本文介绍Network Time Protocol (NTP)的基本概念及其在Windows Server 2003上的配置方法，并提供了一个使用C#实现的NTP客户端示例代码。
Network Time Protocol（NTP）是用来使计算机时间同步化的一种协议，它可以使计算机对其服务器或时钟源（如石英钟，GPS等等)做同步化，它可以提供高精准 度的时间校正（LAN上与标准间差小于1毫秒，WAN上几十毫秒），且可介由加密确认的方式来防止恶毒的协议攻击。
NTP采用C/S结构，Server端作为时间来源，可以是原子钟、天文台、卫星，也可以从Internet上获取；而在我们的局域网内，则可以配置一个服务器，将其硬件时间作为时间源来提供服务；我在网上搜索了一下，大部分关于NTP服务的文章都是基于Linux的，提到windows server系列操作系统的不是很多，不过还是有很实用的内容；总结下来，其实要在windows server 2003上配置NTP服务是一件很简单的事情，如果该服务器是域控制器（DC），则已经默认启动了一个叫做win32time的服务，这个服务就是我们的NTPServer；如果不是域控制器，只需要修改注册表HKEY_LOCAL_MACHINE>>SYSTEM>>CurrentControlSet>>Services>>W32Time>>TimeProviders>>NtpServer下的Enabled为1（true）即可强制其宣布自身为可靠的时间源以启动win32time服务。
Client端通过主动连接有效的Server端即可同步本地时间；以下是我在CodeProject上找到的有关NTPClient在C#下实现的代码（原帖地址）：
NTPClient
/*
* NTPClient
* Copyright (C)2001 Valer BOCAN <vbocan@dataman.ro>
* Last modified: June 29, 2001
* All Rights Reserved
*
* This code is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY, without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*
* To fully understand the concepts used herein, I strongly
* recommend that you read the RFC 2030.
*
* NOTE: This example is intended to be compiled with Visual Studio .NET Beta 2
*/
namespace TimeSync {
using System;
using System.Net;
using System.Net.Sockets;
using System.Runtime.InteropServices;
// Leap indicator field values
public enum _LeapIndicator {
NoWarning, // 0 - No warning
LastMinute61, // 1 - Last minute has 61 seconds
LastMinute59, // 2 - Last minute has 59 seconds
Alarm // 3 - Alarm condition (clock not synchronized)
}
//Mode field values
public enum _Mode {
SymmetricActive, // 1 - Symmetric active
SymmetricPassive, // 2 - Symmetric pasive
Client, // 3 - Client
Server, // 4 - Server
Broadcast, // 5 - Broadcast
Unknown // 0, 6, 7 - Reserved
}
// Stratum field values
public enum _Stratum {
Unspecified, // 0 - unspecified or unavailable
PrimaryReference, // 1 - primary reference (e.g. radio-clock)
SecondaryReference, // 2-15 - secondary reference (via NTP or SNTP)
Reserved // 16-255 - reserved
}
/// <summary>
/// NTPClient is a C# class designed to connect to time servers on the Internet.
/// The implementation of the protocol is based on the RFC 2030.
///
/// Public class members:
///
/// LeapIndicator - Warns of an impending leap second to be inserted/deleted in the last
/// minute of the current day. (See the _LeapIndicator enum)
///
/// VersionNumber - Version number of the protocol (3 or 4).
///
/// Mode - Returns mode. (See the _Mode enum)
///
/// Stratum - Stratum of the clock. (See the _Stratum enum)
///
/// PollInterval - Maximum interval between successive messages.
///
/// Precision - Precision of the clock.
///
/// RootDelay - Round trip time to the primary reference source.
///
/// RootDispersion - Nominal error relative to the primary reference source.
///
/// ReferenceID - Reference identifier (either a 4 character string or an IP address).
///
/// ReferenceTimestamp - The time at which the clock was last set or corrected.
///
/// OriginateTimestamp - The time at which the request departed the client for the server.
///
/// ReceiveTimestamp - The time at which the request arrived at the server.
///
/// Transmit Timestamp - The time at which the reply departed the server for client.
///
/// RoundTripDelay - The time between the departure of request and arrival of reply.
///
/// LocalClockOffset - The offset of the local clock relative to the primary reference
/// source.
///
/// Initialize - Sets up data structure and prepares for connection.
///
/// Connect - Connects to the time server and populates the data structure.
/// It can also set the system time.
///
/// IsResponseValid - Returns true if received data is valid and if comes from
/// a NTP-compliant time server.
///
/// ToString - Returns a string representation of the object.
