https://app.knowbase.one/vault/rfc/docid/8804
RFC8101: IANA Registration of New Session Initiation Protocol (SIP) Resource-Priority Namespace for Mission Critical Push To Talk Service
Internet Engineering Task Force (IETF) C. Holmberg Request for Comments: 8101 J. Axell Category: Informational Ericsson ISSN: 2070-1721 March 2017 ...