由於長距離乙太被動式光纖網路具有能夠降低佈建成本和簡化都會網路與區域網路架構的特性，使得長距離乙太被動式光纖網路已成為一個具有發展性的寬頻接取技術。長距離乙太被動式光纖網路是將原本支援的距離由20公里增加至100公里，因此長距離乙太被動式光纖網路之來回傳輸時間亦會隨著距離而增加。而這增加的來回傳輸時間主要會影響到封包的傳輸延遲時間以及造成頻寬的使用率不佳，使得封包的傳輸延遲時間大幅上昇以及整體的頻寬使用率下降。因此，為了解決這兩個主要問題，過去所提出的方法大都是集中式的頻寬分配演算法。集中式分配演算法是由光纖線路終端器收集全部光纖網路單元的頻寬要求資訊，再由光纖線路終端器集中計算分配頻寬，最後再將計算結果傳回至光纖網路單元執行。然而，上述的方法會受限於光纖終端器與光纖網路單元之間的實體距離影響，這是因為光纖線路終端器與光纖網路單元必須要互相傳送訊息，這一來一往造成的頻寬閒置時間，會使得網路頻寬使用率不佳。此外，因為長距離乙太被動式光纖網路通常都用於範圍較廣及高分流比的網路環境下，即長距離乙太被動式光纖網路會比一般的接取網路服務更多的使用者。因此，目前只使用單一波長傳輸之長距離乙太被動式光纖網路並不能提供足夠的頻寬給眾多的使用者。為了解決上述問題，本碩士論文在分波多工長距離乙太被動式光纖網路環境之下提出一個基於光纖網路單元的分散式頻寬分配演算法。本碩士論文所提出方法是利用光纖波導光柵模組使得光纖網路單元之間具有互相傳輸溝通的能力，因此光纖網路單元之間可利用光纖波導光柵模組互相傳送控制訊息。當所有的光纖網路單元都收到了來自於其他光纖網路單元的控制訊息之後，就可以各自執行頻寬分配演算法，依序將資料上傳至光纖線路終端器而不會產生碰撞。因此，光纖網路單元就不用透過光纖線路終端器的排程，可減少來回傳輸造成的閒置時間，如此一來，便能大幅降低封包傳輸延遲時間以及提昇整體網路頻寬的使用率。最後，本碩士論文將進行一系列電腦模擬實驗，並與其他已提出的頻寬分配演算法做比較，結果顯示本論文所提出機制的確實能較其他機制達到較佳的效能。

The extended network span of Long-Reach Ethernet Passive Optical Networks (LR-EPONs) has become a promising access technology due to reducing the expenditure cost and simplifying the Metropolitan Area Network (MAN) architecture. However, the increased propagation delay also leads to a significant packet delay time and results in a poor bandwidth utilization. Most of previous proposed Dynamic Bandwidth Allocation (DBA) schemes take a centralized approach., which suffers low performance because of the long Round Trip Time (RTT) between the Optical Line Terminal (OLT) and Optical Network Units (ONUs) in LR-EPONs. On the other hand, since the LR-EPON is designed to have long reach and support more users, it needs more bandwidth to accommodate the increasing bandwidth demand. Thus, this study proposes an ONU-based Decentralized DBA (OD-DBA) in a Wavelength Division Multiplexing (WDM) LR-EPON. To facilitate the decentralized DBA scheme, an Arrayed Waveguide Grating (AWG) module is used in the place of splitter to enable information exchanging between all ONUs. By doing this, the proposed scheme is able to avoid the long RTT issue and achieve high bandwidth utilization. Finally, a series of computer simulations are systematically performed. The results obtained from the simulations show that the proposed scheme achieves a significantly higher efficiency than those of other DBA schemes.

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