http://www.rfc-editor.org/rfc/rfc4484.txt
RFC 4484: Trait-Based Authorization Requirements for the Session Initiation Protocol (SIP), J. Peterson, J. Polk, D. Sicker, H. Tschofenig2006-08-01T23:00:00-00:00This document lays out a set of requirements related to trait-based authorization for the Session Initiation Protocol (SIP). While some authentication mechanisms are described in the base SIP specification, trait-based authorization provides information used to make policy decisions based on the attributes of a participant in a session. This approach provides a richer framework for authorization, as well as allows greater privacy for users of an identity system. This memo provides information for the Internet community.