Bradley Clayton Barry Irwin Alfredo Terzoli Integrating Secure RTP into the Open Source VoIP PBX Asterisk. 1-12 2006 ISSA http://icsa.cs.up.ac.za/issa/2006/Proceedings/Full/66_Paper.pdf conf/issa/2006 db/conf/issa/issa2006.html#ClaytonIT06