一次差分可攜式網路延遲量測方法之設計與實現

Abstract

摘要 網路系統中之點對點延遲資訊對於各種在電信、電力、自動化以及財務資訊系統領域中具有 QoS (Quality of Service) 要求的應用或服務都相當重要。欲達成各式應用服務的品質要求,更精確的網路延遲時間量測方法則是關鍵。此外，如何在不影響一個運作中網路系統的前提，即時並有彈性的對網路中任意線段或是節點進行高精度知延遲資訊的量測亦是刻不容緩需要解決的需求。 對於無法量測或觀察到的資訊或是變化，吾人是不可能對其進行改善以及控制。因此，在本論文中基於上述的觀點，將主要的量測方法設計考量專注在量測精度的提升。在符合奈妙精度的要求下，提高量測方法的彈性及方便性。最後，在將提出的高精度點對點延遲量測展示於具有前瞻性的網路應用。 本論文提出一次差分可攜式點對點延遲量測方法 (SD-PELM)。一次差分之量測演算可以針對由底層硬體電路以及同步傳輸不對稱性造成的時間延遲偏差進行修正，使得量測結果之不準確度可維持在十倍奈秒等級以下。同時該提出量測方法以可滿足在不影響各種網路應用服務運作前提下，即時並富有伸縮彈性地量測網路系統中任意節點延遲資訊的需求。 本論文同時透過採用高精確量測方法 SD-PELM 展示相關前瞻性的量測應用。第一個應用是網路通訊設備之高精度量測。本論文針對兩台封包轉送之延遲效能不同的網路交換器進行實測，並從量測結果驗證所提出之量測方法可以精確的獲得其設備的封包轉送延遲資訊。第二個應用是流量指標器。該指標器可以精確的分辨所量測節點之間目前的即時流量資訊，其流量的辨識能力可大至數百 Mbps、小至數 Mbps。

Abstract The end-to-end latency information is valuable to many networked applications and services, such as telecommunication, power utility, automation, and financial systems, that demand stringent Qualify of Service (QoS). To meet the performance requirements of a diverse set of applications and services, there are strong demands to achieve more accurate latency measurement with more precise resolution than ever before. Additionally, it is critical that such timing information can be flexibly and robustly measured without negatively affecting the network operations. It is reasonable that people can control and improve something only if they can measure or observe it. In this dissertation, we investigate the precision issue of end-to- end latency measurement in Ethernet networks, and design high precision measurement solutions to achieve flexible and robust measurements. We then demonstrate few promising applications that utilize the high precision latency information. Specifically, this dissertation proposes the approach of Single-Difference Portable End-to-end Latency Measurement (SD-PELM). The SD calculation in the proposed approach can eliminate major elements of the offset caused by the lower- layer hardware circuits and the effect of synchronization between measured nodes so that the measured latency can be precise in the resolution of nanoseconds. In addition to the improved measurement precision, PELM facilitates the feature of measuring any arbitrary pair of nodes in an Ethernet network without negatively impacting the operations of the measured network. SD-PELM can be regarded as a plug-and-play latency meter. The dissertation demonstrates several promising measurement applications that utilize the proposed SD-PELM. The first application is the precise switch measurement. The result shows that the latency of switch ranging from microsecond to nanosecond can be measured for further uses. The second application is the traffic indicator, which can differentiate the traffic loads between Probing Points (PPs). The traffic indicator demonstrates the capability of SD-PELM to clearly identify traffic loads ranging from few Mbps to hundreds of Mbps.