Overlap signaling occurs when digits are sent one by one in separate messages.

At this point, the local exchange sends a CALPRC message to TE-A indicating that the call setup started. If TE-B accepts the incoming call, an ALERT message is returned. The local exchange then sends an ALERT to TE-A, and if this is a speech call, a ringing tone is applied to the B channel.

When TE-B answers the call, a CONN message is sent to the exchange where the B channels are connected; a CONN message also is sent to TE-A. The local exchange acknowledges TE-B's CONN with a CONACK; TE-A also can acknowledge the CONN with a CONACK.

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