Android : admob ads doesn't show up

I made a simple app and added inside it an ad but it doesn't show up in the device.

and there is no errors in my code:

xml page:

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:ads="http://schemas.android.com/apk/res-auto"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/RelativeLayout1"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 tools:context=".MainActivity" 
 >

        <com.google.android.gms.ads.AdView
    xmlns:app="http://schemas.android.com/apk/libs/com.google.ads"
    android:id="@+id/adView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="66dp"
    ads:adSize="BANNER"
    ads:adUnitId="ad_ip" >
    </com.google.android.gms.ads.AdView>
    </RelativeLayout>