Abstract: A telephony switching system for interconnecting a plurality of telephone lines. A port storage circuit dedicates an area to each telephone line for storing status information including supervisory information and dial digit information for the corresponding telephone.A port event processor monitors incoming supervisory information from each port means connected to each telephone line to update the corresponding information in each area of the port storage circuit. Upon the occurrence of predetermined events, such as the receipt of all the digits in a telephone number, the port event processor produces an event code that is also stored in the port storage area. A call processor scans all the port storage areas to establish, for each port means, a progression of call states in response to the event information and other information in the port storage circuit and to update control information in the corresponding area.