In a passive optical network, network availability as well as network security will become increasingly important. Traffic- transparent energy-autarkic supervision units located at demarcation points between network segments (so-called demarcation devices, DD) would fill this need. The DD respond to a low-duty cycle low-bitrate control signal which the operator's central office (CO) superimposes to the optical data stream sent to the subscribers. Most of the time the DD stay in a low-energy sleep mode, but awake during very short time intervals for communicating with the CO. In sleep mode, synchronism with the CO is lost. Our new low-energy medium-access control (LE-MAC) protocol assures a fixed "rendezvous" time where all DD can individually respond to the CO. In a small network we show the feasibility of the concept and the functionality of the LE-MAC protocol. The mean current consumption of a DD is less than 1 μA corresponding to 3 μW. With a single inexpensive lithium ion battery, such a DD could operate for more than 10 years.
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