心理物理學導向的網路電話頻寬分配機制設計

Abstract

如何設計一個好的傳輸速率調變機制使網路服務的效能提升是研究者長久以來不斷探究的問題。其中調變機制直接關係到網路資源運用上的兩難：公平性與服務效能。當部分網路服務占用大量的傳輸頻寬以提升自身服務品質時，用戶群體的服務效能及資源分配的公平性將被犧牲。有鑒於此，源於無線網路排程研究的｢比例公平原則｣在兩難困境之中提供了可行的解決方案。不同於以往的研究單純將此原則用於服務品質的量化計算，我們利用它在定義上與體驗品質的關係來建立資源分配中的效能函數。此研究以網路電話服務作為實驗對象，並以使用者研究實驗找到存在於傳輸速率和體驗品質之間普及性的對數關係。此對數關係保證了比例公平原則下的資源分配平衡點能為用戶群體同時帶來公平性及整體效能的提升。因此，我們設計出簡練的速率調變機制將傳輸速率以指數關係分割成若干級別。透過數學證明與程式模擬，我們的機制確實能使用戶間的頻寬分配達到比例公平並使用戶數與體驗品質獲得顯著提升。

Rate adaptation is one of the classic problems in data networking. The challenge here is to balance two seemingly contradictive objectives: performance and fairness. Increasing the sending rate typically enhances the delivery quality. However, extra bandwidth for some implies fewer resources for others. The concept of proportional fairness has risen as a plausible compromise. Although this approach has become almost a cliche for rate allocation based on QoS-based utilities, there is still a lack of systematic research involving real-time multimedia streams in which the quality of user experience (QoE) serves as a better utility function. Focusing on VoIP calls, this study conduct a user study and identifies a ubiquitous logarithmic relationship between the sending rate and user experience. The logarithmic relationship warrants that a proportional fair solution is also a fair solution (i.e., a proportional fair solution optimizes overall performance and the number of calls served). Inspired by this logarithmic relationship, this study presents a simple scheme that exponentially quantizes the steps of rate change. The analysis and simulations in this study show that the resulting bandwidth allocation converges to proportional fairness.