https://app.knowbase.one/vault/rfc/docid/4754
RFC4354: A Session Initiation Protocol (SIP) Event Package and Data Format for Various Settings in Support for the Push-to-Talk over Cellular (PoC) Service
Network Working Group M. Garcia-Martin Request for Comments: 4354 Nokia Category: Informational January 2006 A Session Initiation Protocol (SIP) Event Package and Data Format ...
https://app.knowbase.one/vault/rfc/docid/5792
RFC5318: The Session Initiation Protocol (SIP) P-Refused-URI-List Private-Header (P-Header)
Network Working Group J. Hautakorpi Request for Comments: 5318 G. Camarillo Category: Informational Ericsson December 2008 ...