Abstract: To provide a high bit rate link between telecommunication network users, HDSL modems are installed on the user premises and at corresponding subscriber line termination units in an exchange. The modems in the exchange are connected to access units of the exchange which include networks of add and drop multiplexers interconnected in a ring and connected to a drop port. It is shown that it is a simple matter to organize dynamic switching between users connected to the same access unit or neighboring access units in the same exchange. Other calls are routed to other exchanges.