ADSL2 Low Power Modes

We have often made the point that the majority of energy savings opportunities in consumer electronics low power modes will only be realized when communications standards start to include power use as a criteria. Power use is a significant part of standards for portable equipment due to the high value of longer battery life and smaller products, but until now I have not seen much interest in standards that effect mains powered equipment.

I recently found that the standard for the next version of ADSL (Asymmetric Digital Subscriber Line) includes some very prominent low power modes. As outlined in a white paper on ADSL2, first generation ADSL transceivers stay in full power mode regardless of whether they are transmitting or not. The new standard specifies two low power modes (L2 and L3) which use substantially less power. L2 mode is designed as an intermediate mode which the device can cycle in and out of at a rate that depends on the data transfer speed. The device can enter and exit L2 mode instantly without any service interruption or bit errors. L3 mode is a full sleep mode for when there is no data traffic and transition to the more active modes can take as long as three seconds.

In addition to the energy benefits of lower power consumption and reduced heat buildup in telco cabinets, the low power modes reduce cross talk and noise, resulting in more reliable connections.

It seems that most other communicating consumer devices such as set-top boxes and modems should be able to use similar low power mode transitions to reduce power use, if only standards are written to take advantage of them.