I need to place a linear layout at bottom inside a relativelayout which is the top most parent in xml. How can i do this?

Please help me.

 <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="@drawable/background"
android:orientation="vertical" >
<RelativeLayout .......   <<--- this should occupy total available space
</Relativelayout
 <Linearlayout .......     <<-- this should place at bottom always with height 50dp
 </LineaLayout>
 </ReltiveLayout>