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Versions: 00 01 02 03 04 RFC 5009

Network Working Group                                    Richard Ejzak
INTERNET-DRAFT                                          Alcatel-Lucent
                                                       January 1, 2007


      Private Header (P-Header) Extension to the Session Initiation
             Protocol (SIP) for Authorization of Early Media
                  <draft-ejzak-sipping-p-em-auth-03.txt>


Status of this memo

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   applicable patent or other IPR claims of which he or she is aware
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   This document is a submission of the IETF SIPPING WG.  Comments
   should be directed to the SIPPING WG mailing list, sipping@ietf.org.

Abstract

   This document describes a private Session Initiation Protocol (SIP)
   header (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 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.




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Table of Contents

1. Introduction....................................................2
2. Applicability Statement.........................................3
3. Conventions and Acronyms........................................3
4. Background on early media authorization.........................4
  4.1. Backward early media.......................................4
  4.2. Forward early media........................................5
5. Applicability of RFC 3959 and RFC 3960..........................6
6. Overview of Operation...........................................6
7. Limitations of the P-Early-Media header.........................8
8. The P-Early-Media header........................................8
  8.1. Procedures at the User Agent Client.......................10
  8.2. Procedures at the User Agent Server.......................10
  8.3. Procedures at the proxy...................................11
9. Formal syntax..................................................11
10. Security Considerations.......................................11
11. IANA Considerations...........................................12
  11.1. Registration of the "P-Early-Media" SIP header...........12
12. Acknowledgements..............................................12
13. References....................................................12
  13.1. Normative References.....................................12
  13.2. Informative References...................................13
14. Authors' Addresses............................................13
15. IPR Notice....................................................13
16. Copyright Notice..............................................14


1. Introduction

   This document defines the use of the P-Early-Media header for use
   within SIP [1] messages in certain SIP networks to authorize the
   cut-through of backward and/or forward early media. The P-Early-
   Media header is intended for use in a SIP network, such as a 3GPP
   IMS [13][14], that prohibits the exchange of early media between end
   users, that is interconnected with other SIP networks that have
   unknown, untrusted or different policies regarding early media, and
   that has the capability to "gate" (enable/disable) the flow of early
   media to/from user equipment.

   Within an isolated SIP network it is possible to gate early media
   associated with all endpoints within the network to enforce a
   desired early media policy among network endpoints.  However, when a
   SIP network is interconnected with other SIP networks, only the
   boundary node connected to the external network can determine which
   early media policy to apply to a session established between



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   endpoints on different sides of the boundary.  The P-Early-Media
   header provides a means for this boundary node to communicate this
   early media policy decision to other nodes within the network.


2. Applicability Statement

   The use of this extension is only applicable inside a 'Trust Domain'
   as defined in RFC 3325 [6].  Nodes in such a Trust Domain are
   explicitly trusted by its users and end-systems to authorize early
   media requests only when allowed by early media policy within the
   Trust Domain.

   This document does NOT offer a general early media authorization
   model suitable for inter-domain use or use in the Internet at large.
   Furthermore, since the early media requests are not
   cryptographically certified, they are subject to forgery, replay,
   and falsification in any architecture that does not meet the
   requirements of the Trust Domain.

   An early media request also lacks an indication of whom specifically
   is making or modifying the request, and so it must be assumed that
   the Trust Domain is making the request.  Therefore, the information
   is only meaningful when securely received from a node known to be a
   member of the Trust Domain.

   Although this extension can be used with parallel forking, it does
   not improve on the known problems with early media and parallel
   forking.

   Despite these limitations, there are sufficiently useful specialized
   deployments that meet the assumptions described above, and can
   accept the limitations that result, to warrant publication of this
   mechanism.  An example deployment would be a closed network that
   emulates a traditional circuit switched telephone network.


3. Conventions and Acronyms

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC2119 [2].

   The following acronyms are used in this document:

      3GPP   - the Third Generation Partnership Project
      ABNF   - Augmented Backus-Naur Form
      DTMF   - Dual Tone Multi-Frequency
      ETSI   - European Telecommunications Standards Institute



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      IMS    - Internet Protocol Multimedia Subsystem
      MIME   - Multipurpose Internet Mail Extensions
      NAT    - Network Address Translation
      PSTN   - Public Switched Telephone Network
      SDP    - Session Description Protocol
      SIP    - Session Initiation Protocol
      TISPAN - Telecommunications and Internet converged Services and
               Protocols for Advanced Networks
      UA     - User Agent
      UAC    - User Agent Client
      UAS    - User Agent Server


4. Background on early media authorization

   PSTN networks typically provide call progress information as
   backward early media from the terminating switch towards the calling
   party.  In a SIP network, backward early media flows from the User
   Agent Server (UAS) towards the User Agent Client (UAC).  PSTN
   networks also use forward early media from the calling party towards
   the terminating switch under some circumstances for applications
   such as digit collection for secondary dialing. In a SIP network,
   forward early media flows from the UAC towards the UAS.

   PSTN networks typically allow backward and/or forward early media
   since they are used for the purpose of progressing the call to the
   answer state and do not involve the exchange of data between
   endpoints. On the other hand, a SIP network may have a policy to
   prohibit backward early media from SIP user equipment and to
   prohibit forward media towards SIP user equipment, either of which
   may contain user data. A SIP network containing both PSTN gateways
   and SIP end devices, for example, can maintain such an early media
   policy by gating off any early media with a SIP end device acting as
   UAS, gating on early media with a SIP end device acting as UAC, and
   appropriately gating early media at each PSTN gateway.
   Unfortunately, a SIP network interconnected with another SIP network
   may have no means of assuring that the interconnected network is
   implementing a compatible early media policy.

