Advise the connected ASC by routine service message  if  only  one  transmission  can  be accounted  for. An  ASC  receiving  notification  of  a  duplicate transmission should search its records to determine if the message was received in duplicate. If the message was not received in duplicate, it must be traced on a station-to-station  basis  to  determine  the  point  of duplication. Magnetic Tape Messages Magnetic tape is one of the principal media used in electronic  data  processing  equipments  (EDPEs). Magnetic  tape  terminal  stations  (MTTSs)  in  the AUTODIN  provide  for  the  rapid  exchange  of  large volumes of data in a relatively short period of time. The basic mode  of MTTS operation with other AUTODIN tributary stations is either full duplex or on a store-and- forward basis. In the continental United States, terminals that have compatible  equipment  and  circuit  speeds  and  are connected to the same ASC may communicate directly by Hybrid AUTODIN Red Patch Service (HARPS). HARPS provides a direct subscriber-to-subscriber encrypted circuit.  HARPS uses the same circuit and equipment  normally  used  in  the  message-switching component of the network. Communications centers not serviced by HARPS communicate by normal message switching, which automatically performs the necessary speed, format, and code conversions. Operating  Rules All  received  tape  reels  must  be  periodically dismounted  and  made  available  for  delivery  as scheduled by a receiving activity and system manager. A magnetic tape reel accepted by a communications facility for transmission is screened and arranged for transmission  according  to  majority  message precedence levels contained on the reel. Establishment of transmission schedules is the responsibility of the commands concerned. Prior coordination is necessary to provide for efficient use of the equipment and circuit time. Schedules are limited to 30 minutes per period. Most facilities establish their own procedures for maintaining reel accountability and ensuring that message   transmission   has   been   accomplished. Message header and EOT printouts are finished by the message  originator  with  each  reel  of  tape  to  be transmitted. If a message cannot be transmitted, the MTTS operator returns the reel to the originator, identifying the message (or messages) that could not be sent. The originator is also provided the reason for the nontransmission, if known. Terminal equipment should not be used to change message  media  format  for  customer  convenience;  for example,  changing  from  magnetic  tape  to  narrative records. Operating Precautions Communications station master records, such as history tapes and journal records, remain with the communications facility until destroyed. History tapes are labeled to prevent them from being inadvertently delivered to addressees with live traffic tapes. Recorded information is very close to the edge of the tape. Tape-edge indentations, caused by careless tape handling, will seriously affect the accuracy of magnetic tape recordings. You should be aware that tape splices are not permitted in reels of tape used for traffic. Message Formats Message  formats  used  within  the  AUTODIN require  that each message contain a message heading, text,  and  EOT  record.  The  textual  material  on  magnetic tapes may consist of a wide variety of information recorded in either structured or nonstructured formats, depending upon the type of system. EOT is either a single N or four consecutive Ns. The header, text, and EOT cards of magnetic tape messages are always transmitted in the AUTODIN common language code (ASCII). This is accomplished by  automatic  code  conversion  logic  provided  in  the magnetic  tape  terminal. The text of magnetic tape messages can be prepared by the EDPE system in 80-character data images, series record images, or by variable-length record images. The  length  of  data  records  to  be  transmitted  by AUTODIN may vary according to user requirements. For general transmission of data throughout the system, computerized  terminals  must  be  capable  of  transmitting records that contain from 18 to 1,200 characters. Subscribers desiring to transmit messages that contain fewer than 18 or more than 1,200 characters must ensure that the addressee is capable of receiving such  records  prior  to  transmission.  Typical  line  formats of magnetic tape message records are described in JANAP  128. 1-11