同步傳輸模式中突增性資料量造成網路壅塞之控制管理研究

Abstract

以非同步傳輸模式 （Asynchronous Transfer Mode, ATM）為交換技 術的網 路之中，對於在合理的成本之下滿足使用者所需的服務品質，是 非常重要的課題 之一。為了要有效地且公平地讓使用者分享有限的網路 頻寬資源，在非同步傳輸 模式網路中勢必要加入壅塞控制機制。 為了要提供使用者公平且高效率的網路傳輸品質，使用者的資料傳輸必須 要 依據其進入網路時與網路所建立的使用限制來動作，而這些使用限制 就是在敘述 網路使用者的資料傳輸特性。同時，網路自身也必須要具有 監控的機制以來保證 整體的網路傳輸品質不至於被任何使用者違反使用 限制的舉動影響。隙漏水桶法 （Leaky Bucket）就是其中一個廣為所知 的監控機制。但是此法並沒有參考封包 傳輸特性，而可能將重要的封包 丟棄或標示這樣的忽略，將會降低網路的傳輸效 率。 在本研究中，針對上述問題提出一個稱做具有雙重優先權控制之隙漏水桶 法 的新的機制。這個新的機制在傳統的隙漏水桶法加入了優先權控制及 回饋機制。 當網路壅塞時，我們提出的機制會依循各個封包特性而將超 出網路資源的封包依 優先權丟棄，而回饋機制將通知資料傳輸者目前傳 輸狀況，動態調整其傳輸速率 以減輕網路壅塞時可能造成的損害。這個 機制試圖在網路傳輸品質及有限的網路 頻寬中找到最佳的平衡點。根據 模擬結果，這個新的機制是能有效的在網路壅塞 情況時做出適當的控制 管理。 An ATM-based network must provide satisfactory quality-of- services for all network users with acceptable implementation costs. To allocate shared network transmission bandwidth and buffer capacity effectively and fairly, an ATM-based network should be equipped with a congestion control mechanism. After a connection is setup, traffic from users may need to be monitored and enforced to comply with the declared traffic parameters to provide good performance and guarantee fairness among users. The traffic parameters which could be established at the time of its admission to the ATM network are used to describe accurately the type of traffic and its characteristics. A policing mechanism which is based on the traffic parameters is needed to ensure that any violation in the user's traffic characteristic will not affect the overall performance of the network. The leaky bucket mechanism is a well-know approach. However, it is carried out at the network edge, which opens the possibility of cells being discarded or marked without reference to the actual message of traffic characteristics. This may lead to degradation of the networkperformance. In this thesis, we propose a new policing mechanism, called the leaky bucket with double-two priority control (D-T scheme), to solve this problem. The D-T scheme combines the traditional leaky bucket mechanism with a priority control function and a feedback mechanism. Under the condition of congestion, the D-T scheme will discard the excess cells with reference to their traffic characteristics and inform the transmitter with the traffic status to change its transmission rate to diminish the damage of congestion. The D-T scheme is a bandwidth control mechanism which maintain the balance between quality-of-services and network resource utilization. Simulation results show that the D-T scheme is an effective approach of reactive congestive control.