Core FTP Connection Timmed out expired issue.

below is all my code which i use to connect to FTP using SSL.

{
            FtpWebResponse response = null;
            string str = info.DomainName.Trim().ToString() + ":" + info.Port;
            string username = info.Username;
            string password = info.Password;
            FtpWebRequest request = (FtpWebRequest)WebRequest.Create(new Uri("ftp://" + str + "/" + dirName));

            try
            {
                request.Method = WebRequestMethods.Ftp.ListDirectory;
                request.Credentials = new NetworkCredential(username, password);
                request.KeepAlive = info.KeepAlive;
                request.Timeout = info.TimeOut;//900000
                request.ReadWriteTimeout = info.TimeOut;
                request.UsePassive = (!info.UsePassive);
                request.Proxy = null;
                request.EnableSsl = true;

                RemoteCertificateValidationCallback orgCallback = ServicePointManager.ServerCertificateValidationCallback;
                try
                {
                    ServicePointManager.ServerCertificateValidationCallback = new RemoteCertificateValidationCallback(OnValidateCertificate);
                    ServicePointManager.Expect100Continue = true;

                    response = (FtpWebResponse)request.GetResponse();
                    if (response.StatusCode.ToString() == "OpeningData")
                    {
                        response.Close();
                        return true;
                    }
                }
                finally
                {
                    ServicePointManager.ServerCertificateValidationCallback = orgCallback;
                }
               
            }
            catch (WebException ex)
            {
                if (request != null)
                {
                    request.Abort();
                }
                throw ex;
            }
            catch (Exception exx)
            {
                response.Close();
                throw exx;
            }
            return true;
        
}