A transmission system includes a transmission path from a transmitting station to a receiving station for both voice telephone service occupying the frequency spectrum below a predetermined frequency f.sub.1 and for data service occupying the frequency spectrum above another predetermined frequency f.sub.3, where f.sub.3 is substantially higher than f.sub.1, a plurality of telephone sets at said receiving station connected in parallel with one another to the transmission path, and where each of the telephone sets has an on-hook state which presents a substantially infinite resistance to the transmission path and an off-hook state which presents a predetermined resistance R to the transmission path. A plurality of separate and substantially identical multi-pole low-pass filters are provided for connection between the transmission path and respective ones of the telephone sets, where each of the low-pass filters has a -3 dB frequency f.sub.2 which lies between f.sub.1 and f.sub.3, and a characteristic impedance of substantially (n*R), where n is a number equal to at least 2.4, thereby reducing the effect of low impedances that develop at frequencies below f.sub.1 because of resonances that occur between f.sub.1 and f.sub.2 with at least one but less than all of said telephone sets off-hook.