C#을 이용한 NTP Service

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.IO;

using System.Net;

using System.Net.Sockets;

namespace NTPService_Time

{

    /// <summary>

    /// Static class to receive the time from a NTP server.

    /// </summary>

    public static class NtpClient

    {

        /// <summary>

        /// Gets the current DateTime from time-a.nist.gov.

        /// </summary>

        /// <returns>A DateTime containing the current time.</returns>

        public static DateTime GetNetworkTime()

        {

            return GetNetworkTime("time.windows.com"); // time-a.nist.gov

        }

        /// <summary>

        /// Gets the current DateTime from <paramref name="ntpServer"/>.

        /// </summary>

        /// <param name="ntpServer">The hostname of the NTP server.</param>

        /// <returns>A DateTime containing the current time.</returns>

        public static DateTime GetNetworkTime(string ntpServer)

        {

            IPAddress[] address = Dns.GetHostEntry(ntpServer).AddressList;

            if (address == null || address.Length == 0)

                throw new ArgumentException("Could not resolve ip address from '" + ntpServer + "'.", "ntpServer");

            IPEndPoint ep = new IPEndPoint(address[0], 123);

            return GetNetworkTime(ep);

        }

        /// <summary>

        /// Gets the current DateTime form <paramref name="ep"/> IPEndPoint.

        /// </summary>

        /// <param name="ep">The IPEndPoint to connect to.</param>

        /// <returns>A DateTime containing the current time.</returns>

        public static DateTime GetNetworkTime(IPEndPoint ep)

        {

            Socket s = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

            s.Connect(ep);

            byte[] ntpData = new byte[48]; // RFC 2030 

            ntpData[0] = 0x1B;

            for (int i = 1; i < 48; i++)

                ntpData[i] = 0;

            s.Send(ntpData);

            s.Receive(ntpData);

            byte offsetTransmitTime = 40;

            ulong intpart = 0;

            ulong fractpart = 0;

            for (int i = 0; i <= 3; i++)

                intpart = 256 * intpart + ntpData[offsetTransmitTime + i];

            for (int i = 4; i <= 7; i++)

                fractpart = 256 * fractpart + ntpData[offsetTransmitTime + i];

            ulong milliseconds = (intpart * 1000 + (fractpart * 1000) / 0x100000000L);

            s.Close();

            TimeSpan timeSpan = TimeSpan.FromTicks((long)milliseconds * TimeSpan.TicksPerMillisecond);

            DateTime dateTime = new DateTime(1900, 1, 1);

            dateTime += timeSpan;

            TimeSpan offsetAmount = TimeZone.CurrentTimeZone.GetUtcOffset(dateTime);

            DateTime networkDateTime = (dateTime + offsetAmount);

            return networkDateTime;

        }

    }

}