C#

I am using following code to download file from FTP. I want to enhance this code with Auto Resume functionality in case of Internet disconnection. This code works perfect to download a file but doesn't auto resume. Please provide me C# source code to apply auto resume. My code supports bigger file also that is multiple GB download. Please review my code and please suggest how in my code I can integrate Resume.

\\\\\\\\\\\\\\\\\\\\ code 
try
    {

        //Create FTP Request.
        FtpWebRequest request = (FtpWebRequest)WebRequest.Create(FTPPath);
        request.Method = WebRequestMethods.Ftp.DownloadFile;

        //Enter FTP Server credentials.
        request.Credentials = new NetworkCredential(FTPUser, FTPPassword);
        request.UsePassive = true;
        request.UseBinary = true;
        request.EnableSsl = false;

        FtpWebResponse response = (FtpWebResponse)request.GetResponse();
        using (Stream stream = response.GetResponseStream())
        {
            int length = 0;
            int bytesToRead = 26214400;
            byte[] buffer = new Byte[bytesToRead]; // Buffer to read bytes in chunk size specified above

            long responseFileLength = this.FtpGetFileSize(FTPPath, FTPUser, FTPPassword); // Get the file size on the ftp   

            HttpContext.Current.Response.Buffer = false;
            HttpContext.Current.Response.Clear();
            HttpContext.Current.Response.ClearContent();
            HttpContext.Current.Response.ClearHeaders();
            HttpContext.Current.Response.Expires = -1;

            
            HttpContext.Current.Response.ContentType = "application/octet-stream";
            HttpContext.Current.Response.AddHeader("Content-Disposition", "attachment; filename=\"" + origionalFileName + "\"");
            HttpContext.Current.Response.AddHeader("Content-Length", responseFileLength.ToString());

            
                do
                {
                    
                    if (HttpContext.Current.Response.IsClientConnected)
                    {
                        length = stream.Read(buffer, 0, bytesToRead);
                        HttpContext.Current.Response.OutputStream.Write(buffer, 0, length);
                        HttpContext.Current.Response.Flush();
                        buffer = new Byte[bytesToRead];
                    }
                    else
                    {
                        length = -1;
                    }
                } while (length > 0); //Repeat until no data is read
            
            IsDownloaded = true;
            HttpContext.Current.Response.Clear();
        }
            }
        catch (WebException ex)
        {
    
        }

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            button1.Text = "processing";
            int sum = 0;
            for (int i = 0; i <= 100; i++)
            {
                Thread.Sleep(100);
                sum = sum + i;
                backgroundWorker1.ReportProgress(i);
                if (backgroundWorker1.CancellationPending)
                {
                    e.Cancel = true;
                    backgroundWorker1.ReportProgress(0);
                    return;
                }
            }
            e.Result = sum;
        }


        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            progressBar1.Value = e.ProgressPercentage;
            label1.Text = e.ProgressPercentage + "%";

        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Cancelled)
            {
                label1.Text = "Process canceled";
            }
            else if (e.Error != null)
            {
                label1.Text = e.Error.Message;
            }
            else
            {
                label1.Text = "Result: " + e.Result.ToString();
            }

        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (!backgroundWorker1.IsBusy)
            {
                backgroundWorker1.RunWorkerAsync();
            }
            else
            {
                MessageBox.Show("Busy processing!. Please wait...");
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            if (backgroundWorker1.IsBusy)
            {
                backgroundWorker1.CancelAsync();
            }
            else
            {
                label1.Text = "No operation is running to cancel.";
            }
        }
    }