為了提供許多新的多媒體網路應用的需求，立即式保留(immediate reservations)及預先式保留(advance reservations)機置相繼被提出。當使用者事先知道其連線起始時間、連線結束時間、以及使用頻寬等資訊，即可透過預先保留機置做預留的動作，以避免在要求建立連線時因資源不足而被允入控制(admission control)所拒絕。預留頻寬的作法可使系統管理者更有效的安排其資源，讓系統的頻寬使用效能提昇。然而在此種機置下，由於立即性保留連線的優先權比預先保留連線低，因此當已保留頻寬的預留連線真正啟動卻遭遇頻寬不足時，一些立即性保留連線會被中斷，失去其原有的服務保證(Quality of Service, QoS)，改採盡力式服務。
　　以往研究計算立即性保留連線之中斷機率，皆假設預先保留連線皆會在預定的時間準時建立連線，但一般使用者的行為習性並不是如此；使用者可能提早或延遲建立其預定的連線，因此本論文在允許提前或延後建立連線時間的環境下，提出一個更準確地評估其立即保留連線的中斷機率，實驗結果也證實我們所提出的方法可更精準的計算出連線中斷機率，如此可減低實際中斷的情況發生，確保其所要求的服務品質。

　　To satiety the QoS requirements of many new multimedia applications, the mechanisms of immediate reservations and advance reservations were proposed. Users make reservations in advance when they can provide the connection information, including its starting time, duration, and required bandwidth, in order to avoid being rejected by the admission control because of the insufficient available resource at connection establishment. The advance reservation can provide the network message to control network resources efficiency, increasing the resource utilization. Because, immediate reservation calls (IR calls) have a lower priority than advance reservation calls (BA calls), and some of them would be interrupted if no enough bandwidth to be available at the establishment of a BA call. The IR call will be interrupted, and thus lose its QoS guarantee.
　　In many previous studies, the interrupt probability of IR calls is under the assumption that BA calls start their connections at the instant they reserved. However, user’s common behavior makes this assumption be not true. Users may establish ahead or behind their connections. Thus, we present a more accurate way to estimate the interrupt probability of IR calls in the environment where BA calls with inexact connection arriving times. The results show that our calculation really gets a higher and more correct interrupt probability of a IR call so that its actual blocking probability is higher and its actual interrupt probability is lower.

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