This read-write value specifies the exact ABCD signalling bit pattern that represents an on-hook condition for the channel, with the valid range narrowing to 0 through 3 under SF framing or extending to 0 through 15 under ESF/E1-CAS framing, and it only matters when cesChanIdleDetEnable is set to enableOnhookDet. An administrator sets this to match the specific signalling convention used by the connected PBX or voice equipment on CESM-8T1/E1 channels. For example, if the connected equipment signals on-hook differently under ESF framing than under SF framing, this value must be adjusted accordingly when the framing mode changes.