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Author: 孫國仁
Guo-Jen Sun
Thesis Title: 網路時鐘偏斜測量中虛線現象之研究
A Study of Dotted-Line Phenomena for Clock Skew Measurement over Network
Advisor: 鄧惟中
Wei-Chung Teng
Committee: 項天瑞
Tien-Ruey Hsiang
金台齡
Tai-Lin Chin
Degree: 碩士
Master
Department: 電資學院 - 資訊工程系
Department of Computer Science and Information Engineering
Thesis Publication Year: 2016
Graduation Academic Year: 104
Language: 中文
Pages: 55
Keywords (in Chinese): 虛線現象時鐘偏斜時間精度
Keywords (in other languages): Dotted Line, Clock Skew, Time Resolution
Reference times: Clicks: 236Downloads: 8
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本研究探討因網路接收端設備時間精度較發送端設備的精度低而生成之虛線(dotted lines)現象,及其對於測量時鐘偏斜的影響。透過網路兩端之時戳接收裝置與發送裝置,設定時間精度和傳輸時間戳記封包,觀察不同時間精度與虛線特性,以及是否影響時鐘偏斜之估算。
本研究經由TCP/IP之UDP傳輸協定,於Wi-Fi無線網路中以不同發送間隔傳輸10萬筆時間戳記封包,再將封包接收時間與偏移量等資訊轉換至散佈圖而求得虛線。從所蒐集到的偏移量中觀察可發現,虛線現象的生成與時間精度確實有關聯性,不同時間精度直接影響虛線長度、斜率和虛線間距,以及虛線呈現於散佈圖上之排列規律。時間精度在接收裝置設定為15.6 ms,發送裝置為1 ms時,虛線長度為9、虛線斜率為-0.0016,虛線間距為0.016 s,循此規律循環排列於散佈圖。應用此特性,則可以濾除離群資料點,再以Quick Piecewise Minimum Algorithm和Linear Regression Method等演算法估算所有時間精度條件下之時鐘偏斜值,誤差皆在1 ppm以內。


With the rise of cloud computing concepts, the popularization of portable devices, and the development of the Internet of Things, a lot of discussion on device identification regarding personal information privacy and power consumption has surfaced. Different devices have distinct clock skew, and the clock skew estimated by the timestamp taken from network data packets can be used as a fingerprint for device identification. Adjustable time resolution provides the option for different levels of performance, and is useful for finding the optimal balance between energy efficiency and performance. This study investigated the dotted lines phenomenon caused by time resolution and its effects on measuring clock skew. Using the timestamp from transmitting and receiving devices on both ends of the network, the time resolution can be set and sent with the timestamp packet to observe the dotted lines characteristics with different time resolutions and its impact on the clock skew estimation can be determined.
The dotted lines phenomenon is reflected in the information such as the time received and time offset shown on a scatter diagram that is created when one million timestamp packages sent at different time intervals via the Wi-Fi network using the transmission protocol UDP in TCP/IP. As shown from the results, it was observed that there is a correlation between the formation of the dotted lines phenomenon and time resolution. Time resolution directly affects the length, slope, and intervals of the dotted lines as well as the sequence pattern of the scatter diagram. When the time resolution was set to 15.6 ms on the receiving device and 1 ms on the transmitting device, the length of a dotted line was 9, with a slope of -0.0016, and its interval was 0.016 seconds. The data were scattered following this trend. Using these characteristics to filter out the outlier point, the Quick Piecewise Minimum Algorithm and the Linear Regression Method were employed to estimate the clock slew values under each time resolution with an accuracy of within 1 ppm.

摘要 i Abstract ii 誌謝 iii 目錄 iv 圖目錄 vi 表目錄 vii 第1章 緒論 1 1.1研究背景 1 1.2研究動機與目的 2 1.3論文架構 3 第2章 背景知識與相關研究 4 2.1時鐘與時鐘偏斜 4 2.2時鐘偏斜與裝置辨識技術 5 2.3時鐘偏斜測量方法 6 2.3.1 Quick Piecewise Minimum Algorithm (QPM) 7 2.3.2 Linear Regression Method (LRM) 8 2.4時間精度(Time Resolution) 8 2.5虛線現象判斷法 11 第3章 虛線的性質 13 3.1時間精度與虛線現象關聯性 13 3.2虛線的長度、斜率和間距 17 3.2.1虛線長度 18 3.2.2虛線斜率 19 3.3.3虛線間距 20 3.3虛線分群法 21 3.4利用虛線特性濾除離群點 24 第4章 利用虛線進行時鐘偏斜測量 25 4.1時戳資料傳輸環境 25 4.2時戳資料傳輸設定 26 4.3時戳資料結果與分析 27 4.3.1實際虛線現象與理論特性之比較 28 4.3.2虛線現象與時鐘偏斜的影響 30 4.3.3時戳封包傳輸間隔與虛線斜率之比較 33 4.3.4時戳封包傳輸間隔與虛線長度之比較 34 4.3.5時戳封包傳輸間隔與虛線資料點個數之比較 35 4.3.6時戳封包傳輸間隔與虛線間距之比較 36 4.3.7不同時間精度與時鐘偏斜值之比較 37 4.3.8不同時間精度與虛線斜率之比較 38 4.3.9不同時間精度與虛線長度之比較 39 4.3.10不同時間精度與虛線間距之比較 40 4.3.11虛線特性、時鐘偏斜、時間精度與時戳間隔整體分析 41 第5章 結論與未來研究方向 43 5.1結論 43 5.2未來研究方向 43 參考文獻 44

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