如何使用DotRas连接USB 3G调制解调器并发送AT命令

我发现DotRas是RAS的包装器。这就是我能用它做的

private void btnConnect_Click(object sender, EventArgs e)
    {
        RasDevice device = RasDevice.GetDeviceByName("ZTE Proprietary USB Modem", RasDeviceType.Modem);
        if (device != null)
        {
            MessageBox.Show("Found "+device.Name.ToString()+device.DeviceType.ToString(), "hah!", MessageBoxButtons.OK);
        }
        else
        {
            MessageBox.Show("Device not found", "Error", MessageBoxButtons.OK);
        }
        this.rasPhoneBook1.Open();
        RasEntry entry = RasEntry.CreateDialUpEntry("ZTE Proprietary USB Modem", "+880000000", device);
        this.rasPhoneBook1.Entries.Add(entry);
        this.rasDialer1.EntryName = "ZTE Proprietary USB Modem";
        this.rasDialer1.PhoneBookPath = rasPhoneBook1.Path;
        this.rasDialer1.DialAsync();
    }
    private void rasDialer1_StateChanged(object sender, StateChangedEventArgs e)
    {
        MessageBox.Show(e.State.ToString(), "Dial Status", MessageBoxButtons.OK);
    }
    private void rasDialer1_DialCompleted(object sender, DialCompletedEventArgs e)
    {
        if (e.Cancelled)
        {
            MessageBox.Show("Cancelled");
        }
        else if (e.TimedOut)
        {
            MessageBox.Show("Time out");
        }
        else if (e.Error != null)
        {
            MessageBox.Show(e.Error.ToString(),"Error");
        }
        else if (e.Connected)
        {
            MessageBox.Show("Connection successful!");
        }
    }   

代码尝试拨号调制解调器，但显示以下错误消息：

"The remote computer did not respond. To make sure that the server can be reached,ping the remote    computer."}

错误显示在这里：

 else if (e.Error != null)
        {
            MessageBox.Show(e.Error.ToString(),"Error");
        } 

我正在尝试连接3g调制解调器，并通过调制解调器发送和接收短信。我怎样才能用DotRas做到这一点是的，我已经阅读了API文档，并阅读了DOtRas官方网站上的讨论，但我仍然迷失了方向。任何帮助都将不胜感激。非常感谢。