xsl-fo:header, body, and footer overlapped

I am trying to convert an xml file into a PDF file. 
I have some tried various ways to prevent the body
content expanded down to the footer region.  In some
pages, the body content will overlap with the footer. 

I wonder how I should set the layout-master-set.
My code is as follows:

<fo:layout-master-set>
     <fo:simple-page-master master-name="report"
	 page-height="29.7cm"
	 page-width="21cm"
	 margin-top="1cm"
	 margin-bottom="3cm"
	 margin-left="2cm"
	 margin-right="2cm">
	 <fo:region-body margin-top="1cm"/>
	 <fo:region-before extent="1cm"/>
	 <fo:region-after extent="1cm"/>
     </fo:simple-page-master>
</fo:layout-master-set>

Thanks.

Yan


__________________________________________________
Do You Yahoo!?
Send your FREE holiday greetings online!
http://greetings.yahoo.com

 XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list