请求内容过长，HttpWebRequest导致异常：基础连接关闭

请求内容过长，HttpWebRequest导致异常：基础连接关闭，这个应该如何解决？？？

private string HttpPost(string url, string param)
        {
            HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
            Encoding encoding = Encoding.UTF8;

            byte[] bs = Encoding.UTF8.GetBytes(param);
            string responseData = string.Empty;

            request.Method = "POST";
            request.ContentType = "application/json; charset=UTF-8";
            request.ContentLength = bs.Length;

            using (Stream reqStream = request.GetRequestStream())
            {
                reqStream.Write(bs, 0, bs.Length);
            }
            using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
            {
                using (StreamReader reader = new StreamReader(response.GetResponseStream(), encoding))
                {
                    responseData = reader.ReadToEnd().ToString();
                }
            }


            return responseData;
        }

原因是因为服务器不允许与 Internet 资源建立持久性连接连接和http的版本造成的