在被動乙太光纖網路(Ethernet passive optical network, EPON)上未使用溝槽剩餘頻寬(Unused slot remainder, USR)是一個影響效能的重要議題。未使用溝槽剩餘頻寬是由於OLT分配的上傳頻寬因乙太封包的不可切割性，造成ONU上傳封包時，仍有不足以上傳一個封包的剩餘上傳頻寬，這些剩餘頻寬，因為無法被其他ONU使用，導致頻寬利用度下降及封包延遲上升的問題。針對未使用溝槽剩餘頻寬，目前文獻提出可使OLT分配頻寬必定可被ONU完整使用的改善方法來消除未使用溝槽剩餘頻寬。依照ONU使用REPORT訊息的方式，這些方法可分為Single queue report(SQR)與Multiple Queue Reports(MQR)兩種機制。
SQR機制為ONU僅使用REPORT訊息內一個Queue Report欄位記錄需求頻寬上傳給OLT，此需求頻寬一般是根據最大可上傳頻寬的大小來決定，有可能會導致OLT只能分配Queue Report欄位所記錄的需求頻寬，無法分配多餘的頻寬，來提升頻寬利用度。MQR機制則是ONU使用REPORT訊息內多個Queue Report欄位來紀錄不同的需求頻寬上傳給OLT。MQR機制無法只使用最大可上傳頻寬的大小來決定多個Queue Report欄位的紀錄值，而改用門檻值與門檻差值來決定每個Queue Report欄位所記錄的需求頻寬，使得OLT進行頻寬分配時，可選擇所記錄的需求頻寬較大的Queue Report欄位。但是因為無法決定最佳的門檻值與門檻差值，MQR機制仍會導致OLT無法分配多餘的頻寬，來提升頻寬利用度。因此，不同於找尋最佳的門檻值與門檻差值，本論文提出一個基於交錯式預測演算法預測OLT分配頻寬進而配置多個佇列回報(Queue Report)欄位內容的Active scheduling with predictive queue report(ASPQR)演算法。模擬結果顯示ASPQR演算法相較於MQR機制可讓ONU獲得更多的上傳頻寬，降低平均封包延遲，並且進一步降低封包遺失率，其封包遺失率改善幅度相對於SQR機制可達50%。

The Unused Slot Remainder (USR) problem is an important issue for network performance in the Ethernet Passive Optical Network (EPON). Due to the inseparability of an ethernet packet, if the size of a remainder is insufficient to transmit any packet in the corresponding ONU’s (Optical Network Unit’s) buffer, neither the ONU nor other ONUs in the EPON system can use the remainder to transmit any packet. The USR problem is seen as a waste of bandwidth that will decrease the bandwidth utilization and indirectly increase packet delay. Many previous works have proposed bandwidth allocation schemes to prevent the USR problem. According to the usage of a queue report field in the REPORT message, these proposed schemes can be classified into two categories: a single queue report (SQR) and a multiple queue report (MQR).
In the SQR scheme category, the ONU uses a single queue report field to record the required bandwidth. The required bandwidth is decided according to the maximum transmission window. The network utilization can’t promote because the allocated bandwidth is limited by the size of the maximum transmission window. On the other hand, an ONU uses a multiple queue report field in a single REPORT message to record the required bandwidth in the MQR scheme category. To decide the value of each queue report, an MQR scheme adopts a threshold and a threshold difference. After the OLT (Optical Line Terminal) performs a DBA (Dynamic bandwidth allocation) computation, it will choose a required bandwidth that is as large as possible and grant the corresponding bandwidth to each ONU. However, the actual grant bandwidth is unequal to the optimal grant bandwidth. Thus, the bandwidth utilization still can be improved. To improve the usage of the queue report, we propose an interleave predictive algorithm-based active scheduling with a predictive queue report algorithm (ASPQR) to predict the grant bandwidth from the OLT, and in this paper, the value of each queue report field is decided according to the prediction result. The simulation result shows that the ASPQR grants more bandwidth to ONUs as compared to other MQR schemes. Therefore, the average packet delay and packet loss ratios are improved. The improvement is as high as 50% in terms of the packet loss ratio.

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