隨著網路的迅速發展Voice over IP(VoIP)、Video on Demand(VoD)和Internet Protocol Television(IPTV)等各種低延遲、高頻寬需求的網路服務相繼出現，在接取網路(Access Network)上需要的能源也日益增加。因此目前接取網路的方案中乙太被動光接取網路(Ethernet PON, EPON)的能源節約是目前接取網路的重要議題。許多文獻提出睡眠模式排程機制考慮每個ONU單一服務類別的平均延遲限制，但在網路上同時存在多種服務的情況下，考慮延遲限制較嚴格的類別造成節能效果較差，考慮延遲限制較寬鬆的類別造成延遲限制較嚴格的類別無法滿足其延遲限制。
本論文提出的方法根據目前一個ONU的上傳或下傳是否有封包在確定的時間會違反其類別的延遲限制，在長時間的睡眠(Deep Sleep)和短時間的睡眠(Cyclic Sleep)兩個機制做切換。在各類封包還有一段時間才違反延遲限制狀況下OLT會讓ONU進入Deep Sleep機制之下的睡眠模式讓ONU有更多機會進入睡眠模式。並以兩階段(Two-stage)佇列控制各類封包的延遲，將快要違反延遲限制的封包移動到兩階段中的第二階段，在第二階段佇列有封包時ONU才回到Acitve，可在考慮分類別延遲限制的前提下盡可能延長ONU停留在睡眠模式的機會。在模擬結果中顯示比起只考慮延遲限制較嚴格類別的方法，提出的方法可以在較高網路負載(network load)的狀況下進入睡眠模式同時保持延遲限制，並且因停留在睡眠模式的時間增加而可以節省更多能源。

With the rapid growth of the Internet, web services like Voice over IP (VoIP), Video on Demand (VoD), Internet Protocol Television (IPTV) which requires low-latency and broadband network are arising. Therefore, energy consumption of network infrastructures like Access Network is dramatically increasing. The issue about saving energy on access network like Ethernet PON (EPON) and Gigabit-capable PON is considered a well-known problem. Many research proposed sleep mechanisms that concerned about single class’s delay constraint. While there are multiple classes of service exist on the network transmission, saving energy with high-priority class considered is less efficient, and high-priority class’s delay constraint won’t be satisfied while saving energy with low-priority class considered.
The proposed scheme switch between Deep Sleep mechanism and Cyclic Sleep mechanism according to the number of packets which are going to violate their class’s delay constraint in a certain time. If an ONU has packets which are going to violate their delay constraint, the OLT commands ONU to enter sleep mode by using Cyclic Sleep mechanism while the ONU is not transmitting packets. If an ONU has no packet which are going to violate delay constraint in a certain time, the OLT commands the ONU to switch to Deep Sleep mechanism to sleep as long as it can. The probability of entering sleep mode under Deep Sleep increases while the proposed scheme let ONU enter sleep mode while there are packet in ONU’s upstream or downstream queue. The probability of exiting sleep mode under Deep Sleep decreases while the ONU decides to start transition from sleep to active mode if there are packets going to violate it’s delay constraint in a certain time. The simulation result shows the ONU of proposed scheme is able to enter sleep mode under higher network load and ensure the delay performances under the delay constraints while the previous schemes that only considered high-priority delay constraints could not. The proposed scheme is saving more energy while the ONUs stay in sleep mode for longer time.

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