This adapter serves as a port doubler for structured twisted pair cabling. As only two wire pairs are used for a 10/100Mbit LAN connection and for an ISDN line, but an RJ45 port in the socket is usually used with all 4 wire pairs, this adapter can be used for so-called ‘cable sharing’. This allows 2 network cables to be combined into one. With a further adapter, the signals at the other end of the double-used cable are distributed to two ports again.