近年來在被動式光網路(Passive Optical Networks, PON)的進展上，佈建線路上有著延伸原本短距離(Short Reach)的線路至長距離(Long Reach)，稱做長距離被動式光網路(Long-Reach Passive Optical Networks, LR-PON)，此架構用以服務更多距離較遠的使用者，如此一來位於在中央機房(Central Office, CO)的營運成本就可以降低。另一方面，由於位在CO的光網路終端(Optical Line Terminal, OLT)與光網路單元(Optical Network Unit, ONU)間距離的增加，傳統動態頻寬分配演算法(Dynamic Bandwidth Algorithm，DBA)在OLT與ONU間訊息傳播延遲(propagation delay)的增加下，導致其效能降低，因此在LR-PON下的DBA必須重新設計及審視。
在本論文中，我們提出了multi-thread fitting scheduling timing-elastic weighted granting (MT-FST-EWG) 動態頻寬分配演算法，MT-FST-EWG是合併了兩個方法FST-EWG及multi-thread polling (MTP)的優點並改善了FST-EWG在LR-PON下因為long propagation delay problem產生的效能不足。MT-FST-EWG在方法分析及模擬結果的輔助驗證下，成功的解決在LR-PON下產生的long propagation delay problem，相較於原始的MTP，MT-FST-EWG的封包延遲也表現較好。

In recent years, passive optical networks (PONs) have been widely chosen for deploying optical access networks. With the widespread deployment of PONs, research focus has shifted to their scalability, with longer reach and higher split ratio. By exploiting both optical amplifiers, long-reach PONs (LR-PONs) extend the coverage of a PON from short-reach 20 km to 100 km and beyond. By reducing the number of network elements, the network’s Capital Expenditure (Capex) and Operational Expenditure (Opex) can be reduced.
On the other hand, due to the increased distance between optical network terminal (OLT) and optical network unit (ONU), the propagation delay increases to 1ms. When an ONU requests upstream bandwidth, it will take a longer time to receive the acknowledgement from the OLT before it can transmit its upstream packets. Thus, the traditional dynamic bandwidth allocation (DBA) in LR-PONs must be redesigned and under review.
In this thesis, we propose a multi-thread fitting scheduling timing-elastic weighted granting (MT-FST-EWG) dynamic bandwidth allocation algorithm (MT-FST-EWG) which is to merge the advantages of both fitting scheduling timing-elastic weighted granting (FST-EWG) and multi-thread polling (MTP) and improve the effectiveness of FST-EWG shortage in LR-PON. We evaluate the throughput-delay performance of MT-FST-EWG, FST-EWG and MTP. We find that MT-FST-EWG gives lower delays and idle times than FST-EWG and MTP. At the same time, the propagation delay problem FST-EWG faced was solved by MT-FST-EWG.

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