(Common Channel Interoffice Signaling) The signaling technique used in the public switched telephone network that transmits voice conversations and control signals over separate networks. Voice conversations are handled by the traditional telephone switches, while control signals are transmitted over a packet-switched network, providing faster connects and disconnects and allowing data, such as calling number, to be included. CCIS messages can inform switches of network congestion and outages. Previous to CCIS, control signals travelled with the voice (in-band). See AIN and SS7. See also CCS.