no update on SAP HR driver received from SAP system


I'm able to set values for telephone number and fax from IDM vault to SAP HR system on a user that is synchronized with SAP HR but not able to get same attributes update from SAP HR system.
I want to have a bi-directional synchronization on that 2 attributes, the filter and mapping are correctly set on SAP HR driver.
Is there something I have to configure on SAP system to make IDM to listen on this attribute updates ?

Thanks for your help ;-)