使用連線負載平衡上之即時TCP路徑選擇演算法

Abstract

連線負載平衡之最終目標，是將各連線分配到一個最好的對外連線上。傳統的分配方法只以接取網路的狀態來作判斷的依據。這樣的做法即使可以達到很高的頻寛使用率，但TCP連線卻是效能不佳的情況。我們提出了一個新的方法，利用即時量測round trip time的機制，對每個連線求得最大的傳輸量。 RTT的值是透過TCP三方向建立機制在同一時間去取得。加上以統計的方式取得的packet loss的預估值，以及附以各個連線的狀況，在這演算法中，便能以TCP連線速度，用以選擇一個最佳的對外連線。 實驗的結果顯示此演算法的正確率超過70%。此外對擁有多個的對外連線的頻寛來看，能有效使用至實際可以達到最高傳輸量的90%。

Dispatching connections through good links is the ultimate goal in access link load balancing. The traditional dispatching method is only based on the condition of the access links to ISP. It may achieve high utilization on the access link but poor performance on connection throughput. In this work, we propose a new approach to maximize the per-connection end-to-end throughput by on-the-fly round trip time (RTT) probing mechanism. The RTTs through all possible links are probed during the three way handshaking stage of the TCP connections. Combined with the statistical packet loss ratio and the passive collected link metrics, our algorithm can real-time select a link from multiple access links, providing the maximum throughput for a TCP connection. The experiment results show that the accuracy to choose the best outgoing access link is over 70\%. Moreover, it fully utilizes the multiple access links environment, achieving over 90\% of the maximum possible throughput.