Recommendation U.5
                              REQUIREMENTS TO BE MET BY REGENERATIVE REPEATERS 
                                        IN INTERNATIONAL CONNECTIONS
                           (former CCIT Recommendation E.5, Geneva, 1956;
                   amended at Geneva, 1964, Mar del Plata, 1968 and Geneva, 1976)
               The CCITT,
         considering
               (a)  that  it  may  be  desirable  to  include  regenerative  repeaters  in
         teleprinter switching networks;
               (b) that the only signals other  than  teleprinter  signals  that  must  be
         transmitted  by  a  regenerative  repeater  are  the  clearing  signal  and   the
         call-connected signal (see S  3.1.3  below),  since  all  other  signals  can  be
         bypassed;
               (c) that other signals may be transmitted by regenerative repeaters,
         unanimously declares the view
         1      that, when regenerative repeaters  are  used  in  switching  systems,  the
         clearing signal should be retransmitted with a minimum of delay. This delay is of
         course the same as for the transmission of teleprinter signals;
         2      that to ensure the correct retransmission  of  the  call-connected  signal
                  (see S 3.1.3 below) and the clearing signal, the regenerative repeater must not automatically insert the stop element in 
         either of these signals;
         3     that for other signals that  may  pass  through  regenerative
         repeaters, the tolerances at the origin  and  after  retransmission
         through the regenerative repeaters are as stated below.
               Note - The characteristics and tolerances quoted are  for  the  signals  at
         the origin. The tolerances at the input to the regenerative repeater will  depend
         on the degree of distortion in the transmission path from the origin to the input
         of the regenerative repeater. The tolerances at the output  will  depend  on  the
         normal tolerances for the regenerative repeater.
         3.1    Pulse signals
         3.1.1  Call-confirmati n   (proceed-to-select)   signal.   Type   B
               signalling
               A pulse of stop polarity of duration from  17.5  to  35  milliseconds.  The
         nominal duration of the  pulse  after  retransmission  through  the  regenerative
         repeater should not be less than 20 milliseconds or more than 40 milliseconds.
               Note - This signal will be transmitted over only  one  international  trunk
         circuit and should thus normally pass through  not  more  than  one  regenerative
         repeater.
         3.1.2  Dial selection signals. Type B signalling
               These signals have been standardized (Recommendation U.2) at a  dial  speed
         of 10 pulses per second ±  10%,  and  a  pulse  ratio  (start/stop)  between  the
         tolerance of 1.2:1 and 1.9:1 with a nominal ratio lying between 1.5:1 and  1.6:1.
         Such signals after retransmission through several regenerative  repeaters  should
         not fall outside the tolerances stated above.
         3.1.3  Call-connected signal. Type A signalling
               A pulse of start polarity  lasting  150  ±  11  milliseconds.  The  nominal
         duration of the pulse after retransmission through several regenerative repeaters
         should be within the limits of 140 to 160 milliseconds.
         3.1.4  Busy signal. Type B signalling
               Pulses  of  stop  polarity  lasting  165-260  milliseconds,  separated   by
         intervals of start polarity lasting  1.5  seconds  ±  30%.  After  retransmission
         through several regenerative repeaters  neither  the  pulses  nor  the  intervals
         should be shortened by more than 10%.
         3.2    Sequence signals (involving a single change of polarity)
         3.2.1  Calling signal. Types A and B signalling
         3.2.2 Call-connected signal. Type B signalling
               These signals (inversion from  start  to  stop  polarity)  have  no  timing
         tolerances as such. It is, however, essential that they should  be  retransmitted
         by a regenerative repeater with a minimum of delay which in no case should exceed
         20 milliseconds.








                                                         Fascicle VII.2 - Rec. U.5   PAGE1