Recommendation U.70
                                          TELEX SERVICE SIGNALS FOR
                            TELEX TO TELETEX INTERWORKING
                                    (Malaga-Torremolinos, 1984)
               The CCITT,
         considering
               (a) that a basic interworking on international connections will  be  at  50
         bauds using an international telex network and that any telex subscriber can call
         conversion facilities in various countries;
               (b) that Recommendation F.201 specifies:
               -   that a validation of a  called  Teletex  terminal  is  mandatory.  The
                  validation is performed either by a direct validation call or by a data
                  base access;
               -   that if a message delivery to a Teletex terminal fails in the case  of
                  interworking  with  two-stage  selection  procedure,   the   conversion
                  facility should send a non-delivery notification to a telex terminal;
               (c)  that  Recommendation   S.90   specifies   Teletex   requirements   for
         interworking with the telex service and Recommendations  S.62  and  S.70  specify
         control procedures and  a  network-independent  basic  transport  service  for  a
         Teletex;
               (d) that Recommendation X.96 specifies call progress signals  in  a  public
         data network,
         unanimously declares the following view
         1      Scope
               This Recommendation defines service signals which are to be  sent  back  to
         the telex terminal in the event of unsuccessful  validation  for  called  Teletex
         terminal addresses, and service signals of  the  last  delivery  attempt  to  the
         Teletex terminal which are to be  sent  to  the  telex  terminal  as  a  part  of
         non-delivery notification.
                                                TABLE 1/U.70

         MONTAGE: REPRENDRE ORIGINAUX DU LIVRE ROUGE.
         PAS DE NOUVELLE SAISIE = MAINTENU LIVRE ROUGE
         2      Principles
               The following principles should be taken into consideration:
         2.1    Call progress signals arriving from the Teletex network will be  converted
         without changing their original meaning as far as possible.
         2.2    A faulty condition between the Teletex network and the conversion facility
         will be regarded as a faulty condition within the network.
         2.3    A faulty condition between the Teletex network and  the  Teletex  terminal
         will be regarded as a fault of the terminal.
         3      Telex service signals
               1n general, telex service signals specified in Recommendation  F.60  should
         be used. However, the telex service signals listed below  will  be  used  in  the
         following circumstances:
         3.1    1f the format of the Teletex address part is incorrect, the service signal
         NP will be returned.
         3.2    1f the direct validation call is  unsuccessful,  the  conversion  facility
         will transmit the  service  signals  specified  in  Table  1/U.70  to  the  telex
         terminal.
         3.3    If the validation by data base  access  is  unsuccessful,  the  conversion
         facility will transmit the service signals specified in Table 2/U.70.
         3.4    If the message delivery to  the  Teletex  terminal  is  unsuccessful,  the
         conversion facility will transmit  the  service  signals  of  the  last  delivery
         attempt  which  are  specified  in  Table  1/U.70,  as  a  part  of  non-delivery
         notification to the telex terminal.
                                                TABLE 2/U.70
                       Service signals for unsuccessful validation by data base access
                   Abnormal conditions              Service signal
          Unsuccessful results                            NP
                      Note - In addition to the case "the number does not  exist",
                      other cases, for example, "the number is  being  temporarily
                      prohibited" or "the  number  is  out  of  order",  might  be
                      considered as abnormal conditions. But at this  moment  such
                      conditions and the service signals corresponding to them are
                      for further study.





                                                        Fascicle VII.2 - Rec. U.70   PAGE1






































































         PAGE2   Fascicle VII.2 - Rec. U.70