A signal , sent in the backward direction, to indicate that a call cannot be completed because the called line is not in a ready condition, but is under control, as opposed to not being in a ready condition and not under control.
CONTROLLED NOT READY SIGNAL
Meaning of CONTROLLED NOT READY SIGNAL in English
Telecommunication standard terms English vocab. Английский словарь стандартных телекоммуникационных терминов. 2012