HDSL's maximum reach is set according to its highest rate, even if the customer does not use full bandwidth. This makes the service available to many more customers. At the same time, in an era when home fax machines are becoming no less essential than refrigerators or microwaves, an additional fax line is also required. However, its two B channels are insufficient to support Fast Internet and more than one voice channel. In order to support voice connectivity when there is a power failure, bypass circuits or remote power feeding for the user equipment are required.
Additional bandwidth is used for management purposes.
Transmission over the single pair requires echo cancellation and adaptive equalizers in order to achieve the maximum range at a specific rate. For each user rate, the modem changes the 2B1Q transmission rate, employing different filters and equalizer settings. The modem's adaptive setting is determined during its initial use, and continues constantly during operation. Meanwhile, business customers are racing to find more and higher bandwidth to support changing needs as their businesses expand. ADSL introduces a delay that is not tolerable for video or voice transmission.