在ATM網路上改善服務品質之優先序緩衝區管理方法

Abstract

寬頻整合服務數位網路(B-ISDN)被期望有效地支援多媒體資訊的傳輸，而 ATM網路正是一個適合此種網路的主要技術。因此，當我們在設計一個ATM 交換機輸出緩衝區時，我們必須考慮到能夠支援多類別多種不同服務品質 的需求。我們提出一個新的緩衝區管理方法，在有限的緩衝區資源下，使 網路達到較好的服務品質，並且期望在公平的原則下對品質優先序較高之 封胞 (Cell)做較佳的服務。此方法包括一個以封胞流失率監督器(CLR Monitor )控制且動態調整最大佇列長度及基礎保護門檻的智慧型緩衝區 管理部分，和一個利用到期(due time)概念藉以提供各類別相對較好延遲 品質，稱為(EEDF)的服務原則。在我們的模擬中，假設EEDF的服務速率 為155.52 Mbps，且原始流量模式採用所謂的「Burst-Silence traffic model」。最後，我們將以所提出的這種緩衝區管理法和單一共享先進先 出及固定式分離佇列長度這兩種緩衝區管理方法，針對服務品質做一個比 較。經過比較結果，若考慮到所有類別服務品質的達成度及各類別之間的 公平性問題，我們建議的方法將是最佳的一種。 Broadband Integrated Services Digital Network (B-ISDN) is expected to efficiently support multi-media information transfer in which each medium has its own grade of service (GOS) require- ments. The asynchronous transfer mode (ATM) is the key technology. When designing the output buffer in an ATM switch, the supporting to different kind of QOS for multiple classes should be considered. We propose a new buffering scheme to maintain the different kind of QOS for multiple classes with finite resource (buffer) and to provide the higher priority class with the better service under fair condition. The proposed scheme consists of an intelligent buffer management method to adjust a maximum queue size and a protective threshold for each class dynamically by monitoring the cell loss rate of each class, and a service discipline called Earliest Expected Due- time First (EEDF) to gain a better cell delay quality for each class individually by using a due time concept [5]. Assuming that ATM transmission rate of 155.52 Mb/s is considered as EEDF service rate of simulation. And we use the burst-silence traffic model for simulating the source. Comparisons are made for QOS among a single FIFO buffering scheme, a fixed-length separate queue buffering scheme, and our proposed priority buffer management scheme. Our proposed scheme is the best one if we consider the fairness and achievability of QOS of all classes.