因應網際網路應用的趨勢，提升連接每個家庭的接取網路效能是必行的，本研究選擇最有潛力被普及的EPON (Ethernet passive optical network)進行效能提升，由於EPON中的上傳頻寬是被所有ONU (optical network unit)所共享的，必須要有一個好的頻寬分配演算法避免ONU間的上傳資料發生碰撞。一個好的頻寬分配演算法需要高的頻寬率並且支援QoS (Quality of Service)，但OLT (Optical Line Terminal)收到所有ONU的REPORT後再執行頻寬分配產生了一段idle time，為了達到高的頻寬利用率勢必要消除idle time進而達到高的頻寬利用率。另一方面，QoS也是EPON上一個重要的議題，由於EF (Expedited Forwarding)類別對delay與jitter delay要求較為嚴格，許多文獻提出先排程所有ONU的EF類別，排程完EF類別後再排程AF(Assured Forwarding)與BE (Best Effort)類別，藉此來提高EF類別的效能， 但在此先排程EF類別再排程AF與BE類別的架構中，有些文獻甚至沒有提出消除idle time的演算法，而有些文獻中消除idle time的演算法使用最後一個ONU的AF/BE來消除，有些文獻採用所有ONU的EF類別來消除idle time，但皆無法有效的消除idle time，導致頻寬利用率不佳。本研究提出一個演算法，利用所有ONU的AF/BE來消除idle time，當AF/BE可完整消除時，選擇適當ONU的AF/BE來消除，當所有ONU的AF/BE無法完全消除idle time時，彈性的加入下個週期的EF類別一起參與消除idle time，當所有下個週期的EF類別皆加入消除idle time仍無法消除時，再將剩餘未使用到的idle time頻寬分配給ONU使用。藉由彈性地使用某些ONU的某些class來有效的消除idle time，並藉由消除idle time有效的縮短週期時間，更增進EF類別效能。模擬結果也顯示本研究所提出的方法比現有的方法有較高的頻寬利用率，擁有較高的頻寬利用率進而改善dropping probability，並更加提升EF類別效能，包含EF類別的packet delay與jitter delay。

The Ethernet Passive Optical Network (EPON) has been considered an attractive solution to access networks due to its having properties of scalability and low cost. A critical issue in the EPON is the sharing of upstream bandwidth among optical network units (ONUs) , it must make good use of idle time to get high utilization. As technology matures, QoS (Quality of Service) issue becomes a key concern. Due to EF (Expedited Forwarding) traffic is both delay and jitter delay sensitive, and many studies have proposed a method to improve EF performance by dividing transmission into two parts. OLT (Optical Line Terminal) assign the EF transmissions of all ONUs first and the AF(Assured Forwarding)/BE(Best Effort) packets second, but there is no good solution designed to solve idle time problems completely using this mechanism. Some methods use the EF packets of all of the ONUs to eliminate idle time, and some methods used AF and BE packets from the last ONU to eliminate idle time. However, none of them can eliminate idle time completely. We proposed a mechanism to eliminate idle time efficiently by employing the AF/BE packets for all ONU in order to eliminate idle time. When the bandwidth of all AF/BE packets is not enough to eliminate idle time, the OLT pre-allocates EF packets for the next cycle by employing EF packets in addition to AF/BE packets so as to eliminate idle time. When employing AF/BE and EF packets for this purpose, there still is unused idle time bandwidth, and the OLT reallocates unused idle time bandwidth to an ONU so that it can transmit packets that arrive during the waiting time. By eliminating idle time efficiently, the cycle time is effectively shortened, leading to better performance of EF traffic. Detailed simulation experiments are presented to validate the proposed algorithm.

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