應用於終端設備以提供TCP相等性與閘道器上以排程請求回應的公平控制方法

Abstract

為了在網路上傳送封包，資料流可能需要為頻寬而競爭。當資料流為Internet上頻寬競爭時，公眾公平性是需要被維持的，相對的，當資料流於私有的接取路徑上競爭時，則私有公平性可能需要被維持。為維持公眾公平性，不同於TCP的速度控制方法必須使用不超過TCP資料流的頻寬。然而，這些方法常只使用低於TCP資料流的頻寬來保守的達到公眾公平性。在另一方面，為維持私有公平性，使用封包排程器來管理瓶頸路徑是一個常見的方法。但是, 這方法無法在使用者端的接取閘道器上管理呈現瓶頸狀態的下載路徑，因為他不能控制或排程那些在使用者端對面之ISP端閘道器等候的封包。 我們首先針對八個知名的速度控制方法，探討其為何無法恰巧使用與TCP相等的頻寬，也就是表現出TCP-equivalence的特性。接著我們提出了一個window-averaging rate control (WARC)方法。藉由只考慮固定區間內的TCP速度，使得WARC能夠更早的拋棄歷史封包遺失狀態，因而能表現出比過去方法較好的TCP-equivalence特性。最後，我們又提出了minimum-service first request scheduling (MSF-RS)的方法來解決封包排程器無法在使用者端管理下載路徑的私有公平性問題。MSF-RS藉由排程上行路徑請求以控制下行路徑回應的方式，來達到使用者為基礎的權重公平性，也就是無論一類別使用者數量多寡，都能確保高等級類別使用者獲得較多的頻寬。 模擬結果分別在非週期性封包遺失，低耦合度流量，雙狀態遺失，及突現性大量遺失四種狀態下，顯示出先前速度控制方法無法在TCP-equivalence情況下維持公眾公平性的原因，而分析及模擬結果也顯示WARC能藉由更快的加減速反應，來表現更好的TCP-equivalence及達到公眾公平性。最後分析模擬及實驗結果顯示MSF-RS能在使用者閘道器上提供以使用者為基礎的私有權重公平性，並縮短20~30%的使用者感受延遲時間。

Flows may compete for bandwidth to transmit packets. Public fairness should be maintained by the flows when they compete for the bandwidth in the Internet, while private fairness may be required when they do at a private access link which connects the intranet to the Internet. To maintain the public fairness, rate control schemes different from TCP should use no more bandwidth than TCP. However, these schemes often only use less bandwidth to conservatively maintain the fairness. On the other hand, for maintaining the private fairness, the usual solution is using a packet scheduler to manage bottleneck. Nevertheless, the solution fails to manage the downlink bottleneck at the user-side access gateway, since it cannot schedule the packets queued at the ISP-side gateway, opposite to the user-side one. This dissertation first investigates eight well-known rate control schemes to reveal why they cannot maintain the public fairness by using just the same bandwidth as TCP, i.e. being TCP-equivalent. Next, this dissertation proposes a window-averaging rate control (WARC) scheme. Considering the TCP rate only over a fixed interval leads WARC to forget the historical packet loss condition more quickly and thus perform better TCP-equivalence than other schemes. Finally, a minimum-service first request scheduling (MSF-RS) scheme is proposed to solve the private fairness problem which packet schedulers fail to manage downlink at the user-side gateway. MSF-RS schedules uplink requests to control downlink responses in order to provide user-based weighted fairness, i.e. ensure high-class users to get more bandwidth even more users belong to the high class. The simulation results under non-periodic losses, low-multiplexing, two-state losses, and bursty-losses reveal the causes that previous schemes cannot maintain public fairness with TCP-equivalence. Next, both analysis and simulation demonstrate that WARC does maintain the fairness and perform better TCP-equivalence by exhibiting the faster aggressive and responsive behaviors. Finally, the analysis, simulation and field trial exhibit that MSF-RS provides the user-based private weighted fairness while reducing 20~30% of user-perceived latency at the user-side gateway.