A call control signal transmitted by the called data circuit-terminating equipment ( DCE ) to the calling data terminal equipment ( DTE ) to report (a) the progress of a call by using a positive call progress signal or (b) the reason why a connection could not be established by using a negative call progress signal.
CALL PROGRESS SIGNAL
Meaning of CALL PROGRESS SIGNAL in English
Telecommunication standard terms English vocab. Английский словарь стандартных телекоммуникационных терминов. 2012