how i know when FTP is disconnected while downloading file in C#.net

try
{
Stream strLocal;
                WebProxy wp = new WebProxy();
                wp.UseDefaultCredentials = true;//Create FTP request 
                FtpWebRequest request = FtpWebRequest.Create(FTPAddress) as FtpWebRequest;
                request.Proxy = wp;
                request = FtpWebRequest.Create(FTPAddress) as FtpWebRequest;
                request.Method = WebRequestMethods.Ftp.DownloadFile;
                request.Proxy = wp;
                request.ServicePoint.ConnectionLimit = 10;
                request.UsePassive = true;
                request.UseBinary = true;
                request.KeepAlive = false; //close the connection when done
                request.ContentOffset = StartPoint;
                //Stream reader = request.GetRequestStreamAsync();
                Stream reader = request.GetResponse().GetResponseStream();
                byte[] buffer = new byte[1048576]; //downloads in chuncks
                if (!File.Exists(filename))
                {
                    strLocal = new FileStream(filename, FileMode.Create, FileAccess.Write, FileShare.ReadWrite);
                }
                else
                {
                    File.Delete(filename);
                    strLocal = new FileStream(filename, FileMode.Create, FileAccess.Write, FileShare.ReadWrite);

                }
                int bytesSize = 0;
                while ((bytesSize = reader.Read(buffer, 0, buffer.Length)) > 0)
                {
                     
                    if ((strLocal.Length + bytesSize) < length)
                    {
                        strLocal.Write(buffer, 0, bytesSize);
                        this.Invoke(new UpdateProgessCallback(this.UpdateProgress), new object[] { strLocal.Length, length, i, Partfilename, bytesSize });
                    }
                    else
                    {
                        long Valtowrite = (strLocal.Length + bytesSize) - length;
                        Valtowrite = bytesSize - Valtowrite;
                        strLocal.Write(buffer, 0, (int)Valtowrite);
                        this.Invoke(new UpdateProgessCallback(this.UpdateProgress), new object[] { strLocal.Length, length, i, Partfilename, bytesSize });
                        break;
                    }

                }

                strLocal.Close();
}
catch (System.Net.WebException ex)
          {
          }
          catch (Exception ex)
          {
              MessageBox.Show(ex.Message, "There was an error connecting to the FTP Server.");
          }