Recommendation U.31
                                 PREVENTION OF CONNECTION TO FAULTY STATIONS
                                 AND/OR STATION LINES IN THE GENTEX SERVICE
                           (former CCIT Recommendation E.9, Geneva, 1956)
               The CCITT,
         considering
               (a) that correct reception of the answerback code at the beginning and  end
         of a telegram should safeguard the correct transmission of the telegram;
               (b) that it accordingly becomes essential to  provide  adequate  signalling
         for cases when  a  teleprinter  is  temporarily  unable  to  participate  in  the
         international service, on account of paper trouble, faults, etc.;
         unanimously declares the view
               (1) that faults during the transmission of a telegram shall be signalled as
         far as possible by the automatic transmission of a clearing signal;
         recognizing, however,
               that it will be impossible to signal  all  faults  that  may  occur  on  an
         established connection,
         unanimously declares the view
               (2) that it is essential that absence of paper on a  receiving  teleprinter
         should be signalled by the clearing signal; and
               (3) that, since the receiving Administration is responsible for the receipt
         of the telegram when the answerback signals have been correctly exchanged, it  is
         responsible for making the necessary arrangements to ensure security of operation
         (for example, if the tape should break or become jammed);
               (4) that in the case of a faulty station line or teleprinter at the  moment
         of the call, the existing automatic switching networks use one  or  more  of  the
         following signalling conditions : no call-connected signal, busy signal,  service
         code DER or no return of answerback. All these signalling conditions ensure  that
         a telegram is not transmitted over a faulty connection;
               (5) that in the case of a faulty station line out of an office group it  is
         essential that the faulty line should be busied out as  quickly  as  possible  so
         that traffic may be offered automatically to all the other lines in the group.





































                                                        Fascicle VII.2 - Rec. U.31   PAGE1