I have developed client server Application .I am accessing mysql with php running on my machine and client running on my cell which is connected to machine.WI-FI is also switched ON.

Internet Permission are also added in Manifest file but then also the i encounter error

172.20.38.143 is IP OF MY MACHINE

  06-01 13:20:10.391: W/System.err(11157): org.apache.http.conn.HttpHostConnectException: Connection to http://172.20.38.143 refused
06-01 13:20:10.401: W/System.err(11157):    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:183)
06-01 13:20:10.401: W/System.err(11157):    at org.apache.http.impl.conn.AbstractPoolEntry.open(AbstractPoolEntry.java:164)
06-01 13:20:10.401: W/System.err(11157):    at org.apache.http.impl.conn.AbstractPooledConnAdapter.open(AbstractPooledConnAdapter.java:119)
06-01 13:20:10.401: W/System.err(11157):    at org.apache.http.impl.client.DefaultRequestDirector.execute(DefaultRequestDirector.java:360)
06-01 13:20:10.401: W/System.err(11157):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:674)
06-01 13:20:10.401: W/System.err(11157):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:511)
06-01 13:20:10.401: W/System.err(11157):    at org.apache.http.impl.client.AbstractHttpClient.execute(AbstractHttpClient.java:489)
06-01 13:20:10.401: W/System.err(11157):    at nineandroid.net.example.library.JSONParser.getJSONFromUrl(JSONParser.java:42)
06-01 13:20:10.401: W/System.err(11157):    at nineandroid.net.example.library.UserFunctions.registerUser(UserFunctions.java:59)
06-01 13:20:10.401: W/System.err(11157):    at nineandroid.net.example.RegisterActivity$1.onClick(RegisterActivity.java:52)
06-01 13:20:10.411: W/System.err(11157):    at android.view.View.performClick(View.java:3567)
06-01 13:20:10.411: W/System.err(11157):    at android.view.View$PerformClick.run(View.java:14224)
06-01 13:20:10.411: W/System.err(11157):    at android.os.Handler.handleCallback(Handler.java:605)
06-01 13:20:10.411: W/System.err(11157):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-01 13:20:10.411: W/System.err(11157):    at android.os.Looper.loop(Looper.java:137)
06-01 13:20:10.411: W/System.err(11157):    at android.app.ActivityThread.main(ActivityThread.java:4517)
06-01 13:20:10.411: W/System.err(11157):    at java.lang.reflect.Method.invokeNative(Native Method)
06-01 13:20:10.411: W/System.err(11157):    at java.lang.reflect.Method.invoke(Method.java:511)
06-01 13:20:10.411: W/System.err(11157):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
06-01 13:20:10.421: W/System.err(11157):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
06-01 13:20:10.421: W/System.err(11157):    at dalvik.system.NativeStart.main(Native Method)
06-01 13:20:10.421: W/System.err(11157): Caused by: java.net.ConnectException: failed to connect to /172.20.38.143 (port 80): connect failed: ENETUNREACH (Network is unreachable)
06-01 13:20:10.431: W/System.err(11157):    at libcore.io.IoBridge.connect(IoBridge.java:114)
06-01 13:20:10.431: W/System.err(11157):    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:192)
06-01 13:20:10.431: W/System.err(11157):    at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:459)
06-01 13:20:10.431: W/System.err(11157):    at java.net.Socket.connect(Socket.java:848)
06-01 13:20:10.431: W/System.err(11157):    at org.apache.http.conn.scheme.PlainSocketFactory.connectSocket(PlainSocketFactory.java:119)
06-01 13:20:10.431: W/System.err(11157):    at org.apache.http.impl.conn.DefaultClientConnectionOperator.openConnection(DefaultClientConnectionOperator.java:144)
06-01 13:20:10.431: W/System.err(11157):    ... 20 more
06-01 13:20:10.431: W/System.err(11157): Caused by: libcore.io.ErrnoException: connect failed: ENETUNREACH (Network is unreachable)
06-01 13:20:10.441: W/System.err(11157):    at libcore.io.Posix.connect(Native Method)
06-01 13:20:10.441: W/System.err(11157):    at libcore.io.BlockGuardOs.connect(BlockGuardOs.java:85)
06-01 13:20:10.441: W/System.err(11157):    at libcore.io.IoBridge.connectErrno(IoBridge.java:127)
06-01 13:20:10.441: W/System.err(11157):    at libcore.io.IoBridge.connect(IoBridge.java:112)
06-01 13:20:10.441: W/System.err(11157):    ... 25 more
06-01 13:20:10.441: E/Buffer Error(11157): Error converting result java.lang.NullPointerException
06-01 13:20:10.451: E/JSON Parser(11157): Error parsing data org.json.JSONException: End of input at character 0 of 
06-01 13:20:10.451: D/AndroidRuntime(11157): Shutting down VM
06-01 13:20:10.451: W/dalvikvm(11157): threadid=1: thread exiting with uncaught exception (group=0x40c0aa68)
06-01 13:20:10.451: E/AndroidRuntime(11157): FATAL EXCEPTION: main
06-01 13:20:10.451: E/AndroidRuntime(11157): java.lang.NullPointerException
06-01 13:20:10.451: E/AndroidRuntime(11157):    at nineandroid.net.example.RegisterActivity$1.onClick(RegisterActivity.java:56)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at android.view.View.performClick(View.java:3567)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at android.view.View$PerformClick.run(View.java:14224)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at android.os.Handler.handleCallback(Handler.java:605)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at android.os.Handler.dispatchMessage(Handler.java:92)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at android.os.Looper.loop(Looper.java:137)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at android.app.ActivityThread.main(ActivityThread.java:4517)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at java.lang.reflect.Method.invokeNative(Native Method)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at java.lang.reflect.Method.invoke(Method.java:511)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)
06-01 13:20:10.451: E/AndroidRuntime(11157):    at dalvik.system.NativeStart.main(Native Method)

