IETF RFC 5360 PDF

SIP supports communications for several services, including real-time audio, video, text, instant messaging, and presence. In its current form, it allows session invitations, instant messages, and other requests to be delivered from one party to another without requiring explicit consent of the recipient. Without such consent, it is possible for SIP to be used for malicious purposes, including amplification and DoS (Denial of Service) attacks. This document identifies a framework for consent-based communications in SIP.