由於地面網路分布不均，導致網路傳輸資源在市區與郊區環境下分配不均，不容易滿足不同的網路服務的QoS需求，因此採用衛星網路輔助地面的路由以促進良好QoS需求。本論文研究方法的概念是將資料透過低軌衛星進行傳送以輔助地面網路，將對網路流量進行建模，並同時納入延遲、封包遺失率以及頻寬的均衡考慮，以提高數據傳輸的效率。
低軌衛星在軌道上高速移動，衛星之間的鏈路(ISL)頻繁切換網路拓樸不斷變化，導致傳送時容易發生封包遺失，一般封包遺失使用重傳路由機制會導致不斷的拆分及重組封包和延遲增加，需要動態調整路由或增強鏈路的連接以確保資料的正確傳輸。因此本文的研究提出一套基於SDN的QoS衛星路由方法，這個方法的設計主要是根據使用者對於不同網路服務的需求，其中包含資料流的延遲、頻寬、封包遺失率透過SDN進行集中控制，相較於一般集中式路由，我們考量到衛星網路的移動性，將資料流和衛星設計為隨時間改變的動態拓撲，此外將資料流根據延遲進行分流以實現端到端資料傳輸路徑，最小化傳輸延遲和封包遺失率。
本文的研究建立一套Mininet 的無線環境結合Ryu 模擬平台建構基於SDN 的衛星拓樸，以Python 撰寫控制器的路由決策以進行延遲、封包遺失率以及吞吐量的評估，根據實驗結果，我們的方法與相較於DSP 和 DRA 以及calen路由方法，我們的方法能夠在需求數量龐大的情況下有效減少傳輸延遲和封包遺失率。

Due to the uneven distribution of networks scattered on the ground, network transmission resources are unevenly allocated in urban and suburban environments, making it difficult to meet the QoS requirements of different network services. Satellite assisted networking technologies are thus employed to enhance ground routing and promote satisfactory QoS requirements. The conceptual approach of this thesis involves utilizing low Earth orbit (LEO) satellites to assist data transmissions along with ground networks. The study in this thesis models network traffic paradigms and takes account of latency, packet loss rate, and bandwidth balance, all aimed at improving data transmission efficiency.
LEO satellites move rapidly along their orbits, and the inter-satellite link (ISL) frequently switches, causing packet loss during transmissions. Traditional packet loss recovery mechanisms lead to constant fragmentation, packet reassembly, and increased latency. To remedy these issues, it is necessary to perform dynamic routing adjustments or enhanced link connections to ensure accurate data transmissions. Hence, this study proposes an SDN-based QoS satellite routing method. The design of this method primarily revolves user demands for different network services, including multi-fold aspects like data flow latency, bandwidth, and packet loss rate, all centrally controlled through SDN. In contrast to conventional centralized routing, we account for satellite network mobility by designing data flows and satellites as dynamically changing topologies over time. Additionally, data streams are dynamically routed based on latency to achieve end-to-end data transmission paths, minimizing transmission delay and packet loss rate.
This study establishes a Mininet wireless environment combined with the Ryu simulation platform to construct an SDN-based satellite topology. Routing decisions are scripted in Python for measure evaluation of latency, packet loss rate, and throughput. Based on experimental results, our approach outperforms DSP, DRA, and calen routing methods, because of effectively reducing transmission delay and packet loss rate, especially under high demand scenarios.

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