This set of slide is from “The Art of VoIP Hacking”, a workshop that was held at Defcon 23.
You can download it from the following link: https://packetstormsecurity.com/files/download/133117/The_Art_of_VoIP_Workshop_v1.0_8Aug15.pdf
Source: https://packetstormsecurity.com/files/133117/The-Art-Of-VoIP-Hacking.html