Why does Telecom use DC power?

Telecom passes signals of voices. If AC power is used, the voice line will have a disturbance that can disrupt the communication; on the other hand, there is no such limitation in DC power. DC power is not restricted to frequency variation or leading power factor. Also, DC power can be stored; thus, backup for telecom buses can be easily given by batteries directly without any power conversion loss.

 DC power is more energy efficient. It has low capacitance losses and can travel longer distances. The corona discharge and the skin effect do not apply to DC power. It's an active power so the power factor doesn't apply to it.