This document describes a private Session Initiation Protocol (SIP)

header field (P-header) to be used by the European Telecommunications

Standards Institute (ETSI) Telecommunications and Internet-converged

Services and Protocols for Advanced Networks (TISPAN) for the purpose

of authorizing early media flows in Third Generation Partnership

Project (3GPP) IP Multimedia Subsystems (IMS). This header field is

useful in any SIP network that is interconnected with other SIP

networks and needs to control the flow of media in the early dialog

state.