How to place an imageview on top of another imageview in android

This is my layout which i tried so far without any success

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@color/white">

 <LinearLayout 
    android:id="@+id/lltest" 
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:layout_centerHorizontal="true">

        <ImageView 
        android:id="@+id/inside_imageview" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:layout_marginTop="5dip"
        android:layout_marginBottom="5dip"
        android:src="@drawable/frame"/>

</LinearLayout>

 <ImageView 
        android:id="@+id/outside_imageview" 
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        android:layout_alignTop="@id/inside_imageview"
        android:scaleType="fitXY"/>
</RelativeLayout>

What i exactly want is to have my outside_imageview on top of inside_imageview with the exact height and width... How to do it through layout?