受到封包網路原本忽略時效性特性之影響，對時效性要求極高的多媒體網路服務，如Voice over IP (VoIP)以及Video on Demand (VoD)在All-IP整合的核心網路上提供時，其服務品質低於傳統之電路交換網路。
封包在網路的傳遞過程中受到各種因素之影響，於到達目的地時，可能會造成long delay time，high jitter或packet loss，而在目的地端幾乎已經沒有補救機會，故而如果能在傳遞的過程中，依封包的時效性及重要性做適度的次序調動(rescheduling)而不要依序傳遞(FIFO)，讓過遲的封包提前送出，而將有時間餘裕的封包稍緩送出，如此截長補短，可提高網路效能及整體QoS滿意度。
我們在BBQ (Budget-Base QoS)的架構下發展一套簡單而有效的方法，在單佇列(Single Preemptive Queue)及多佇列(Multiple FIFO Queue)的router架構下，根據封包時效性及重要性賦予合適的profit function，並參考封包在後續路程上各router的負載狀態以便能更精確預估封包是否能及時到達目的地並調整profit function參數以調整封包的送出順序，如此能提高排程的效能。
我們先對單一服務等級的封包排程進行研究，獲得參數調整之技巧，再根據其結果設計多服務等級的封包排程方法，其重點在於如何調配profit function給不同的服務等級。
我們藉由NS-2模擬模擬器進行實驗，評估本方法的效能，實驗結果顯示我們的方法可以較每個router僅根據自身所知的資訊進行排程更可以有效提高網路效能，且能對不同的服務等級做差異化處理以提高整體QoS滿意度。最後在多等級服務的實驗環境及評估指標下，網路高負載的情況，本方法與Simulated Priority Queue排程演算法比較可以提升34%的整體滿意度。 / Running time sensitive multimedia services such as Voice-over-IP (VoIP) and Video-on-Demand (VoD) on All-IP networks may have lower quality than that on the traditional circuit-switched networks.
Influenced by many factors, packets transported on a packet-switched network, may suffer from long delay time, large jitter and high packet loss rate. When a packet arrives its destination late, there is no way to correct the problem. Thus, it will be beneficial if routers could forward packets base on their timeliness and importance, instead of using First-In-First-Out (FIFO) service plan, giving important late packets proper precedence. The overall QoS satisfaction will be improved significantly.
In this thesis, we develop a simple and effective scheduling policy based on this concept for the environments where packets have predefined hop-by-hop time schedule. Routers are assumed in two different queue architectures: ideal Single Preemptive Queue router and practical Multiple FIFO Queue router. To forward a packet, a router first assigns a suitable profit function to the packet based on its timeliness and importance as well as the loading status in its succeeding routers along its predefined traveling path, then inserts the packet into an appropriate position in the output queues. Taking the loading status of succeeding routers into account could predict more accurately whether the packet could reach its destination on time or not.
We conduct the research for the single service class environments first to learn the characteristics of this new scheduling policy, and then for the multiple service class environments based on the knowledge acquired. The challenge is to find the best way to assign proper profit functions to different classes of packets in order to utilize resources more wisely, e.g. urgent and important packets get precedence.
We evaluate the performance of this approach by simulation using NS-2 network simulator. Simulation results show that our approach outperforms our previous version which doesn't take the loading status of succeeding routers into account. Furthermore, our approach can outperform the Simulated Priority Queue by at least 34% under heavy load and our evaluation metrics.
| Identifer | oai:union.ndltd.org:CHENGCHI/G0094753041 |
| Creators | 溫永全, Wen,Yung-Chuan |
| Publisher | 國立政治大學 |
| Source Sets | National Chengchi University Libraries |
| Language | 中文 |
| Detected Language | English |
| Type | text |
| Rights | Copyright © nccu library on behalf of the copyright holders |
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