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Congestion control is an important function in a multimedia application. Since multimedia packets are mostly transmitted in UDP, which lacks the congestion control mechanism in TCP, a separate congestion control is necessary to avoid excessive packet losses and to be fair with competing TCP flows. As UDP congestion control is rate-based, unlike the window-based one used in TCP, end-to-end available bandwidth estimation can play a critical role in UDP congestion control. This paper proposes a new method to estimate the available bandwidth based on the delay trend detection, which is suitable for a multimedia application. We deduct the relationship between delay trend and available also show the Internet experiment results. Various practical time measurement errors are analyzed and their countermeasures are proposed.