E&M Delay-Start Signaling
Delay-start signaling, as depicted in Figure 2-19, is the original start protocol for E&M.
Figure 2-19. Trunk Supervisory Signaling: Delay-Start
Delay-start is used when all of the equipment is mechanical and requires time to process requests. The following scenario summarizes delay-start signaling:
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When you place a call, your calling switch goes off hook by activating its M-lead.
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The called switch acknowledges the request by activating its M-lead, and then rotates armatures and gears to reset its dial register to zero.
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When the dial register at the called switch is in the ready state, the called switch deactivates its M-lead.
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The calling switch then sends dialed digits. DTMF tones are forwarded across the E&M link in the audio path, not on the M-lead
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When the called party answers, the called switch again activates its M-lead.
Echo
Although a local loop consists of two wires, when it reaches the switch, the connection changes to four wires with a two- to four-wire hybrid converter. Trunks then transport the signal across the network, as shown in Figure 2-20.