///
/// -----------------------------------------------------------------------------
/// Structure of the standard NTP header (as described in RFC 2030)
/// 1 2 3
/// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// |LI | VN |Mode | Stratum | Poll | Precision |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | Root Delay |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | Root Dispersion |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | Reference Identifier |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | |
/// | Reference Timestamp (64) |
/// | |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | |
/// | Originate Timestamp (64) |
/// | |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | |
/// | Receive Timestamp (64) |
/// | |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | |
/// | Transmit Timestamp (64) |
/// | |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | Key Identifier (optional) (32) |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | |
/// | |
/// | Message Digest (optional) (128) |
/// | |
/// | |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
///
/// -----------------------------------------------------------------------------
///
/// NTP Timestamp Format (as described in RFC 2030)
/// 1 2 3
/// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | Seconds |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/// | Seconds Fraction (0-padded) |
/// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
///
/// </summary>
public class NTPClient {
// NTP Data Structure Length
private const byte NTPDataLength = 48;
// NTP Data Structure (as described in RFC 2030)
byte[] NTPData = new byte[NTPDataLength];
// Offset constants for timestamps in the data structure
private const byte offReferenceID = 12;
private const byte offReferenceTimestamp = 16;
private const byte offOriginateTimestamp = 24;
private const byte offReceiveTimestamp = 32;
private const byte offTransmitTimestamp = 40;
// Leap Indicator
public _LeapIndicator LeapIndicator {
get {
// Isolate the two most significant bits
byte val = (byte)(NTPData[0] >> 6);
switch (val) {
case 0: return _LeapIndicator.NoWarning;
case 1: return _LeapIndicator.LastMinute61;
case 2: return _LeapIndicator.LastMinute59;
case 3: goto default;
default:
return _LeapIndicator.Alarm;
}
}
}
// Version Number
public byte VersionNumber {
get {
// Isolate bits 3 - 5
byte val = (byte)((NTPData[0] & 0x38) >> 3);
return val;
}
}
// Mode
public _Mode Mode {
get {
// Isolate bits 0 - 3
byte val = (byte)(NTPData[0] & 0x7);
switch (val) {
case 0: goto default;
case 6: goto default;
case 7: goto default;
default:
return _Mode.Unknown;
case 1:
return _Mode.SymmetricActive;
case 2:
return _Mode.SymmetricPassive;
case 3:
return _Mode.Client;
case 4:
return _Mode.Server;
case 5:
return _Mode.Broadcast;
}
}
}
// Stratum
public _Stratum Stratum {
get {
byte val = (byte)NTPData[1];
if (val == 0) return _Stratum.Unspecified;
else
if (val == 1) return _Stratum.PrimaryReference;
else
if (val <= 15) return _Stratum.SecondaryReference;
else
return _Stratum.Reserved;
}
}
// Poll Interval
public uint PollInterval {
get {
return (uint)Math.Round(Math.Pow(2, NTPData[2]));
}
}
// Precision (in milliseconds)
public double Precision {
get {
return (1000 * Math.Pow(2, NTPData[3]));
}
}
// Root Delay (in milliseconds)
public double RootDelay {
get {
int temp = 0;
temp = 256 * (256 * (256 * NTPData[4] + NTPData[5]) + NTPData[6]) + NTPData[7];
return 1000 * (((double)temp) / 0x10000);
}
}
// Root Dispersion (in milliseconds)
public double RootDispersion {
get {
int temp = 0;
temp = 256 * (256 * (256 * NTPData[8] + NTPData[9]) + NTPData[10]) + NTPData[11];
return 1000 * (((double)temp) / 0x10000);
}
}
// Reference Identifier
public string ReferenceID {
get {
string val = "";
switch (Stratum) {
case _Stratum.Unspecified:
goto case _Stratum.PrimaryReference;
case _Stratum.PrimaryReference:
val += (char)NTPData[offReferenceID + 0];
val += (char)NTPData[offReferenceID + 1];
val += (char)NTPData[offReferenceID + 2];
val += (char)NTPData[offReferenceID + 3];
break;
case _Stratum.SecondaryReference:
switch (VersionNumber) {
case 3: // Version 3, Reference ID is an IPv4 address
string Address = NTPData[offReferenceID + 0].ToString() + "." +
NTPData[offReferenceID + 1].ToString() + "." +
