The 16COIU Card supports 16 analog loop start CO lines. The card has a Mode Switch (for taking the card out of service), a status LED indicating proper card operation, and a port activity LED that indicates traffic on the card. Each 16COIU Card also provides two power failure cut-through circuits. When commercial AC power fails, the Card automatically cuts through two line circuits to two power failure single line telephones.

The 8COIU Card supports 8 analog loop start CO lines. The card has a Mode Switch (for taking the card out of service), a status LED indicating proper card operation, and a port activity LED that indicates traffic on the card. Each 8COIU Card also provides two power failure cut-through circuits. When commercial AC power fails, the card automatically cuts through two line circuits to two power failure single line telephones.