terminal within  those  communications  networks  using  broadcast and  point-to-point  modes  of  operation  on  both conventional and satellite transmission paths. The  (V)3 configuration interfaces with up to four channels of fleet broadcast, and up to four channels of full-period  termination  send-and-receive  circuits.  It also interfaces with one channel of incoming and outgoing high-speed satellite link message traffic to and from CUDIXS. The  (V)3  configuration  also  interfaces  with  off-line torn tape and manual transmit/receive circuits of any type. The (V)3 system provides the capability of on- line  message  composition  and  on-line  message  retrieval fom magnetic tape. NAVMACS (V)5/(V)5A The   NAVMACS   (V)5/(V)5A   system   is   an automated communications processing system capable of interfacing a mix of input/output channels. This system  is  enhanced  with  the  addition  of  remote terminals for message input. It includes up to four incoming  broadcast  channels  and  eight  itinerant,  netted, and fully dedicated communication network channels. It  also  includes  one  incoming/outgoing  high-speed satellite  link  with  CUDIXS  and  onboard  peripheral devices. The  (V)5/(V)5A  system  includes  a  remote  terminal capability for direct input/output of narrative and data pattern messages to high-volume  onboard user areas. Remote  terminals  consist  of  a  medium-speed  printer, video  display,  and  paper  tape  reader/punch,  or  a combination   thereof,   depending   on   the   unique requirements of the various remote terminals. COMMON USER DIGITAL INFORMATION EXCHANGE    SYSTEM The Common User Digital Information Exchange System (CUDIXS) provides a bidirectional, ship-to- shore-to-ship, high-speed digital data communications link   between   a   ship   and   a   NCTAMS   or NAVCOMMTELSTA. Subscriber stations use the NAVMACS as their terminal. The link consists of a single  Fleet  Satellite  Communications  (FLTSATCOM) half-duplex  channel.    The  link  is  dedicated  to synchronous    communications  between  the  CUDIXS shore station (Net Control Station (NCS)) and the subscribers  afloat.  Each  CUDIXS  communications  link can operate with up to 60 subscribers. There are two types of subscribers: special and primary. Special subscribers are those ships that are assigned subscriber identification (SID) numbers 1 through 10. Special subscribers can send and receive narrative traffic to and from CUDIXS. Primary subscribers are assigned SID numbers 11 through 60. Primary subscribers are restricted to a send capability only. They can receive their shore-to-ship message traffic via other means, such as the fleet broadcast  or  fill-period  terminations.  Both  types  of subscribers can send or receive operator-to-operator (order wire) messages. CUDIXS/Subscriber Net Cycle CUDIXS/subscriber   communications   are accomplished through a modified round robin network discipline.  The  basic  round  robin  net  operating  concept transfers net control from one subscriber to the next on a prearranged  basis,  completing  one  net  cycle  when  each participating subscriber has transmitted. In the  CUDIXS/subscriber modified round robin operating concept, transmission timing and scheduling are determined solely by the CUDIXS shore station designated the NCS. Each net cycle starts when the NCS transmits a Sequence Order List (SOL) along with narrative  traffic  and  operator-to-operator  messages. The SOL specifies the order in which each subscriber transmits during the next net cycle and the amount of time allocated each transmission slot. Each subscriber, in  turn,  will  transmit  at  a  time  computed  from information in the SOL. A net cycle can range from 20 to 120 seconds, depending upon the amount of transmit time requested by the subscribers and the amount of data transferred. 1-15