I/O devices use coded languages. These languages are: ASCII Code  —American  Standard  Code  for Information Interchange, eight-level paper tape; and ITA  #2  Code  —American   version   of international TTY alphabet, five-level paper tape. Message Header Programming At the beginning of each AUTODIN message is a header (format line 2) containing pertinent information on the destination of the message. The originator can address a message either to a single addressee or to multiple  addresses.  This  system  saves  time  and requires fewer communications facilities, since only one message is prepared by the originator and sent to the switching  center. The  timing  system  contained  in  AUTODIN equipment briefly connects a switching center to each subscriber terminal in turn. Computer memories act as reservoirs for the incoming messages of each subscriber terminal.  The  computer  is  programmed  to  connect  each terminal in turn during a cycle. Messages received in their entirety are scheduled for output to the addressees’ charnels as their turns arrive in the cycle. AUTODIN has built-in safeguards that can detect almost  any  type  of  hardware  or  format  error. Additionally, a complete (reference) copy of all relayed messages is kept on AUTODIN computer tape. A separate (journal) copy is made of only the addressee(s). Using this journal copy as an index enables the system to locate the reference copy of any message. AUTODIN Tape Messages The AUTODIN system is programmed to accept properly cut tapes and route them through the various switching  centers  and  terminals  en  route  to  their ultimate destination. The system is then able to produce a tape and hardcopy for the designated addressee(s). When preparing a message tape for the AUTODIN system,  you  must  adhere  to  certain  tape-cutting procedures. For example, format lines 1, 2, and 4 must not deviate; otherwise, the ASC will reject the message. The next paragraphs discuss the most important points on proper preparation of tape messages for transmission in the AUTODIN system. ROUTING   INDICATORS.   —Within  the AUTODIN network, a message tape is routed through the AUTODIN system to the addressee(s) by a routing indicator. Routing indicators are combinations of not less than four nor more than seven letters. A routing indicator begins with the letter R or Q. The letter R indicates that the routing indicator is part of the  worldwide  tape  relay  system.  The  letter  Q  indicates that  the  routing  indicator  is  within  a  self-contained network within a command or theater. The  second  letter  of  the  routing  indicator  identifies the  nation  or  international  alliance  to  which  the indicator belongs. For example, the letter U refers to the United  States.  Therefore,  RU  indicates  that  the message tape is part of the worldwide network and is destined to a station in the United States. The third letter of the routing indicator identifies the geographical area in which a particular station is located or from which it is served. This is necessary for relay purposes because the second letter may indicate a large nation within which there are a number of subdivisions or stations. For example, many stations in the United States are designated by the third letter C. Therefore, the first three letters of “RUC” indicate that the tape is part of the worldwide network, destined for the United States, and to a certain geographical area within the United  States. The fourth and subsequent letters of a routing indicator designate relay and tributary stations within the tape relay network. Like the first three letters, the fourth and subsequent letters may vary, depending upon location, area, and other factors. TRANSMISSION   IDENTIFICATION (FORMAT LINE 1). —As a means of maintaining traffic continuity, TTY terminals (modes II, IV, and V) must prefix each message header with a message transmission identification (TI). The ASC validates the elements in the TI. Modes I and III do not require format line 1. The TI is constructed without spaces and must be accurately prepared without corrections. For example, a correctly prepared TI might appear as follows: VZCZCJTA (FIGS) 123 (LTRS) (2CR 1LF) The elements of the TI and their meanings are as follows: l V  —Ensures  that  the  first  character  of intelligence is not lost or garbled; l    ZCZ  —Indicates the start of the message; 1-6