Joao Girão João Paulo Barraca Bernd Lamparter Dirk Westhoff Rui L. Aguiar QoS-Differentiated Secure Charging in Ad-Hoc Environments. 1093-1100 http://springerlink.metapress.com/openurl.asp?genre=article&issn=0302-9743&volume=3124&spage=1093 2004 conf/ict/2004 ICT db/conf/ict/ict2004.html#GiraoBLWA04