The Study on State Transition Behavior of The Shared Buffer Switch and Call Admission Control Criterion in the ATM Network
在非同步傳輸模式綱路中，傳輸速度遠高於傳統使用的綱路。然而其亦面臨一些問題。例如，假若綱路正處於極度擁塞狀態，亦即，過多從訊號源送出的細胞由於擁塞而被丟棄時，此時往往難以回復至正常的狀態。因此，找出一個能使綱路正常受控的方法顯得十分重要。關於擁塞預防的其中一個重要主題為呼叫建立控制（Call Admission Control），其控制準則為須基於一些可信參數，如：服務品質參數（QoS）等。
For years, efforts have been made to improve the communication quality and bandwidth for the increasong traffic volumn of the communication needs. However, today the transmission and switching for multimedia data have met big problem since it contains a large variety of traffic sources, with many sources different characteristics. With the introduction of B - ISDN, the problem seems to be solved well. Among the techniques used to implement the B - ISDN architecture, the ATM (Asynchronous Transfer Mode) is found to be the most promising protocol due to its high efficiency and flexibility. In an ATM network, the transmission speed is much higher than that in the traditional networks. But some problems are also met in the network. For example, if the traffic state of the network is at serios condition that is, too many cells generated from the transmitted sources are discarded due to netowork congestion, then in most cases it is hard to recover the netoork to normal state. Therefore, a good way for the network system to keep the network under control is very important. One of the important topic for congestion avoidance is the CAC (Call Admission Control). The admission decision should be made based on some convincing factors, such as Qos. Here we will propose a method for estimating instantaneous cell loss rate and thus use the result to determine whether or not to accept a new call. The original cell loss rate is measured based on the current traffics tate of the ATM network. And the increment in the instantaneous cell loss rate when a new call asks for connection is then calculated based on some mathematical analysis. We use some mathematical models to describe the ATM network, so that analysis on instantaneous cell loss rate could be proceeded well. What is amazing is that the result of the estimated formula is quite simple. This would do help to the call admission control since the calculation work for the system to make the decision could be much lessen.
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