一個在 ATM 網路上端點對端點即時多媒體傳輸的同步方法

Abstract

寬頻整合服務數位網路 (B-ISDN) 利用 ATM 做為傳輸骨幹，它支援不同 的傳輸率與包括各種資料型態之多媒體資訊傳輸。而在傳輸過程中，往往 因為網路節點的擁塞而造成不同型態之媒體無法同時到達或及時到達接收 端，而造成了顯示過程的同步問題。本論文以一個網路上較高階層的做法 來確保在 ATM 上做「端點對端點即時多媒體傳輸」的效果，其主要目的 在有效控制並降低傳輸過程中可變動的時間延遲 (如緩衝區的等候延遲) 以使在可容許的最大延遲時間內讓資料送達目的地並成功的播放。我們提 出了一個在 ATM 交換機裡提供多階層緩衝區，以將不同延遲需求的資料 分別指定到不同服務速率的緩衝區，來讓總平均等候的時間減低。基於考 慮封包損失(cell loss)的程度，我們動態的調整分送原則是：若指定的 緩衝區已滿時，動態的轉送到較高階層的未滿緩衝區以同時確保封包不致 大量損失，也能保持原先需求的服務速率。在我們模擬實驗所得到的結果 顯示在相同的傳輸負載程度下，我們的方法比一般的緩衝區設計方式得到 了不相上下的封包損失率，但是平均延遲時間卻降低了。這表示在「簡單 設計」的原則下，我們的方法得到了一較好的結果。 Broadband ISDNs (B-ISDN) use ATM as its backbone transmission network. It supports various transmission rates and several data types of multimedia data communication. However, during the transmission, the congestion on each switching node may cause the different types of multimedia data arrive the destination synchronously or in time and then arises the problem of playout synchronization. This paper presents a high- level view of the requirements to guarantee the real-time multimedia traffic performance in an ATM switching network. The main goal for the end-to-end synchronization of multimedia traffic is to control the quality-of-service (QOS) and reduce the variable delay, e.g. queuingdelay, to meet the restriction of the total end-to-end delay, so that the transmitted data can be delivered to the destination in time before the associated playout time. We propose a multiple-queue scheme to offer the different service throughput to meet the required delay time. From the standpoint of cell loss, when the associated queue is full, we dynamically select a faster non-full queue to serve. Thus, we handle the cell loss rate as well as reduce the variable delay time. After simulation of our proposed policy, the results indicate that under the same traffic load, it brings a little better cell loss rate but a significant cell delay QOS than the other buffer management schemes. By means of the principle of simplicity, we show that our method achieves a better average QOS for the real-time multimedia traffic.