Optimux-106 multiplexers combine four E1 or T1 channels and an optional Ethernet link over a fiber optic uplink. A pair of Optimux units provides a simple and low-cost solution for connectivity over distances of up to 120 km. For transmission reliability, an optional modular second link provides automatic backup upon link failure. An optional second power supply provides power redundancy for failsafe operation. Each of the four signals of the tributary interface is transmitted independently, so that each channel can be set to a different clock source.