摘要:
全球暖化議題逐漸受到重視的現在，不論在傳統的被動光接取網路或長距離被動光接取網路中，能源節省都被視為一個重要的問題。將被動光接取網路中閒置的光網路元件裝置切換至睡眠模式以節省能源被視為一個可行的方案，許多研究遂根據此提出許多睡眠排程機制。這些機制根據其排程的特性可被區分為sleep for more than cycle機制與sleep within one cycle機制。而在此篇論文中，我們主要是針對sleep within one cycle機制提出改善的方法。
Sleep within one cycle機制則會在每一個週期至少會傳送一個GATE訊息給每一個光網路元件，此GATE訊息中除了有給光網路元件(ONU)的傳輸時槽外尚會有通知其下次醒來時間點的資訊。而下次醒來的時間點則取決於光線路終端(OLT)下次發送GATE訊息給此光網路元件的時間點。然而在當下發送GATE訊息的時間點，光線路終端未必能決定下次發送給此光網路元件的時間點。在先前文獻中所提的方法Sleep Mode Awareness (SMA)是利用預測的方式來找出此時間點。但由於預測誤差值所造成光網路元件early wake-up現象會產生額外能源消耗，且此額外能耗會隨者系統負載與來回通訊延遲時間的增加而上升。為此，我們提出一個可以讓光網路元件early wake-up現象消失的睡眠排程機制Single GATE Sleep Scheduling (SGS)，但此機制會將光網路元件的睡眠時間分成二段，並產生一段固定的額外能耗。由於此固定能耗在低系統負載或來回通訊延遲低的情況可能會大於SMA中預測誤差所造成的額外能耗，為了使系統的額外能耗可以最小化，我們將SGS與SMA整合後提出了一個Hybrid-SGS-SMA睡眠排程機制。透過比較固定額外能耗與預測誤差所造成的額外能耗，Hybrid-SGS-SMA機制可以動態選擇SMA或SGS作為其睡眠排程機制，使得系統的額外能耗可以保持最小化。模擬結果顯示了Hybrid-SGS-SMA機制可以無縫的在二種睡眠排程機制間切換，因此可以藉由額外能耗最小化使得系統耗能最小化。

Abstract –Energy saving is an essential issue in passive optical networks (PONs) due to the increased concerns for global warming. Among the various energy saving techniques in PONs, putting the idle optical network unit (ONU) into sleep mode to conserve power is considered as a promising approach. Therefore, many sleep mode scheduling mechanisms have been proposed based on the ONU sleep mode. The previously proposed mechanisms can be broadly classified as either "sleep for more than one cycle" mechanisms or "sleep within one cycle" mechanisms. The two categories mainly differ in their scheduling policies. In this thesis, we mainly focus on improving "sleep within one cycle mechanisms".
In "sleep within one cycle" mechanisms, the OLT would poll (i.e., transmit a GATE message) each ONU in every cycle where the GATE message contains information to the ONU, including the transmission window and the next wake-up time. The next wake-up time is determined by the next polling time. In fact, the OLT may not be able to determine the next polling time at the current polling time. In previous studies, Sleep Mode Awareness (SMA) uses a prediction method to find the time epoch. However, prediction error may induce ONU early wake-up and result in an extra power consumption which decreases the power-saving efficiency of the system. Furthermore, the extra power consumption will increase when the system load and the round trip time (RTT) increase. We propose a sleep scheduling mechanisms named Single GATE Sleep Scheduling (SGS) which can avoid the ONU early wake-up problem by splitting one sleep period into two sleep periods, but it will cause a fixed extra power consumption due to extra mode switching overhead. To minimize the extra power consumption of the system, we develop an effective scheduling method of combining our proposed method with SMA, called Hybrid-SGS-SMA mechanism. By comparing the fixed extra power consumption with extra power consumption caused by prediction error, Hybrid-SGS-SMA can dynamically select sleep scheduling mechanism according to the current environment. The simulation results show that Hybrid-SGS-SMA can directly switch between different sleep scheduling mechanisms without reconfiguration overhead and thus minimizing the power consumption of the system.

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