These may serve either interoffice trunks or, using Integrated Subscriber Loop Carrier, subscriber lines. This system is known as Common Channel Interoffice Signaling. Common Channel Interoffice Signaling (CCIS) in a separate channel not accessible to the caller. By placing a call to a non-local toll-free number, interoffice trunks were used for free. "Common Channel Interoffice Signaling" (CCIS) systems. The local tournament usually includes competitors from various organizations, referred to as the interoffice competition.