NTPData[offReferenceID + 2].ToString() + "." +
NTPData[offReferenceID + 3].ToString();
try {
IPHostEntry Host = Dns.GetHostByAddress(Address);
val = Host.HostName + " (" + Address + ")";
} catch (Exception) {
val = "N/A";
}
break;
case 4: // Version 4, Reference ID is the timestamp of last update
DateTime time = ComputeDate(GetMilliSeconds(offReferenceID));
// Take care of the time zone
TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
val = (time + offspan).ToString();
break;
default:
val = "N/A";
break;
}
break;
}
return val;
}
}
// Reference Timestamp
public DateTime ReferenceTimestamp {
get {
DateTime time = ComputeDate(GetMilliSeconds(offReferenceTimestamp));
// Take care of the time zone
TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
return time + offspan;
}
}
// Originate Timestamp
public DateTime OriginateTimestamp {
get {
return ComputeDate(GetMilliSeconds(offOriginateTimestamp));
}
}
// Receive Timestamp
public DateTime ReceiveTimestamp {
get {
DateTime time = ComputeDate(GetMilliSeconds(offReceiveTimestamp));
// Take care of the time zone
TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
return time + offspan;
}
}
// Transmit Timestamp
public DateTime TransmitTimestamp {
get {
DateTime time = ComputeDate(GetMilliSeconds(offTransmitTimestamp));
// Take care of the time zone
TimeSpan offspan = TimeZone.CurrentTimeZone.GetUtcOffset(DateTime.Now);
return time + offspan;
}
set {
SetDate(offTransmitTimestamp, value);
}
}
// Reception Timestamp
public DateTime ReceptionTimestamp;
// Round trip delay (in milliseconds)
public int RoundTripDelay {
get {
TimeSpan span = (ReceiveTimestamp - OriginateTimestamp) + (ReceptionTimestamp - TransmitTimestamp);
return (int)span.TotalMilliseconds;
}
}
// Local clock offset (in milliseconds)
public int LocalClockOffset {
get {
TimeSpan span = (ReceiveTimestamp - OriginateTimestamp) - (ReceptionTimestamp - TransmitTimestamp);
return (int)(span.TotalMilliseconds / 2);
}
}
// Compute date, given the number of milliseconds since January 1, 1900
private DateTime ComputeDate(ulong milliseconds) {
TimeSpan span = TimeSpan.FromMilliseconds((double)milliseconds);
DateTime time = new DateTime(1900, 1, 1);
time += span;
return time;
}
// Compute the number of milliseconds, given the offset of a 8-byte array
private ulong GetMilliSeconds(byte offset) {
ulong intpart = 0, fractpart = 0;
for (int i = 0; i <= 3; i++) {
intpart = 256 * intpart + NTPData[offset + i];
}
for (int i = 4; i <= 7; i++) {
fractpart = 256 * fractpart + NTPData[offset + i];
}
ulong milliseconds = intpart * 1000 + (fractpart * 1000) / 0x100000000L;
return milliseconds;
}
// Compute the 8-byte array, given the date
private void SetDate(byte offset, DateTime date) {
ulong intpart = 0, fractpart = 0;
DateTime StartOfCentury = new DateTime(1900, 1, 1, 0, 0, 0); // January 1, 1900 12:00 AM
ulong milliseconds = (ulong)(date - StartOfCentury).TotalMilliseconds;
intpart = milliseconds / 1000;
fractpart = ((milliseconds % 1000) * 0x100000000L) / 1000;
ulong temp = intpart;
for (int i = 3; i >= 0; i--) {
NTPData[offset + i] = (byte)(temp % 256);
temp = temp / 256;
}
temp = fractpart;
for (int i = 7; i >= 4; i--) {
NTPData[offset + i] = (byte)(temp % 256);
temp = temp / 256;
}
}
// Initialize the NTPClient data
private void Initialize() {
// Set version number to 4 and Mode to 3 (client)
NTPData[0] = 0x1B;
// Initialize all other fields with 0
for (int i = 1; i < 48; i++) {
NTPData[i] = 0;
}
// Initialize the transmit timestamp
TransmitTimestamp = DateTime.Now;
}
public NTPClient(string host) {
TimeServer = host;
}
// Connect to the time server and update system time
public void Connect(bool UpdateSystemTime) {
try {
// Resolve server address
IPHostEntry hostadd = Dns.Resolve(TimeServer);
IPEndPoint EPhost = new IPEndPoint(hostadd.AddressList[0], 123);
//Connect the time server
UdpClient TimeSocket = new UdpClient();
TimeSocket.Connect(EPhost);
// Initialize data structure
Initialize();
TimeSocket.Send(NTPData, NTPData.Length);
NTPData = TimeSocket.Receive(ref EPhost);
if (!IsResponseValid()) {
throw new Exception("Invalid response from " + TimeServer);
}
ReceptionTimestamp = DateTime.Now;
} catch (SocketException e) {
throw new Exception(e.Message);
}
// Update system time
if (UpdateSystemTime) {
SetTime();
}
}
// Check if the response from server is valid
