E&M Immediate-Start Signaling

E&M Immediate-Start Signaling

Immediate-start signaling occurs occasionally if a PBX vendor implements wink-start, shown in Figure 2-18, but does not conform to the standards.

Figure 2-18. Trunk Supervisory Signaling: Immediate-Start

[View full size image]

The following scenario summarizes the sequence of events for the immediate-start protocol:

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

• Instead of receiving an acknowledgment, the calling PBX waits a predetermined period (a minimum of 150 ms) and forwards the digits blindly. DTMF tones are forwarded across the E&M link in the audio path, not on the M-lead.

• The called PBX acknowledges the calling PBX only after the called party answers the call by raising its M-lead.