一個網路校時系統之標準時間伺服器與追蹤方法設計製作

Abstract

本文旨在探索並研製一套完整的自動化標準時間系統（從使用者到伺服端），在解決一封閉區域網路內之電腦系統與國家標準時間同步的問題。對於NTP（Network Time Protocol）協定之網際網路校時而言，可能會發生兩種主要情況：一為校時不準確；即由於路徑延遲效應，產生不穩定的校時。二為網路安全受威脅；即開放式的網際網路連接，易受駭客的攻擊。另外也可能因加裝防火牆而關閉NTP埠阻擋校時。本研製含： 1. 撥接校時伺服系統(Taiwan's Computer Time System, TCTS)：藉由電話迴路，開發具折返(Loop-back)模式之撥接式校時系統，即時補償有關傳輸路徑延遲問題，使校時準確度最佳可達到±0.5毫秒。本文將深入探討折返模式之原理，實際硬體製作及軟體設計。 2. 標準時間追蹤方法(Standard-Time Tracking Scheme, STTS)：除了提出一實現準確時間(絕對時間)的追蹤方法外，並著重使用硬體描述語言(Hardware Description Language, HDL)及複雜型可規劃式邏輯晶片(Complex Programmable Logic Device, CPLD)，來發展自動補償(根據給予的演算法)因時基頻率偏移所累積時間差的智慧型計時器(Intelligence Real-Time Clock, IRTC)，最終完成一顆經功能及時序驗證完成的IC(Integrated Circuit)設計。 3. 設置一可應用的網路時間伺服系統：致力於在Linux作業系統環境下，建立一個結合TCTS及STTS的本地第一階NTP時間伺服器；亦即構成一套擁有獨立外部參考時間源的網路時間伺服系統。最後將驗證本系統之準確度達到預期±3毫秒範圍，這準確度應用在目前的網路架構下校時，已綽綽有餘。

In this thesis, we developed a standard time-server(TCTS) and tracking scheme (STTS) for a network time system that deals with Network Time Protocol (NTP). The purpose of this effort was to solve the synchronization problems for computer time system in the isolated local area network. In practice we quoted various theorems and coordinated some techniques such as a digital system on a programmable chip (SOPC) and the microprocessor to support this study, which result in better accuracy and stability. In the TCTS, we developed a time system with loop-back mode that can access to national standard time by telephone line with accuracy approaching ±0.5 millisecond (ms). In the STTS, we used hardware describe languages (HDL) and a complex programmable logic device (CPLD) to develop an intelligence real-time clock (IRTC) IC (Integrated Circuit), which automatically self-compensated its time error according to the given algorithms. In the last, this IC has been verified regarding its functions and timing through the electronic design automation (EDA) tools. Finally, we configured a stand-alone NTP time-server under Linux OS, with external TCTS+STTS. Then we built a test environment to collect its data in practice. To analyze these data, we verified this system with accuracy reaching our expectation ±3 ms. This performance is good enough for the modern NTP users in local area network.