public bool IsResponseValid() {
if (NTPData.Length < NTPDataLength || Mode != _Mode.Server) {
return false;
} else {
return true;
}
}
// Converts the object to string
public override string ToString() {
string str;
str = "Leap Indicator: ";
switch (LeapIndicator) {
case _LeapIndicator.NoWarning:
str += "No warning";
break;
case _LeapIndicator.LastMinute61:
str += "Last minute has 61 seconds";
break;
case _LeapIndicator.LastMinute59:
str += "Last minute has 59 seconds";
break;
case _LeapIndicator.Alarm:
str += "Alarm Condition (clock not synchronized)";
break;
}
str += "\r\nVersion number: " + VersionNumber.ToString() + "\r\n";
str += "Mode: ";
switch (Mode) {
case _Mode.Unknown:
str += "Unknown";
break;
case _Mode.SymmetricActive:
str += "Symmetric Active";
break;
case _Mode.SymmetricPassive:
str += "Symmetric Pasive";
break;
case _Mode.Client:
str += "Client";
break;
case _Mode.Server:
str += "Server";
break;
case _Mode.Broadcast:
str += "Broadcast";
break;
}
str += "\r\nStratum: ";
switch (Stratum) {
case _Stratum.Unspecified:
case _Stratum.Reserved:
str += "Unspecified";
break;
case _Stratum.PrimaryReference:
str += "Primary Reference";
break;
case _Stratum.SecondaryReference:
str += "Secondary Reference";
break;
}
str += "\r\nLocal time: " + TransmitTimestamp.ToString();
str += "\r\nPrecision: " + Precision.ToString() + " ms";
str += "\r\nPoll Interval: " + PollInterval.ToString() + " s";
str += "\r\nReference ID: " + ReferenceID.ToString();
str += "\r\nRoot Dispersion: " + RootDispersion.ToString() + " ms";
str += "\r\nRound Trip Delay: " + RoundTripDelay.ToString() + " ms";
str += "\r\nLocal Clock Offset: " + LocalClockOffset.ToString() + " ms";
str += "\r\n";
return str;
}
// SYSTEMTIME structure used by SetSystemTime
[StructLayoutAttribute(LayoutKind.Sequential)]
private struct SYSTEMTIME {
public short year;
public short month;
public short dayOfWeek;
public short day;
public short hour;
public short minute;
public short second;
public short milliseconds;
}
[DllImport("kernel32.dll")]
static extern bool SetLocalTime(ref SYSTEMTIME time);
// Set system time according to transmit timestamp
private void SetTime() {
SYSTEMTIME st;
DateTime trts = TransmitTimestamp;
st.year = (short)trts.Year;
st.month = (short)trts.Month;
st.dayOfWeek = (short)trts.DayOfWeek;
st.day = (short)trts.Day;
st.hour = (short)trts.Hour;
st.minute = (short)trts.Minute;
st.second = (short)trts.Second;
st.milliseconds = (short)trts.Millisecond;
SetLocalTime(ref st);
}
// The URL of the time server we're connecting to
private string TimeServer;
}
}
对NTPClient的调用
using
System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using TimeSync;
using System.Configuration;
namespace CommandLine {
class Program {
static void Main( string [] args) {
timeServer = ConfigurationManager.AppSettings[ " NTPServer " ];
Console.WriteLine( " Connecting to:{0} " , timeServer);
try {
client = new NTPClient(timeServer);
client.Connect( true );
Console.Write(client.ToString());
} catch (Exception ex) {
Console.WriteLine(ex);
}
Console.WriteLine( " == End == " );
Console.ReadKey();
}
private static string timeServer;
private static NTPClient client;
}
}
using System.Collections.Generic;
using System.Linq;
using System.Text;
using TimeSync;
using System.Configuration;
namespace CommandLine {
class Program {
static void Main( string [] args) {
timeServer = ConfigurationManager.AppSettings[ " NTPServer " ];
Console.WriteLine( " Connecting to:{0} " , timeServer);
try {
client = new NTPClient(timeServer);
client.Connect( true );
Console.Write(client.ToString());
} catch (Exception ex) {
Console.WriteLine(ex);
}
Console.WriteLine( " == End == " );
Console.ReadKey();
}
private static string timeServer;
private static NTPClient client;
}
}
配置文件：
<?
xml version
=
"
1.0
"
encoding
=
"
utf-8
"
?>
< configuration >
< appSettings >
< add key = " NTPServer " value = " 192.168.16.101 " />
</ appSettings >
</ configuration >
< configuration >
< appSettings >
< add key = " NTPServer " value = " 192.168.16.101 " />
</ appSettings >
</ configuration >
运行结果：
对于大型局域网，可以使用多台服务器在逻辑上形成阶梯式的架构相互连接，对服务器进行分层（Stratum），Stratum-1的时间服务器是整个系统的基础，Stratum-2从Stratum-1获取时间，Stratum-3从Stratum-2获取时间，以此类推，Stratum的总数限制在15以内；由于我目前只是使用单一服务器提供整个局域网内的时间服务，因此服务端配置比较简单，而层的配置则相对复杂，还有很多需要研究的地方。
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