Windows Phone 8.1 automatically close socket after 10 seconds

Question

try
{
    connectButton.IsEnabled = false;

    await _socket.ConnectAsync(new HostName(ipConnect.Text), "13928");
}
catch(ArgumentException)
{
    MessageDialog dlg = new MessageDialog("Неверный IP адрес");
    await dlg.ShowAsync();
}
catch
{
    MessageDialog dlg = new MessageDialog("Не удалось подключиться");
    await dlg.ShowAsync();
}

sr = new StreamReader(_socket.InputStream.AsStreamForRead());
sw = new StreamWriter(_socket.OutputStream.AsStreamForWrite());
string opAnswer = sr.ReadLine();

As server used Windows 10 UI app on PC with StreamSocketListener. After 10 seconds waiting response from server, opAnswer - null and socket closed.