An energy efficient cyclic sleep control framework for ITU PONs

Cyclic Sleep Mode (CSM) is a widely studied and standard energy conservation technique for Passive Optical Networks (PONs). The energy savings provided by CSM increase with longer Asleep and shorter SleepAware state periods. However, this also leads to increased communication delays. Moreover, too short SleepAware time may degrade dynamic bandwidth assignment (DBA) performance and even may cause delay of urgent PLOAM messages from OLT. Neither CSM standards nor existing studies provide any detailed framework to configure CSM performance and control parameters in accordance to the target delays. Another limitation of existing studies is their assumption of a single traffic class during sleep mode analysis. They do not consider the impact of CSM on Type-1 (T1) to Type-4 (T4) traffic classes defined by International Telecommunication Union (ITU). Most of these studies also neglect the role of DBA by considering a fixed bandwidth assignment. However, upstream delays critically depend on the DBA performance and its impact should not be ignored during CSM studies. Therefore, this study presents an Efficient Cyclic Sleep (ECS) framework to configure all CSM parameters and timers with optimum values in the presence of all traffic classes and DBA scheme. The proposed scheme maximizes the energy savings even at very high traffic loads while satisfying the target average delay limit of 56 ms for both US and DS links. A sleep buffer approach is used to configure the Local Wake Up Indication (LWI) events and all CSM control timers at the OLT and ONU. The proposed scheme is compared with two other reported schemes. Simulation results show up to 84.1% energy savings at very low traffic loads and 43% savings at 80% network traffic load (equal to traffic arrival rate of 550Mbps per ONU). The delay variance results for both US and DS also remain under 1 ms.