The SP4 Telephone Zone Controller (SP4-TZC) controls the zone paging capability of the SAFEPATH??4 Multi-Function Facility Communications System. It is used in conjunction with the SP40 and the SP4-APS (SP4 Addressable Paging Splitter). Audio Boosters SPB-80/4, SPB-160, and SPB-320 can be used in conjunction with the SP40. Each audio booster can use additional SP4-APS splitters, increasing the number of possible paging zones.