UserFunctions.java to call jsonParser

public class UserFunctions {

private JSONParser jsonParser;

private static String loginURL = "http://172.20.38.143/ah_login_api/";
private static String registerURL = "http://172.20.38.143/ah_login_api/";

private static String login_tag = "login";
private static String register_tag = "register";

// constructor
public UserFunctions(){
    jsonParser = new JSONParser();
}

/**
 * function make Login Request
 * @param email
 * @param password
 * */
public JSONObject loginUser(String email, String password){
    // Building Parameters
    List<NameValuePair> params = new ArrayList<NameValuePair>();
    params.add(new BasicNameValuePair("tag", login_tag));
    params.add(new BasicNameValuePair("email", email));
    params.add(new BasicNameValuePair("password", password));
    JSONObject json = jsonParser.getJSONFromUrl(loginURL, params);
    // return json
    // Log.e("JSON", json.toString());
    return json;
}

/**
 * function make Login Request
 * @param name
 * @param email
 * @param password
 * */
public JSONObject registerUser(String name, String email, String password){
    // Building Parameters
    List<NameValuePair> params = new ArrayList<NameValuePair>();
    params.add(new BasicNameValuePair("tag", register_tag));
    params.add(new BasicNameValuePair("name", name));
    params.add(new BasicNameValuePair("email", email));
    params.add(new BasicNameValuePair("password", password));

    // getting JSON Object
    JSONObject json = jsonParser.getJSONFromUrl(registerURL, params);
    // return json
    return json;
}

/**
 * Function get Login status
 * */
public boolean isUserLoggedIn(Context context){
    DatabaseHandler db = new DatabaseHandler(context);
    int count = db.getRowCount();
    if(count > 0){
        // user logged in
        return true;
    }
    return false;
}

/**
 * Function to logout user
 * Reset Database
 * */
public boolean logoutUser(Context context){
    DatabaseHandler db = new DatabaseHandler(context);
    db.resetTables();
    return true;
}
}

jsonParser.java

public class JSONParser {

static InputStream is = null;
static JSONObject jObj = null;
static String json = "";

