Marcelo Bagnulo Bernardo Alarcos María Calderón Marifeli Sedano Providing Authentication & Authorization Mechanisms for Active Service Charging. 337-346 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=2511&spage=337 2002 conf/qofis/2002 QofIS db/conf/qofis/qofis2002.html#BagnuloACS02