差異性服務網路中封包分類與訊務標示方法之討論

Abstract

差異性服務 (Diffserv) 網路架構提供網際網路服務品質保證(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。封包分類器（packet classifier）是位於邊緣路由器(edge router)，依據封包標頭內容來分配至不同的微訊務流(micro-flows)。然而當兩個或多個過濾器(filter)有相交集的時候，會有一個隱密不顯的過濾器衝突問題發生，這會使得封包分類器無法正確的處理封包，更進一步會招致安全性的問題。所以，需要一些過濾器衝突偵測的機制來解決這問題。 在另一方面，訊務調節器 (traffic conditioner) 是位於邊緣路由器 (edge router) 上，裡面包含著測量(metering)、標示（marking）、塑型(shaping)和規範(policing)等功能。其中，當封包要離開時，裡面的訊務標示器會依據測量得到的結果，給予封包標示符合規約（in- of-profile）或是不符合規約（out-of-profile） 。而在差異性服務網路的後續端點，將會這些標示內容和網路負載的狀況，來決定做出哪些相對應的動作來處理封包。然而傳統的訊務標示器有些缺點。第一、對微訊務流之間的不公平標示造成某些微訊務得不到應得的服務品質保證。第二、符合規約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。更有甚者，在新的一些擁有升級功能的標示機制當中，會出現一個不公平升等的問題，而這會使得原先高服務等級的訊務無法永遠比其他低服務等級的訊務接受到較高的服務等級。而這可能使得高服務等級的訊務有比較高的機率被丟棄的可能。因此在這篇論文中，我們先提出了一個增進式三元可位址化為基礎的封包分類器來偵測過濾器衝突及處理封包分類的問題。經由我們的方法，可以使得有發生衝突的過濾器和最佳符合的過濾器，都可以在一次記憶體存取時間得到。另外，一個新的訊務標示器-具有積極性的公平訊務標示器(FTM_AP)-在這裡被提了出來。這標示器可以修正傳統標示器中不恰當標示的問題。新的機制是以雙速率三色標示器 (TRTCM) 為基本架構來發展，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。當升級機制被啟動時，新的機制會考量封包在傳送端最原始被標示的顏色。而這樣子的設計會減低不公平升等的效應。藉由模擬結果我們可以觀察出FTM_AP的效能比TC_PFG與TRTCM優異。

The Differentiated Services (DiffServ; DS) architecture is proposed for providing current Internet with QoS guarantee. In DiffServ, the traffic is separated to several classes according to the service contracts, and each class is offered with different QoS guarantee. The packet classifier is an element located in the edge router to examine the packet header and dispatch it to the different micro-flows. However, an implicit problem, called filter conflict, would occur when two or more filters overlap. This problem would cause the classifier unable to handle the packet correctly; furthermore, it could incur the security problem. Thus, some filter conflict detection schemes are needed to resolve the problem. On the other hands, the traffic conditioner is an element located in the edge router, which includes the functions of metering, marking, shaping and policing. The traffic maker takes the responsibility to mark the packet as either in- or out-of-profile according the measuring result when it exits the traffic marker. The corresponding actions will be taken in the later DS nodes according to the condition of network and the marking result of packet. However, there are several drawbacks in traditional traffic marker. First, the unfair marking appears and certain micro-flows would not achieve the deserved QoS requirement. Second, if a connection passes through more than one DS domains, it would be more probable to be demoted and dropped. In advance, the current some marking algorithm with a promotion function would incur an unjust promotion of the traffic. This problem could make the higher-level traffic not be always served more likely than the other lower-level traffic; moreover, the high-level traffic would be more probable to be dropped in this mechanism. In this thesis, we propose the e_TCAM (enhanced TCAM)-based classifier to detect the filter conflict and classify the incoming packets. Through applying our scheme, no matter the conflicted filter and the best-matching filter can be found in one memory access time. Also, a new traffic marker called, FTM_AP (Fair Traffic Marker with Aggressive Promotion), is proposed to amend the inappropriate markings in traditional marking algorithms. The new scheme is based on TRTCM (Two Rate Three Color Marker) scheme and allocates 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 bandwidth available. When the promotion mechanism is enabled, the packets its original color at the source would be considered, and it could reduce the effect of the unjust promotion. Simulation results show that FTM_AP outperforms the TRTCM and TC_PFG.