Abstract: An automatic call distribution (ACD) switching system having a plurality of agent/trunk interface circuits for selectively connecting a plurality of telephone trunks to a plurality of agent workstations. The ACD switching system includes at least a first line interface module having a shelf control module for controlling a plurality of carrier card slots. At least one of the carrier card slots includes a carrier card for supporting a plurality of agent/trunk interface circuit "subcards" in closely-aligned parallel relation to the carrier card. Each carrier card and the shelf control module include digital processing circuits and an HDLC transceiver to facilitate the interconnection of first and second agent/trunk interface circuits upon a call processing request for service. In the preferred embodiment, control information used to effect the interconnection of the agent/trunk interface circuits is transmitted throughout the switching system in a dedicated timeslot along a digital voice PCM bus.