h:command link not executed

Question

I have a datatable in my jsf page and I need to have an index for this table. In this index I have links like as follows :

<h:commandLink value="2 " action="#{index.findByCat()}">
  <f:param name="tpage" value="10"></f:param>
  <f:param name="cat" value="#{index.cat}"></f:param>
  <f:ajax render=":tg"></f:ajax>
</h:commandLink>

But the method defined as action is not executed when I click the link.