In general, when an abnormal condition occurs in the setting up of a call, the outgoing operator in semiautomatic operation and the calling subscriber in automatic operation should receive an indication to show that it is necessary to make a new attempt to set up the call or to take other appropriate action.
ITU-T Q.116 SPANISH-1988 history
1988ITU-T Q.116 SPANISH-1988 INDICATION GIVEN TO THE OUTGOING OPERATOR OR CALLING SUBSCRIBER IN CASE OF AN ABNORMAL CONDITION