下一代之行動/無線通訊網路預期將會提供各種服務，例如語音，視訊，多媒體數據等。如果要能在無線鏈結上成功支援多媒體流量，無線網路之終端系統之間之服務品質必須獲得保證。我們提出一種運用限制與降級之連結允入控制(CAC-RD)以用於無線網路，其中運用適應型頻寬配置來提供多種位準之服務品質給使用者。我們推導相關之數學解析模型，以及新連結阻塞機率，交遞失敗機率，與平均頻寬之數學表示式。由於相關數學過於複雜，降級比率與升降級頻率是藉由電腦模擬來求得。電腦模擬程式是以C語言自行撰寫，以驗證解析結果之準確度，以及瞭解及控制各種連結允入控制方法之細節。我們顯示，解析結果合理地接近模擬結果，尤其是當提供負載較輕時。為比較起見，運用限制，但不運用降級之連結允入控制(CAC-R)之模型也受到展示。我們發現，使用服務降級(CAC-RD)之新連結阻塞機率與交遞失敗機率皆低於未使用服務降級(CAC-R)之新連結阻塞機率與交遞失敗機率。限制臨限值，流量混合比率，與連結服務時間對於效能量度之影響也受到探討。我們獲得下列結論：無線網路之連結允入控制應同時考慮提供負載，流量混合比率與連結服務時間，以同時滿足所有必要之服務品質要求。

It is expected that various kinds of services, e.g., voice, video, multimedia data,etc., will be provided in the next generation of mobile/wireless communication systems. For multimedia traffic to be supported successfully over wireless links, it is necessary to provide quality of service (QoS) guarantees between the end-systems in wireless networks. We propose a call admission control with restriction and degradation (CAC-RD) for wireless networks which uses adaptive bandwidth allocation to provide users multi-level QoS. We derive the associated analytical model and the expressions for new call blocking probability, handoff failure probability, and average bandwidth. Due to mathematical complexity, degradation ratio and upgrade/degrade frequency are found via computer simulation. The simulation program is written in C language not only to verify the accuracy the analytical results but also to understand and control the details of various CAC schemes. It is shown that the analytical results are in reasonable agreement with simulation results, especially when the offered load is light. For comparison purposes, the model for CAC with restriction but no degradation (CAC-R) is also shown. It is shown that, with service degradation (CAC-RD), the new call blocking probability and handoff failure probability are smaller than those without service degradation (CAC-R). The effects of restriction threshold, traffic mix and call holding time on performance measures are also studied. It is concluded that CAC for wireless networks should take into account the offered load, traffic mix, and the call holding time in order to satisfy all required QoS requirements.

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