Dimitris Geneiatakis Georgios Kambourakis Costas Lambrinoudakis A Mechanism for Ensuring the Validity and Accuracy of the Billing Services in IP Telephony. 59-68 2008 TrustBus http://dx.doi.org/10.1007/978-3-540-85735-8_7 conf/trustbus/2008 db/conf/trustbus/trustbus2008.html#GeneiatakisKL08