Ground Start Signaling - Ground-start signaling for a two-way dial system is an old technology (introduced in the 1920s). It is used typically on two-way PBX central office trunks with direct outward dialing (DOD) and attendant-handled incoming call service. The ground-start line conductors transmit common battery-loop supervision, DTMF address signalling or loop dial pulses, alerting signals, and voiceband electrical energy.