探討使用TCP友善規劃器來減少連續多媒體資料流對TCP資料流的影響

Abstract

近年來串流流量在網際網路的世界中快速的成長，由於一些連續性媒體上的考量，這些串流流量大部份比較傾向於採用UDP做為其傳輸層的通訊協定。此外，RTP以及RTCP亦經常被多媒體傳輸的應用程式所採用，用以加強UDP傳送多媒體資料的能力。然而，這些協定並沒有提及任何擁塞控制的機制，因此當TCP及UDP的流量共存時可能會導致擁塞崩潰的現象發生，因而降低網路的品質及使用率。 在本研究中，我們提出一個稱為適應性規劃器的機制，其由rate-smoothing元件及TCP-Friendly擁塞控制元件所組成。此機制可用以調整串流流量的傳送速度以減少對TCP資料流的傷害。首先適應性規劃器會攔截RTP及RTCP的封包並取得所需的流量資訊，當頻寬資源足夠時，rate-smoothing元件利用排隊長度的變化動態的估計串流流量的到達速度並減少傳輸速度的震盪。此外，當網路發生擁塞時，TCP-Friendly擁塞控制元件會迫使串流流量能夠反應擁塞並防止TCP資料流發生飢餓現象。最後，由模擬的結果顯示適應性規劃器使網路的有效性由92.5%提升至99.5%，並且能減少串流資料流對TCP資料流的影響。 關鍵字: 規劃器，TCP友善擁塞控制

In recent years, streaming traffic has been employed in the Internet world with a rapid increase, most of which is preferably carried by the UDP transport protocol because of certain continuous media concerns. In addition, the RTP and RTCP, embedded with appropriate information, are generally employed to enhance original UDP with continuous media applications when multimedia data are transmitted. However, these protocols do not address any mechanism for congestion control and thus under such a non-congestion controlled situation, coexisting TCP and UDP traffic can lead to congestion collapse, which degrades the performance and utilization of the network. In this work, we propose a mechanism called Adaptive Shaper (AS) inclusive of the rate-smoothing component and the TCP-Friendly congestion control component. It is expected to reduce the harm for TCP flows by gathering the network traffic loading information and adjusting the sending rate of the streaming flow. As the bandwidth resource is sufficient, the rate-smoothing component takes advantage of the variations in queue length to dynamically estimate the arrival rate of the streaming traffic which reduces the fluctuation of the rate effectively. While, as the network is congested, the TCP-Friendly congestion control component forces the streaming flow to respond to the congestion and immediately prevent TCP flows from starvation. Finally, the simulation results present that the adaptive shaper increases the efficiency of the network form 92.5% to 99.5% and reduces the impacts of continuous media on TCP flows.