Recommendation U.22
               SIGNALS INDICATING DELAY IN TRANSMISSION ON CALLS SET UP
                           BY MEANS OF SYNCHRONOUS SYSTEMS
                    WITH AUTOMATIC ERROR CORRECTION BY REPETITION
                             (New Delhi, 1960; amended at Geneva, 1964)
               The CCITT,
         considering
               (a) that traffic observations on radio telex channels have shown  that  the
         possible delay in the reception of text transmitted by one subscriber to  another
         is a drawback from the operating point of  view.  The  delay  may  be  caused  by
         repetitions and/or difference in the modulation rate of the teleprinters (traffic
         from Europe to the USA). In case of such delays a subscriber  is  left  in  doubt
         whether he simply has to await transmission of his message over the radio path or
         whether the delay is due to the tardy answering of his correspondent,  for  which
         he will have to pay. Furthermore, in the case of delays due  to  long  repetition
         periods a receiving subscriber may be tempted to answer prematurely, which causes
         garbling of the text;
               (b) that to a certain extent this drawback can be offset by the application
         of a strict operating  procedure  (+?  signal  to  invite  the  correspondent  to
         transmit). However, supplementary technical measures have proved to be desirable;
               (c) that a good technical solution of this problem is to  use  combinations
         No. 32 as a delay signal in the following manner:
               i)  combinations No. 32 are returned to the transmitting subscriber at the
                  rate of one every 5 seconds if he stops transmission during an interval
                  of 10 seconds and the local storage device still contains untransmitted
                  tape;
               ii) combinations No. 32 are sent to a subscriber at the rate of one  every
                  1.2  seconds  if  transmission  is  delayed  by  repetitions   whenever
                  condition i) does not apply;
               (d) that the slow delay  signals  inform  a  sending  subscriber  that  his
         message has not yet been received by his correspondent. The rapid  delay  signals
         inform a receiving subscriber that the received message is not yet  complete  and
         that he should not cut in;
               (e) that in the case of cypher  messages  where  combinations  No.  32  may
         result from the coding procedure, delay signals should not be used. Also  in  the
         case of full duplex working, waiting signals cannot be used. Furthermore,  it  is
         desirab            transmit    waiting    signals    during     the
         setting-up of semi- or fully-automatic  calls,  since  interpolated
         waiting  signals  would  complicate  the  discrimination   of   the
         selection signals and the call-connected  signals.  Therefore,  the
         best solution seems to be to put the switching on and  off  of  the
         delay signal facility under the control of  the  subscribers:  four
         consecutive combinations No. 8 or No. 14 could  be  used  for  this
         purpose;
              (f)    that  the  transmission  of  these  delay  signals  can
         obviously not  be  imposed  on  an  Administration  that  makes  an
         international connection by a landline and radio channel,
         unanimously declares the view
               (1) That, when the Administrations concerned agree that it is necessary  to
         signal to telex subscribers about a delay in transmission over  the  radio  telex
         channel, delay signals shall be used having the following characteristics:
               i)  combinations No. 32 at the rate of one every 5 seconds, returned to  a
                  sending subscriber when he has stopped transmission for a period of  10
                  seconds and if there is still text stored;
               ii) combinations No. 32 at the rate of one every 1.2  seconds  sent  to  a
                  subscriber whenever transmission over the radio channel is  delayed  by
                  repetitions and condition i) above does not apply.
               (2) Sending of combinations No. 32 is cut off as  soon  as  the  subscriber
         starts to transmit again.
               (3) No delay signal will  be  transmitted  while  the  call  is  being  put
         through.








                                                        Fascicle VII.2 - Rec. U.22   PAGE1

               (4) The calling and also the called subscribers can suppress sending of the
         waiting signal at the  two  ends  of  the  radio  circuit  by  transmitting  four
         successive combinations No. 8. The waiting signal can also be started  off  again
         by transmitting four successive combinations No. 14.
               (5) The delay  signal  should  be  switched  off  upon  reception  of  four
         consecutive combinations No. 19 (signal for transfer to data) for the duration of
         the call.
               Note - Administrations must take precautions to ensure that  the  reception
         of combinations No. 32 should not cause spacing of the paper on page-printing  or
         tape-printing apparatus.



























































         PAGE2   Fascicle VII.2 - Rec. U.22