Complete Listing

using System;
using System.Collections.Generic;
using System.Text;using System.Net;
using System.Net.Sockets;

namespace WpfApplication1
{
  class SNTP
  {

      public string TimeServer { get; set; }
      private UdpClient UDP = new UdpClient();
      public class SNTPpacket
      {
          public byte LI { get; set; }
          public byte VN { get; set; }
          public byte Mode { get; set; }
          public byte Stratum { get; set; }
          public byte Poll { get; set; }
          public byte Precision { get; set; }
          public Int32 RootDelay { get; set; }
          public Int32 RootDispersion { get; set; }
          public string RefId { get; set; }
          public DateTime RefTimeStamp { get; set; }
          public DateTime OriginateTimeStamp { get; set; }
          public DateTime ReceiveTimeStamp { get; set; }
          public DateTime TransmitTimeStamp { get; set; }
          public byte[] buffer { get; set; }

          public SNTPpacket()
          {
              buffer = new byte[48];
          }
          public void ConvertToBuffer()
          {
              buffer[0] = (byte)(((LI & 0x3) << 6) | ((VN & 0x3) << 3) |
                                                                     Mode & 0x07);
              buffer[1] = Stratum;
              buffer[2] = Poll;
              buffer[3] = Precision;
              Int64 SNTPTime =
                                     ConvertToSNTPTime(RefTimeStamp);
              LoadSNTPTime(SNTPTime, 24);
          }
          public void ConvertFromBuffer()
          {
              Mode = (byte)(buffer[0] & 0x7);
              VN = (byte)((buffer[0] >> 3) & 0x7);
              LI = (byte)((buffer[0] >> 6) & 0x3);
              Stratum = buffer[1];
              Poll = buffer[2];
              Precision = buffer[3];
              RootDelay = convertInt32(4);
              RootDispersion = convertInt32(8);
              RefId = Encoding.ASCII.GetString(buffer, 12, 4);
              RefTimeStamp = ConvertFromSNTPTime(16);
              OriginateTimeStamp = ConvertFromSNTPTime(24);
              ReceiveTimeStamp = ConvertFromSNTPTime(32);
              TransmitTimeStamp = ConvertFromSNTPTime(40);
          }

          private Int64 ConvertToSNTPTime(DateTime T)
          {
              return T.Subtract(new DateTime(1900, 1, 1)).Ticks /
                                                       TimeSpan.TicksPerSecond;
          }
          private void LoadSNTPTime(Int64 T, int start)
          {
              byte[] temp = BitConverter.GetBytes(T);
              for (int i = 0; i < 4; i++)
              {
                  buffer[start + 3 - i] = temp[i];
              }

           }
          private Int32 convertInt32(int start)
          {
              byte[] temp = new byte[4];
              for (int i = 0; i < 4; i++)
              {
                  temp[i] = buffer[start + 3 - i];
              }
              return BitConverter.ToInt32(temp, 0);
          }
          private DateTime ConvertFromSNTPTime(int start)
          {
              byte[] tempHigh = new byte[4];
              byte[] tempLow = new byte[4];
              for (int i = 0; i < 4; i++)
              {
                  tempHigh[i] = buffer[start + 3 - i];
                  tempLow[i] = buffer[start + 4 + 3 - i];
              }

              UInt32 tempTime = BitConverter.ToUInt32(tempHigh, 0);
              UInt32 tempFrac = BitConverter.ToUInt32(tempLow, 0);
              double SNTPTime = tempTime + ((double)tempFrac) /
                                                   ((double)UInt32.MaxValue + 1);
              return new DateTime(1900, 1, 1).
                                                       AddSeconds(SNTPTime); ;
          }
      }

      public SNTPpacket SNTPRequest()
      {
          SNTPpacket request = new SNTPpacket();
          request.VN = 1;
          request.Mode = 3;
          request.RefTimeStamp = DateTime.UtcNow;
          request.ConvertToBuffer();
          UDP.Connect(TimeServer, 123);
          int count = UDP.Send(request.buffer,
                                                          request.buffer.Length);
          IPEndPoint remoteEP=new IPEndPoint(IPAddress.Any,0);
          SNTPpacket reply = new SNTPpacket();
          reply.buffer = UDP.Receive(ref remoteEP);
          reply.ConvertFromBuffer();
          return reply;
      }

   }
}

Code for this project is available from the CodeBin. 

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