// constructor
public JSONParser() {

}

public JSONObject getJSONFromUrl(String url, List<NameValuePair> params) {

    // Making HTTP request
    try {
        // defaultHttpClient
        DefaultHttpClient httpClient = new DefaultHttpClient();
        HttpPost httpPost = new HttpPost(url);
        httpPost.setEntity(new UrlEncodedFormEntity(params));

        HttpResponse httpResponse = httpClient.execute(httpPost);
        HttpEntity httpEntity = httpResponse.getEntity();
        is = httpEntity.getContent();

    } catch (UnsupportedEncodingException e) {
        e.printStackTrace();
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }

    try {
        BufferedReader reader = new BufferedReader(new InputStreamReader(
                is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        while ((line = reader.readLine()) != null) {
            sb.append(line + "\n");
        }
        is.close();
        json = sb.toString();
        Log.e("JSON", json);
    } catch (Exception e) {
        Log.e("Buffer Error", "Error converting result " + e.toString());
    }

    // try parse the string to a JSON object
    try {
        jObj = new JSONObject(json);            
    } catch (JSONException e) {
        Log.e("JSON Parser", "Error parsing data " + e.toString());
    }

    // return JSON String
    return jObj;

}

}

RegisterActivity.java

public class RegisterActivity extends Activity {
    Button btnRegister;
Button btnLinkToLogin;
EditText inputFullName;
EditText inputEmail;
EditText inputPassword;
TextView registerErrorMsg;

// JSON Response node names
private static String KEY_SUCCESS = "success";
private static String KEY_UID = "uid";
private static String KEY_NAME = "name";
private static String KEY_EMAIL = "email";
private static String KEY_CREATED_AT = "created_at";

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.register);

    // Importing all assets like buttons, text fields
    inputFullName = (EditText) findViewById(R.id.registerName);
    inputEmail = (EditText) findViewById(R.id.registerEmail);
    inputPassword = (EditText) findViewById(R.id.registerPassword);
    btnRegister = (Button) findViewById(R.id.btnRegister);
    btnLinkToLogin = (Button) findViewById(R.id.btnLinkToLoginScreen);
    registerErrorMsg = (TextView) findViewById(R.id.register_error);

    // Register Button Click event
    btnRegister.setOnClickListener(new View.OnClickListener() {         
        public void onClick(View view) {
            String name = inputFullName.getText().toString();
            String email = inputEmail.getText().toString();
            String password = inputPassword.getText().toString();
            UserFunctions userFunction = new UserFunctions();
            JSONObject json = userFunction.registerUser(name, email, password);

            // check for login response
            try {
                if (json.getString(KEY_SUCCESS) != null) {
                    registerErrorMsg.setText("");
                    String res = json.getString(KEY_SUCCESS); 
                    if(Integer.parseInt(res) == 1){
                        // user successfully registred
                        // Store user details in SQLite Database
                        DatabaseHandler db = new DatabaseHandler(getApplicationContext());
                        JSONObject json_user = json.getJSONObject("user");

                        // Clear all previous data in database
                        userFunction.logoutUser(getApplicationContext());
                        db.addUser(json_user.getString(KEY_NAME), json_user.getString(KEY_EMAIL), json.getString(KEY_UID), json_user.getString(KEY_CREATED_AT));                        
                        // Launch Dashboard Screen
                        Intent dashboard = new Intent(getApplicationContext(), DashboardActivity.class);
                        // Close all views before launching Dashboard
                        dashboard.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                        startActivity(dashboard);
                        // Close Registration Screen
                        finish();
                    }else{
                        // Error in registration
                        registerErrorMsg.setText("Error occured in registration");
                    }
                }
            } catch (JSONException e) {
                e.printStackTrace();
            }
        }
    });

    // Link to Login Screen
    btnLinkToLogin.setOnClickListener(new View.OnClickListener() {

        public void onClick(View view) {
            Intent i = new Intent(getApplicationContext(),
                    LoginActivity.class);
            startActivity(i);
            // Close Registration View
            finish();
        }
    });
}

}