Adtran 1186002F1 MX2820 M13 MUX Specifications: MX2820 M13 MUX Provides 1-to-1 redundancy Meets the requirements for NEBS Level 3 Plug-in unit for the MX2820 chassis that provides an M13 multiplexer function to the MX2820 system Two MX2820 M13 MUX modules are used together to provide a redundant M13 multiplexer circuit.