An apparatus for use in an all digital loop contains a first network node (30), a second network node (31), and a data transmission line (32) there between. Each one of the first and second network nodes (30, 31) is operable to transmit to the other at least one digitised telephone signal with other digital data via a set of carriers. One of the first and second network nodes (30, 31) thereto includes or is associated with means which in the event of power failure at the first network node (30), is operable selectively to provide power to the first node (30) such that the first node (30) operates only via a limited subset of said carriers. This limited subset is such as to minimise the power required for the transmission of a telephone lifeline signal between the first and second nodes (30, 31).