tion 7.5) in which an INVITE carries both a SDP mes- sage body (application/sdp) and an encapsulated ISUP message (application/isup) An example multipart MIME is: INVITE sip:refertarget@carol.example.com SIP/2.0 Via: SIP/2.0/UDE P referree.example;branch=z9hG4bkffe209934aad To: sip:refertarget@carol.example.com From: sip:referree@referree.example>;tag=290903402 Call-ID: e9023940-a3465@referree.example CSeq: 889823409 INVITE Max-Forwards: 70 Contact: <sip:referree@bob.example.com> Referred-By: sip:referror@alice.example.com ;cid=3C20398823.2UWQFN309shb3@alice.example.com3 Content-Type: multipart/mixed; boundary=-*-boundary-* Content-Length: *-boundary-* Content-Type: application/sdp Content-Length: o=referree 2890844526 2890844526 IN IP4 referree.example s=Session SDP SIP: Understanding the Session Initiation Protocol C=IN IP4 referree.example t=0 0 m=audio 49172 RTP/AVP 0 a=rtpmap: PCMU/8000 --*-boundary-*- Content-Type multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary=dragons39 Content-ID: <20398823.2UWQFN309shb3@alice.example.com> Content-Length: (appropriate value) -another-boundary- Content-Type message/sipfrag Content-Disposition: auth-id; handling=optional From: sip:referror@alice.example.com Date: Thu, 21 Feb 2002 13:02:03 GMT Call-ID: 2203900ef0299349d9209f023a Refer-To: sip:refertarget@carol.example.com Referred-By: sip:referror@alice.example.com ;cid=3C20398823.2UWQFN309shb3@alice.example.com31 -another-boundary- Content-Type: application/pkcs7-signature; name=smime.p7s Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename=smime.p7s;han- dling=required (S/MIME data goes here) -unique44- -*-boundary-* References Rosenberg, J., et al., "SIP: Session Initiation Protocol," RFC 3261, 2002. Sparks, R., "The Session Initiation Protocol (SIP) Refer Method," RFC 3515, 2003. Sparks, R., "Internet Media Type message/sipfrag," RFC 3420, 2003. Sparks, R., and A. Johnston, "SIP Call Control - Transfer," IETF Internet-Draft, Work in Progress, March 2003. Roach, A., "