Cross amplification occurs when a submarine branching unit (SBU) slips erbium-doped fiber amplifiers (EDFAs) at landing points, between isolators and a combiners, that excite erbium ions, maintaining them in L1 - L2 - L3 states configured to their relative wavelengths. Unlike coaxial amplification, which alters voltage in a continuous modification of electrical current, either prior to an RG-6 or RG-59 on spans managed by the ISP. Depending on where it's stored, coaxial amplification will require anywhere from 12-24 volts.