Sleep control for energy efficiency in ethernet passive optical networks
View Patent ↗A method sets certain downstream traffic scheduling rules at an optical line terminal OLT and certain sleep control rules at optical network units ONUs. Both downstream traffic scheduling rules and sleep control rules are common information owned by both the OLT and ONUs. The method sets the traffic scheduling rules that each ONU is allocated with some time slots every cycle if the ONU has downstream traffic. Rather than using a control message to notify ONUs with their queue status, the method lets ONUs infer whether its downstream queue is empty or not based on downstream traffic scheduling and lets the OLT infer the status of an ONU based on sleep control rules.
1. A method for controlling downstream scheduling in an Ethernet passive optical network EPON, said method comprising the steps of:
i) setting downstream traffic scheduling rules at an optical line terminal OLT for a plurality of ONUs, comprising:
defining a time duration of 2 ms as a downstream traffic scheduling cycle;
in a scheduling cycle, allocating each ONU with some time duration if it has downstream traffic, wherein ONUs need not be allocated with continuous time durations within a scheduling cycle; and
if said OLT infers that an ONU is sleeping, said OLT queuing the arrival of downstream traffic of the ONU until said ONU wakes up;
ii) transmitting said rules to optical network units ONUs, each ONU owning information of the downstream traffic scheduling rules, such that the ONU infers its current downstream queue status based on historical arrival downstream traffic;
iii) according to the inferred queue status, said ONUs making their own sleep decisions based on selective sleep control rules, said sleep control rules, being implemented at said ONUs, being known by said OLT; and
iv) based on said sleep control rules, said OLT inferring a status of said ONUs, and buffering incoming downstream traffic of sleeping ONUs responsively.
2. The method of claim 1 , wherein said steps i)-iv) cooperatively enable efficiently putting said ONUs into sleep without extending an EPON MAC protocol and not requiring handshaking between said OLT and ONUs.
3. The method of claim 1 , wherein the downstream traffic inference at said ONU in step iii) comprises that if an ONU failed to receive any downstream data traffic within an EPON traffic scheduling cycle, said ONU infers that its downstream queue is empty, whereby, rather than being explicitly notified by OLT about its downstream queue status, said ONU infers its downstream queue status simply by monitoring the downstream bandwidth allocated among ONUs.
4. The method of claim 1 , wherein said sleep control rules comprise that if an ONU does not receive downstream data traffic for x traffic scheduling cycles, said ONU switches into a sleep state and sleeps for y traffic scheduling cycles, said x traffic scheduling cycles being listening cycles, and y traffic scheduling cycles being sleeping cycles, said x and y being known to said OLT such that said OLT can infer a sleep status of said ONUs.
5. The method of claim 1 , wherein said step iv) comprises that to avoid missing said downstream traffic when an ONU is sleeping, said OLT infers the sleep status of said ONU, and then buffer its incoming downstream traffic until said ONU wakes up, to enable the ONU status be inferred by said OLT, said OLT owning information of the sleep control procedure implemented at each ONU.
6. The method of claim 1 , wherein said step iv) comprises:
if said OLT does not allocate any time slots to an ONU for x traffic scheduling cycles, said ONU will enter into sleep status in the next predetermined number of traffic scheduling cycles; and
after an OLT infers that an ONU is sleeping, it buffers the arrival downstream traffic of this ONU until the ONU wakes up from sleep.