The MX2820 MUX cards are capable of combining independent T1s, E1s, or T1s and E1s on the same DS3. Each pair of MUX cards provides built-in 1: 1 redundancy on the DS1 and DS3 signals. Advanced diagnostics include CSU loopbacks, NIU loopbacks, C-bit loopbacks, and built-in BERT (Bit Error Rate Testing) capabilities.