The MX2820 STS-1 MUX is a multiplexer unit that plugs into an MX2820 chassis. The MX2820 STS-1 MUX interfaces to a standard STS-1 signal from the network to provide 28 DSX-1 or 21 E1 outputs on the terminal side through the demapping of 28 VT1.5s or 21 VT2s. Two MX2820 MUX cards are used together to provide a redundant STS-1 multiplexer circuit. The MX2820 STS-1 MUX provides 1:1 redundancy and meets the requirements for NEBS Level 3.