Basic Search / Detailed Display

Author: 吳穰恆
Jang-Heng Wu
Thesis Title: 利用Chrony軟體與分段測量技術的時脈偏移測量方法
A Multi-Segment Clock Skew Measurement Utilizing Time Synchronization Software Chrony
Advisor: 鄧惟中
Wei-Chung Teng
Committee: 林宗男
王勝德
卓政宏
沈上翔
Degree: 碩士
Master
Department: 電資學院 - 資訊工程系
Department of Computer Science and Information Engineering
Thesis Publication Year: 2019
Graduation Academic Year: 107
Language: 中文
Pages: 44
Keywords (in Chinese): 時脈偏移
Keywords (in other languages): Chrony
Reference times: Clicks: 163Downloads: 3
Share:
School Collection Retrieve National Library Collection Retrieve Error Report
  • 現今使用網路時間通訊協定(Network Time Protocol) 的校時軟體均有兩種校正時間的方式。當時間誤差大時會直接校正時間,也就是將客戶端系統時間直接調整為伺服器的時間,針對此狀況過去的研究已提出利用熵的時脈偏移測量方法來進行正確測量;而當時間誤差較小則校時軟體調整客戶端的時脈或分段調整時間來逐步達到正確的時間,這種校時模式耗時較長,而且會導致錯誤的時脈偏移測
    量值。由於現今硬體製造技術進步且大多數連網設備每24 小時即進行同步,因此大部分的情況下時間誤差均為後者的情形,因此本研究針對這種情況下的時脈偏移量測提出方法。
    本研究比較最常見的校時軟體ntp 與chrony,針對校時所需時間去做考量,測試了在相同時間差下,所需要的校正時間。另一方面,我們也觀察到chrony 伺服器搭配適當參數的情況下,時間偏移量的分佈圖會呈現階梯狀分布,也因此可以利用分段式演算法DROML(Dynamic Region of Offset Majority Locating) 測量時脈偏移。
    本研究貢獻在於透過研究校時軟體chrony,發展出不論校時前時間誤差為何,
    均可以在校時過程中測量時脈偏移的方法。相較於未校時的時脈偏移值,校時過
    程中的測量誤差均不高於3ppm。


    The synchronization software over NTP (Network Time Protocol) supports two approaches of time synchronization. When the time difference between client and tim server is larger than some threshold, the system time of client will be directly set to the time of server site; Otherwise, the time synchronization software slightly altered the time or clock ticking rate to eliminate the amount of offset gradually. Entropy-based approaches are able to provide precise measurement for the former cases, but the measured clock skews in the later cases was never correct, and unfortunately most time synchronization belongs to the later cases. Therefore, this work aims at solving this issue.
    We studied the most common two time synchronization software ntp and chrony,
    including their patterns in later cases and the amount of time required upon the same amount of time difference. We observed that the scatter diagram of time offset during time chronization process become a series of cascade when chrony is used with appropriate parameters. The kind of pattern can be correctly solved by algorithm supporting multisegment measurement like DROML (Dynamic Region of Offset Majority Locating).
    The contribution of this work is to develop an approach based on chrony such that the clock skew is still measurable during time chronization process. Comparing to the normal condition, the observed errors of the proposed approach are bound to 3 ppm.

    目錄 論文摘要 Abstract 誌謝 目錄 圖目錄 表目錄 1 緒論 1.1 研究背景 1.2 研究動機與目的 1.3 論文架構 2 背景知識與相關研究 2.1 時脈偏移定義 2.2 時脈偏移測量方法 2.2.1 基於霍氏轉換的時脈偏移測量方法 2.2.2 改良的霍氏轉換方法 2.2.3 基於霍氏轉換法的動態鎖定時脈偏移區間的測量方法 2.2.4 利用熵的時脈偏移測量方法 2.3 介紹校時軟體 2.3.1 ntpd 2.3.2 chronyd 3 研究方法 3.1 校時參數設定 3.2 方法流程 4 實驗結果與分析 4.1 實驗環境 4.2 實驗設計 4.2.1 前期實驗: 求出理想參數 4.2.2 實驗一: 比較使用此方法前後時脈偏移之差異 4.2.3 實驗二: 驗證校時期間測量方法之有效性 4.3 實驗結果比較 4.3.1 前期實驗結果 4.3.2 實驗一結果 4.3.3 實驗二結果 5 結論 參考文獻

    [1] T. Kohno, A. Broido, and K. C. Claffy, “Remote physical device fingerprinting,”
    IEEE Transactions on Dependable and Secure Computing, vol. 2, pp. 93–108, 2005.
    [2] S. Murdoch, “Hot or not: Revealing hidden services by their clock skew,” in Proceedings
    of the 13th ACM conference on Computer and communications security,
    pp. 27–36, 2006.
    [3] S. Zander and S. Murdoch, “An Improved Clock-skew Measurement Technique for
    Revealing Hidden Services.,” in USENIX Security Symposium, pp. 211–225, 2008.
    [4] D. J. Huang, K. T. Yang, C. C. Ni, W. C. Teng, T. R. Hsiang, and Y. J. Lee, “Clock
    skew based client device identification in cloud environments,” in Proceedings -
    International Conference on Advanced Information Networking and Applications,
    AINA, pp. 526–533, 2012.
    [5] 鄭理介, “基於時脈偏移的可攜式裝置識別技術,” 碩士論文, 國立台灣科技大
    學,2013.
    [6] S. B. Moon, P. Skelly, and D. Towsley, “Estimation and removal of clock skew from
    network delay measurements,” in Proceedings - IEEE INFOCOM, pp. 11–15, 1999.
    [7] K. Oka Saputra, W. C. Teng, and T. H. Chen, “Hough Transform-Based Clock Skew
    Measurement over Network,” IEEE Transactions on Instrumentation and Measurement,
    vol. 64, no. 12, pp. 3209–3216, 2015.
    [8] K. Oka Saputra, W. C. Teng, and T. Nara, “Hough transform-based clock skew measurement
    by dynamically locating the region of offset majority,” in IEICE Transactions
    on Information and Systems, 2016.
    [9] 何建德, “一個利用熵的時脈偏移測量方法,” 碩士論文, 國立台灣科技大學,
    2016.
    [10] D. J. Huang, W. C. Teng, C. Y. Wang, H. Y. Huang, and J. M. Hellerstein, “Clock
    skew based node identification in wireless sensor networks,” in GLOBECOM - IEEE
    Global Telecommunications Conference, pp. 1–5, 2008.
    [11] V. Paxson, “On calibrating measurements of packet transit times,” ACM SIGMETRICS
    Performance Evaluation Review, vol. 26, no. 1, pp. 11–21, 1998.
    [12] P. V. C. Hough, “Method and means for recognizing complex patterns,” US Patent
    3,069,654, 1962.
    [13] R. O. Duda and P. E. Hart, “Use of the Hough transformation to detect lines and
    curves in pictures,” Communications of the ACM, 1972.
    [14] 楊祐齊, “一個改良的基於霍式轉換時脈偏移之研究,” 碩士論文, 國立台灣科技
    大學,2015.
    [15] C. E. Shannon, “A mathematical theory of communication,” ACM SIGMOBILE Mobile
    Computing and Communications Review, 2001.
    [16] “ntpd - network time protocol (ntp) daemon.” https://www.eecis.udel.edu/
    ~mills/ntp/html/ntpd.html. (Accessed on 07/25/2018).
    [17] “chrony –introduction.” https://chrony.tuxfamily.org/index.html. (Accessed
    on 07/25/2018).

    QR CODE