在差別式服務網路內針對即時及事前要求的頻寬代理器之允入演算法

Abstract

差別式服務內的品質服務可分成兩種類型─事前要求(Book-Ahead requests, BA requests)與即時要求(Instantaneous Requests, IRs)。當一個已經允入的事前要求正開始傳送資料時，可能因頻寬不足而使得部份正在進行中的即時要求被中斷。因此，為了避免正在進行中的即時要求被中斷，以致浪費更多的頻寬。允入控制(Admission control)在對即時要求做允入決策時必需先預測其連線時間，也就是所謂的look-ahead time，而後檢視在這一段look-ahead time內的剩餘頻寬是否足以滿足新進的即時要求。如果頻寬不足，則此一即時要求將不會被允入。在我們這篇論文裡，描述了一個名為Application-aware look-ahead的允入演算法。這個允入演算法將依其應用軟體的差異而給予不同的look-ahead time。此外，當允入控制對事前要求作即時性回應的允入決策時，它並無法得知後來的事前要求是否會帶來更多的報酬。所以，我們亦提出了可延後回應的事前要求允入方式。經由模擬的結果證實了Application-aware look-ahead成功地降低了即時要求被中斷的機率及因中斷而浪費的頻寬。而可延後回應事前要求的允入方式也能得到了更好的報酬。

The Quality of Service (QoS) reservations in Differentiated Service (DiffServ) networks could be classified into two sets, Book-ahead (BA) requests and Instantaneous Requests (IRs). When an admitted BA request starts to be served, some ongoing IRs may be dropped because the available bandwidth is insufficient for the BA request. In order to prevent the admitted IRs being dropped, thus causes wasted revenue, the admission control should predict the lifetime, i.e. look-ahead time, of the IRs. Then it checks if the available bandwidth during the look-ahead time is sufficient for the incoming IRs. If not, the IR should be rejected. In this paper, we propose an Application-aware look-ahead admission control for IRs. It determines the different look-ahead time for different application types that the IRs belong to. Furthermore, when the admission control does immediately decisions to admit a BA request, it does not know whether the subsequent coming BA requests would bring more revenue. Therefore, we also propose the Deferrable model of the admission control for BA requests. The simulation results have shown that the Application-aware look-ahead admission control successfully reduces the dropping probability and wasted revenue of IRs. The Deferrable model indeed makes more BA revenue.