A system for and a method of providing a telephony service is disclosed. Supplying power to a node in a telecommunications network from a subscriber's premises conflicts with the plain old telephone service POTS. Until the advent of the present invention it was thought that supplying power in this way required either an additional electrical transmission wire or providing voice support within a digital subscriber line (DSL) service. In the proposed system telephony control signals, as supplied by an exchange (103) on to a first section (107) of an electrical transmission line, are converted into modified downstream control signals having a different frequency to electrical power, which is supplied onto a second section (109) of the electrical transmission line, and electrical equipment in a node that interconnects the first and second sections can draw electrical power supplied by the power supply without affecting the operation of a telephone (101).