Trunk Supervisory Signaling: Wink-Start

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The following scenario summarizes the wink-start protocol event sequence:

• The calling office seizes the line by activating its M-lead.

• Instead of returning an off-hook acknowledgment immediately, the called switch allocates memory for use as a dial register, in the area of memory it uses to store incoming digits.

• The called switch toggles its M-lead on and off for a specific time (usually 170 to 340 ms). (This on-hook/off-hook/on-hook sequence constitutes the wink.)

• The calling switch receives the wink on its E-lead and forwards the digits to the remote end. DTMF tones are forwarded across the E&M link in the audio path, not on the M-lead.

• The called party answers the telephone, and the called PBX raises its M-lead for the duration of the call.

If the timing of the returned wink is too short or impossible to detect, the trunk uses immediate-start, which the following section describes.