Recommendation U.2
                    STANDARDIZATION OF DIALS AND DIAL PULSE GENERATORS
                         FOR THE INTERNATIONAL TELEX SERVICE
                               (former CCIT Recommendation E.2, 1951;
                             amended at Arnhem, 1953 and Geneva, 1956)
               The CCITT,
         considering
               (a) that, when dials and dial pulse generators are used for the process  of
         automatic selection by subscribers to the  international  telex  network,  it  is
         advantageous to standardize as far as possible the characteristics of such  dials
         and dial pulse generators;
               (b) that the stand               the   dialling   speed   and
         lost     motion     periods     of      dials      presents      no
         technical difficulty;
              (c)   that, for the satisfactory working of certain  automatic
         systems, the time between successive pulse  trains  should  not  be
         less than 500 milliseconds, but that experience has shown that  the
         minimum time taken by an experienced operator to rotate the dial is
         of the order of 300 milliseconds;
              (d)   that pulse ratios from 1.2:1 to 1.9:1  will  ensure  the
         satisfactory working of existing automatic switching systems;
              (e)   that these pulse ratios can be usefully adopted  with  a
         view to simplifying direct calling between subscribers,
         unanimously declares the view
               (1) that in the international telex  service,  when  dials  or  dial  pulse
         generators are used for the automatic selection of subscribers:
               a)  the dialling speed shall be standardized at 10 pulses per second with a 
                  tolerance of ± 10%;
               b)  the lost motion period of dials shall be not less than 200 milliseconds 
                  nominal value;
               c)  the inter-digit pause of dial pulse trains  generated  by  dial  pulse
                  generators shall not be less than 600 milliseconds;
               (2) a)  that the pulse ratio must be between 1.2:1 and 1.9:1, the  nominal
                      ratio may be chosen as lying between 1.5:1 or 1.6:1;
                  b)  that  when  the  selection  signals  pass  through  a  regenerative
                      repeater it may be advantageous to use a nominal ratio of 1.5:1.

































                                                         Fascicle VII.2 - Rec. U.2   PAGE1