2.2.22 P-Agent-On-Behalf-Of Header Field Syntax

This protocol defines a header field called P-Agent-On-Behalf-Of.<16> If a client endpoint attempts to establish a call on behalf of, it MUST use the P-Agent-On-Behalf-Of header field.

The ABNF, as defined in [RFC5234], for the P-Agent-On-Behalf-Of header field is specified as follows:

 "P-Agent-On-Behalf-Of" HCOLON name-addr / addr-spec

HCOLON, name-addr and addr-spec are specified in [RFC3261] section 25. This header SHOULD be present only in a SIP INVITE.

The server endpoint can use a back-to-back agent to establish the call. If the server endpoint cannot provide the service, it SHOULD decline the request.