Android สอบถามปัญหาเกี่ยวกับการเชื่อมต่อ Webservice ไม่ได้

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.widget.Toast;

import org.ksoap2.SoapEnvelope;
import org.ksoap2.serialization.SoapObject;
import org.ksoap2.serialization.SoapSerializationEnvelope;
import org.ksoap2.transport.HttpTransportSE;
import org.xmlpull.v1.XmlPullParserException;


public class MainActivity extends ActionBarActivity {
    private static final String SOAP_ACTION = "http://tempuri.org/CelsiusToFahrenheit";
    private static final String METHOD_NAME = "CelsiusToFahrenheit";
    private static final String NAMESPACE = "http://tempuri.org/";
    private static final String URL = "http://www.w3schools.com/webservices/tempconvert.asmx";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tv = (TextView)findViewById(R.id.tv);

        SoapObject Request = new SoapObject(NAMESPACE,METHOD_NAME);
        Request.addProperty("Celsius",32);

        SoapSerializationEnvelope soapEnvelope = new SoapSerializationEnvelope(SoapEnvelope.VER11);
        soapEnvelope.dotNet = true;
        soapEnvelope.setOutputSoapObject(Request);

        HttpTransportSE androidHttpTransport = new HttpTransportSE(URL);
        try {
            androidHttpTransport.call(SOAP_ACTION, soapEnvelope);
            SoapObject resultString = (SoapObject) soapEnvelope.bodyIn;

            if(resultString !=null){
                tv.setText(resultString.getProperty(0).toString());
            }else {
                Toast.makeText(getApplicationContext(),"Web Service not Response!",Toast.LENGTH_SHORT).show();
            }

        }
        catch (Exception e)
        {
            e.printStackTrace();
            Toast.makeText(getApplicationContext(),"Web Service not Connect!",Toast.LENGTH_SHORT).show();
        }

    }