Cutting back on energy consumption has become a priority for most service providers as an effective
means of reducing operating costs while minimizing environmental impact, particularly in
terms of greenhouse gas emissions. Power savings in the access network, however, cannot come at
the expense of lifeline services such as voice — these must be sustained for as long as possible using
battery backups when electrical service is interrupted. Both next-generation EPON and GPON
include full-service and sleep modes to accommodate these power demands. A third potential mode
would allow the optical network unit (ONU) to economize on backup battery power consumption
during a power outage.