下一代被動光接取網路的能源節約是目前接取網路的重要議題。睡眠模式被認為在被動光接取網路環境是一個可行且有效的節能方案，許多文獻遂提出許多睡眠模式排程機制，透過睡眠模式排程機制適當地分配頻寬與睡眠模式區間。然而這些文獻僅考慮平均延遲時間限制，若直接以平均延遲時間限制作為最大延遲時間限制，會造成超過最大延遲時間限制的封包比例過大，如此對延遲敏感的封包而言會有很大的影響。
本論文提出的方法根據封包的最大延遲時間限制計算並設定睡眠時間，大幅降低超過最大延遲時間限制的封包所佔的比例。此外，本論文提出的方法採用Grant-Before-Report (GBR)方式分配頻寬，GBR方式代表OLT無需事先接收報告，即可授予ONU傳輸封包的頻寬，在相同延遲限制設定下GBR可以比傳統的Grant-After-Report (GAR)方法有較長的周期時間。較長的周期時間意味著模式切換的頻率減少且睡眠時間也可以較長，因此可以達到較低的能源消耗。模擬結果顯示本論文提出的方法比起其它方法，不僅可維持良好的節能效率，而且可以確保各類別封包延遲皆小於其各自的最大延遲時間限制，即使在網路負載為0.9時仍僅不到0.76%(遠低於其它方法的11.35%至51.79%)的封包延遲無法滿足最大延遲時間限制。

Energy saving in the next-generation passive optical networks (NG-PONs) is an essential issue. The sleep mode is considered as a feasible and efficient solution for energy saving in NG-PONs. Therefore, many researchers have proposed some sleep mode scheduling schemes to schedule data transmission and sleep period appropriately. However, these schemes only considered the average delay constraint for the delay-sensitive frames. It is possible that the average frame delay is satisfied, but the maximum frame delay is exceptionally large and deviated from the average delay greatly. This will result in an adverse effect on the delay sensitive frames.
The proposed energy efficient dynamic bandwidth allocation (EEDBA) scheme is based on the maximum-delay-constraint of the delay-sensitive frames to derive the appropriate sleep period and it can significantly reduce the percentage of unqualified frames. Moreover, the EEDBA method follows Grant-Before-Report (GBR) fashion rather than the conventional Grant-After-Report (GAR). GBR (GAR) fashion means the transmission time slots for an incoming frame will be granted without (with) reporting in advance. Given the same maximum-delay constraint, GBR-based methods can result in the longer cycle time than GAR-based ones. Thus, the transition frequency between active mode and sleep mode is reduced and the length of sleep length can be longer accordingly. Hence the energy consumption of the proposed scheme is lower than the previous schemes. The simulation result shows that compared to other schemes, the proposed EEDBA scheme in NG-PONs can achieve low power consumption while obeying the maximum-delay constraint of the delay-sensitive frames. Even when the traffic load rises up to 0.9, the percentage of unqualified frames is still less than 0.76% which is significantly lower than 11.35%-51.73% in other schemes.

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