應用於VoIP系統之以軟體實現的H.323閘道器與代理轉碼器之嶄新互動架構

Abstract

在這一篇碩士論文當中，我們針對運作於個人電腦平台上軟體實現的 H.323閘道器提出了一個嶄新架構。這個動機是基於兩個觀察。首先，我們觀察到一個軟體實現的H.323閘道器的計算量負載，主要是來自於不同媒體格式的轉換動作，例如轉換語音的編碼格式。我們也觀察到一個網際網路電話終端機(在我們的系統中，網際網路電話終端機是建構在個人電腦上)或是一個軟體實現的H.323閘道器所需使用的CPU計算資源，有時會被作業系統切換到其他的工作；因此，一個正在進行中的網際網路電話可能會有瞬時的不順暢或中斷。因此我們提出一個代理轉碼器(proxy-TC) 架構來平衡網際網路電話所需的計算量負載，同時平緩所給定計算資源的浮動。根據我們的模擬顯示，在我們所提的架構之下，系統的容量和新進電話的阻斷率 (blocking probability) 會有相當大的改善。除此之外，我們的模擬結果也顯示，加入代理轉碼器之間的移轉機制(TC-handoff mechanism)，僅僅微量的提高新進電話阻斷率，卻可使電話中斷率 (dropping probability) 大幅的降低。

In this paper, we present a novel architecture for software-based H.323 gateways that operate over PC platforms. It is motivated by two observations. First, we found that the computation load of a software-based H.323 gateway is mainly contributed by media transformation activities, such as the transcoding of voice streams. We also observed that the CPU computation power of an IP call terminal (which is a PC in our system setting) or a software-based H.323 gateway may be unevenly switched to another task by the operation system; hence, an active IP call may experience occasional interrupts. We therefore propose a proxy–transcoder (proxy-TC) architecture to balance the computation load of, as well as to smooth the fluctuation of dedicated computation powers to, the IP call activities. Our simulation showed that both the system capacity and the new call blocking probability can be significantly improved under our proposed architecture. Besides, by adding an additional TC-handoff mechanism, the active call dropping probability can be drastically decreased at the expense of a little increase in the new call blocking probability.