关于一个 NetworkStream 异常的问题

networkstream  read 方法跟 DataAvailable  引发的一个 System.IO.IOException  异常要怎么去避免?
  哪位知道? private int ReadLine(string mail)
        {
            int reCode = 0;
            string retMsg = String.Empty;
            try
            {
                byte[] readbuffer = new byte[1024 * 2];
                ns.ReadTimeout = TimeOut;
                if (ns.CanRead)
                {
                    do
                    {
                        ns.Read(readbuffer, 0, readbuffer.Length);
                        if (!string.IsNullOrEmpty(retMsg.Trim()))
                        {
                            try
                            {
                                reCode = Convert.ToInt32(retMsg.Trim().Substring(0, 3));
                            }
                            catch
                            {
                                reCode = 355;
                            }
                        }
                    }
                    while (ns.DataAvailable);
                    retMsg = System.Text.Encoding.ASCII.GetString(readbuffer);
                    AsyncText(retMsg);
                }
            }
            catch (System.IO.IOException errs)
            {
                AsyncText(" IO操作异常,网络基础流关闭,但邮件可能已发送成功");
                reCode = 355;
            }
            catch (ArgumentOutOfRangeException ers)
            {
                AsyncText("超时异常");
                reCode = 355;
            }
            catch (Exception esc)
            {
                AsyncText("读取信息异常");
                 reCode = 355;
            }
            //操作遇到失败
            if (reCode > 400)
            {
                WriteErrmail(mail);
            }
            return reCode;
        }