CFVCX8 Network 8 Line Exchange UnitCFVCX8 Network 8 Line Exchange Unit A VoCALL Emergency Voice Communications System (EVCS) is a fixed, secure, bi directional, full duplex voice communication system to assist fire fighters in an emergency in high rise buildings or large sites where Radio communication may not work, and covers the operation of both fire telephones and disabled refuge systems. The VoCALL EVCS is designed to fully comply with BS5839 Part 9 (abb. Pt9) for use as a fire