在差異性服務網路中具有改善頻寬配置功能的訊務調節器

Abstract

差異性服務 (Diffserv) 網路架構具有提供現存網際網路可行服務品質保證(QoS guarantee)的能力，它將網路上的訊務依訂定的契約內容分為數個群組 (classes) 並對每一群組提供不同等級的服務品質保證。訊務調節器 (traffic conditioner) 是差異性服務架構中用來量測群組實際流速對應訊務文件 (traffic profile) 規範並作出標示封包等對應動作的元件，它位於邊緣路由器 (edge router) 上。 離開訊務調節器的封包將會被標示成符合文件 (in-of-profile) 或是不符文件 (out-of-profile)的封包，這些標示將會在後續的節點上依網路負載的不同而成為丟棄判斷的依據。 在傳統訊務調節器的架構中我們經常可以看到漏水桶法則 (leaky bucket mechanism) 的應用，然而這種訊務調節器卻有些缺點。第一、對微訊務 (micro-flows) 之間的不公平標示造成某些微訊務得不到應得的頻寬。第二、符合文件的封包數量會隨著經過的差異性服務領域 (DS domain)個數變多而減少。因此在這篇論文中，我們提出具有封包升級與公平性允許功能的訊務調節器 (TC_PFG) 和增強型的TC_PFG (eTC_PFG)。這些新的訊務調節器是以雙速率三色標示器 (TRTCM) 為基本架構來發展的，具有對微訊務公平分配頻寬的特性並可以透過封包升級充分利用現有頻寬。藉由模擬結果我們可以看見TC_PFG與eTC_PFG優於TRTCM且eTC_PFG優於TC_PFG的表現。

The Differentiated Services (DiffServ; DS) architecture is proposed for providing the practical QoS guarantee. In DiffServ, the Internet traffic is separated to several classes according to the contracts signed between customers and service providers. Each class is offered with different QoS guarantee. The traffic conditioner, an element located in the edge router, is used to measure the arrival flow of aggregate traffic against the traffic profile and takes corresponding actions such as marking packets based on the measuring result. Each packet will be marked as either in- or out-of-profile when it exits the traffic conditioner. The corresponding actions will be taken in the later DS nodes according to the condition of network and the mark of packet. The leaky bucket mechanism is a deterministic flow control network element that is usually used in traditional traffic conditioner. However, there are several drawbacks in traditional traffic conditioner. First, the unfair marking appears and certain micro-flows would not achieve the deserved QoS requirement. Second, if a connection through more DS domains, it would be more probable to be demoted and dropped. In this thesis, we propose the TC_PFG (Traffic Conditioner with Promotion and Fairness Guarantee) and eTC_PFG (enhanced TC_PFG) to amend the inappropriate markings in traditional traffic conditioners. The new schemes are based on TRTCM (Two Rate Three Color Marker) scheme. They allocate appropriate bandwidth to micro-flows to reduce the unfair distribution among micro-flows and improve the utilization by allowing promotion of packets when there is available bandwidth. Simulation results show that both TC_PFG and eTC_PFG outperform the TRTCM and eTC_PFG performs better than TC_PFG.