diff --git a/app/src/main/java/org/traccar/client/TrackingController.java b/app/src/main/java/org/traccar/client/TrackingController.java
index bc70b96..a5f2dfe 100644
--- a/app/src/main/java/org/traccar/client/TrackingController.java
+++ b/app/src/main/java/org/traccar/client/TrackingController.java
@@ -17,11 +17,17 @@ package org.traccar.client;
 
 import android.content.Context;
 import android.content.SharedPreferences;
+import android.os.Handler;
 import android.preference.PreferenceManager;
 
 public class TrackingController implements PositionProvider.PositionListener {
 
+    private static final int RETRY_DELAY = 30 * 1000;
+
+    private boolean isWaiting;
+
     private Context context;
+    private Handler handler;
     private SharedPreferences preferences;
 
     private PositionProvider positionProvider;
@@ -29,6 +35,7 @@ public class TrackingController implements PositionProvider.PositionListener {
 
     public TrackingController(Context context) {
         this.context = context;
+        handler = new Handler();
         preferences = PreferenceManager.getDefaultSharedPreferences(context);
         positionProvider = new PositionProvider(context, this,
                 preferences.getString(MainActivity.KEY_DEVICE, null),
@@ -43,31 +50,98 @@ public class TrackingController implements PositionProvider.PositionListener {
 
     public void stop() {
         positionProvider.stopUpdates();
+        handler.removeCallbacksAndMessages(null);
     }
 
     @Override
     public void onPositionUpdate(Position position) {
         if (position != null) {
             StatusActivity.addMessage(context.getString(R.string.status_location_update));
-
-
-
-            String request = ProtocolFormatter.formatRequest(
-                    preferences.getString(MainActivity.KEY_ADDRESS, null),
-                    Integer.parseInt(preferences.getString(MainActivity.KEY_PORT, null)),
-                    position);
-
-            RequestManager.sendRequestAsync(request, new RequestManager.RequestHandler() {
-                @Override
-                public void onSuccess() {
-                }
-
-                @Override
-                public void onFailure() {
-                    StatusActivity.addMessage(context.getString(R.string.status_send_fail));
-                }
-            });
+            write(position);
         }
     }
 
+    //
+    // write -> read -> send -> delete -> read
+    //
+    // read -> send -> retry -> read -> send
+    //
+
+    private void read() {
+        databaseHelper.selectPositionAsync(new DatabaseHelper.DatabaseHandler<Position>() {
+            @Override
+            public void onSuccess(Position result) {
+                if (result != null) {
+                    send(result);
+                } else {
+                    isWaiting = true;
+                }
+            }
+
+            @Override
+            public void onFailure(RuntimeException error) {
+                retry();
+            }
+        });
+    }
+
+    private void write(Position position) {
+        databaseHelper.insertPositionAsync(position, new DatabaseHelper.DatabaseHandler<Void>() {
+            @Override
+            public void onSuccess(Void result) {
+                if (isWaiting) {
+                    read();
+                    isWaiting = false;
+                }
+            }
+
+            @Override
+            public void onFailure(RuntimeException error) {
+            }
+        });
+    }
+
+    private void delete(Position position) {
+        databaseHelper.deletePositionAsync(position.getId(), new DatabaseHelper.DatabaseHandler<Void>() {
+            @Override
+            public void onSuccess(Void result) {
+                read();
+            }
+
+            @Override
+            public void onFailure(RuntimeException error) {
+                retry();
+            }
+        });
+    }
+
+    private void send(final Position position) {
+        String request = ProtocolFormatter.formatRequest(
+                preferences.getString(MainActivity.KEY_ADDRESS, null),
+                Integer.parseInt(preferences.getString(MainActivity.KEY_PORT, null)),
+                position);
+
+        RequestManager.sendRequestAsync(request, new RequestManager.RequestHandler() {
+            @Override
+            public void onSuccess() {
+                delete(position);
+            }
+
+            @Override
+            public void onFailure() {
+                StatusActivity.addMessage(context.getString(R.string.status_send_fail));
+                retry();
+            }
+        });
+    }
+
+    private void retry() {
+        handler.postDelayed(new Runnable() {
+            @Override
+            public void run() {
+                read();
+            }
+        }, RETRY_DELAY);
+    }
+
 }