http://www.rfc-editor.org/rfc/rfc6141.txt
RFC 6141: Re-INVITE and Target-Refresh Request Handling in the Session Initiation Protocol (SIP), G. Camarillo, C. Holmberg, Y. Gao2011-03-01T23:00:00-00:00The procedures for handling SIP re-INVITEs are described in RFC 3261. Implementation and deployment experience has uncovered a number of issues with the original documentation, and this document provides additional procedures that update the original specification to address those issues. In particular, this document defines in which situations a UAS (User Agent Server) should generate a success response and in which situations a UAS should generate an error response to a re-INVITE. Additionally, this document defines further details of procedures related to target-refresh requests. [STANDARDS-TRACK]