跨環的彈性分封環網路之智慧型全域公平控制器

Abstract

IEEE在標準802.17中提出了一個適用於下一代都會區域網路(Metropolitan Area Network)的彈性分封環(Resilient Packet Ring)架構。基於頻寬的需求，以及為了服務更廣大的區域，多個彈性分封環可以橋接在一起，形成一個跨環的彈性分封環網路。先前的研究著重在於整個跨環的彈性分封環網路的拓墣發現，以減少泛流式(flooding)廣播的方式來傳送跨環的資料。另外也有專注於確保跨環的資料能夠達到全域公平性的研究，但是他們並不能完全保證不會有緩衝區溢位的情形發生。目前已經有許多關於單一個彈性分封環之本地的公平演算法被提出，但是本地的公平演算法並不適用在跨環的資料所需要達到的全域公平性。因此，我們根據一個稱之為Ring Ingress Aggregated with Spatial Reuse (RIAS)的本地性公平定義，發展出一套全域性的公平準則，並且提出一個智慧型全域公平控制器。這個智慧型全域公平控制器能提供全域公平、維持本地性公平，而且完全對緩衝區溢位的問題免疫。另外我們也提出一個權重路徑選擇器，藉著有效率的判斷，來選擇沒有被使用的路徑來傳送資料，以提升系統的頻寬使用率。在模擬結果中可以發現，針對不同的拓墣網路環境以及不同的資料需求模式，智慧型全域公平控制器都有著良好的表現。

Resilient Packet Ring (RPR) is designed for the next generation Metropolitan Area Network (MAN), also known as the IEEE 802.17 standard. Multiple RPRs can be connected together to from a bridged RPR network (BRPR) to support the wide area and the growing demands of bandwidth. Previous researches have focused on topology discovery without flooding inter-ring traffic, whose source and destination nodes are on different rings; also, assurance of global fairness for inter-ring traffic but not always immune to buffer overflow. Many local fairness algorithms have been proposed, but they are unable to ensure fairness for inter-ring traffic. So, we develop the global fairness criteria inherited from RIAS local fairness reference model. Then we propose an intelligent global fairness controller (IGFC) to provide global fairness for inter-ring traffic, maintain local fairness for intra-ring traffic, and guarantee the immunity against buffer overflow. A simple weighted ringlet selector (WRS) is also proposed to promote bandwidth utilization by employing the unused ringlet. We justify that IGFC achieve better performance under various topology and traffic patterns.