   Without this extension, a SIP network interconnected with other SIP
   networks provides no mechanism for an originating SIP endpoint
   within the network, be it a PSTN gateway or SIP user equipment, from
   identifying if the terminating SIP endpoint, which may be located
   outside the network, is a SIP endpoint that is authorized either to
   send backward early media or to receive forward early media.


4.1. Backward early media




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   Backward early media in the PSTN typically comprises call progress
   information such as ringing, or announcements regarding special
   handling such as forwarding.  It may also include requests for
   further information, such as a credit card number to be entered as
   forward early media in the form of Dual Tone Multi-Frequency (DTMF)
   tones or speech. Backward early media of this type provides
   information to the calling party strictly for the purpose of
   progressing the call and involves no exchange of data between end
   users.  The usual PSTN charging policy assumes that no data is
   exchanged between users until the call has been answered.

   A terminating SIP User Agent (UA) outside of the SIP network, on the
   other hand, may provide any user data in a backward early media
   stream.  Thus if the network implements the usual early media
   policy, the network equipment gating the backward early media flow
   for the originating UA must distinguish between authorized early
   media from a terminating SIP endpoint and unauthorized early media
   from another SIP device outside of the network.  Given the
   assumption of a transitive trust relationship between SIP servers in
   the network, this can be accomplished by including some information
   in a backward SIP message that identifies the presence of authorized
   backward early media.  Since it is necessary to verify that this
   indication comes from a trusted source, it is necessary for each
   server on the path back to the originating UA be able to verify the
   trust relationship with the previous server and to remove such an
   indication when it cannot do so.  A server on the boundary to an
   untrusted SIP network can assure that no indication of authorized
   backward early media passes from an external UAS to a UAC within the
   network.  Thus the use of a private header that can be modified by
   SIP proxies is to be preferred over the use of a Multipurpose
   Internet Mail Extensions (MIME) attachment that cannot be modified
   in this way.


4.2. Forward early media

   Forward early media is less common than backward early media in the
   PSTN.  It is typically used to collect secondary dialed digits, to
   collect credit card numbers, or to collect other DTMF or speech
   responses for the purpose of further directing the call.  Forward
   early media in the PSTN is always directed toward a network server
   for the purpose of progressing a call and involves no exchange of
   data between end users.

   A terminating SIP UA outside of the SIP network, on the other hand,
   may receive any user data in a forward early media stream, thus if
   the network implements the usual early media policy, the network
   equipment gating the forward early media flow for the originating UA
   must distinguish between a terminating endpoint that is authorized



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   to receive forward early media, and another SIP device outside of
   the network that is not authorized to receive forward early media
   containing user data.  This authorization can be accomplished in the
   same manner as for backward early media by including some
   information in a backward SIP message that identifies that the
   terminating side is authorized to receive forward early media.


5. Applicability of RFC 3959 and RFC 3960

   The private header extension defined in this document is applicable
   to the gateway model defined in RFC 3960 [4], since the PSTN gateway
   is the primary requestor of early media in an IMS.  For the same
   reason, neither the application server model of RFC 3960, nor the
   early-session disposition type defined in RFC 3959 [3] is
   applicable.

   The gateway model of RFC 3960 [4] allows for individual networks to
   create local policy with respect to the handling of early media, but
   does not address the case where a network is interconnected with
   other networks with unknown, untrusted or different early media
   policies.  Without the kind of information in the P-Early-Media
   header, it is not possible for the network to determine whether cut-
   through of early media could lead to the transfer of data between
   end-users during session establishment.

   Thus the private header extension in this document is a natural
   extension of the gateway model of RFC 3960 [4] that is applicable
   within a transitive trust domain.


6. Overview of Operation

   This document defines a new P-Early-Media header field for the
   purpose of requesting and authorizing requests for backward and/or
   forward early media.  A UAC capable of recognizing the P-Early-Media
   header may include the header in an INVITE request.  The P-Early-
   Media header in an INVITE request contains no parameters.

   As members of the Trust Domain, each proxy receiving an INVITE
   request must decide whether to insert or delete the P-Early-Media
   header before forwarding.

   A UAS receiving an INVITE request can use the presence of the P-
   Early-Media header in the request to decide whether to request early
   media authorization in subsequent messages towards the UAC.  After
   receiving an incoming INVITE request, the UAS requesting backward
   and/or forward early media will include the P-Early-Media header in
   a message towards the UAC within the dialog, including direction



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   parameter(s) that identify for each media line in the session
   whether the early media request is for backward media, forward
   media, both or neither.  The UAS can change its request for early
   media by including a modified P-Early-Media header in a subsequent
   message towards the UAC within the dialog.

   Each proxy in the network receiving the P-Early-Media header in a
   message towards the UAC has the responsibility for assuring that the
   early media request comes from an authorized source.  If a P-Early-
   Media header arrives from either an untrusted source, a source not
   allowed to send backward early media, or a source not allowed to
   receive forward early media, then the proxy may remove the P-Early-
   Media header or alter the direction parameter(s) of the P-Early-
   Media header before forwarding the message, based on local policy.

   A proxy in the network not receiving the P-Early-Media header in a
   message towards the UAC may insert one based on local policy.

   If the proxy also performs gating of early media, then it uses the
   parameter(s) of the P-Early-Media header to decide whether to open
   or close the gates for backward and forward early media flow(s)
   between the UAs.  The proxy performing gating of early media may
   also add a "gated" parameter to the P-Early-Media header before
   forwarding the message so that other gating proxies in the path can
   choose to leave open their gates.

   If the UAC is a trusted server within the network (e.g., a PSTN
   gateway), then the UAC may use the parameter(s) of the P-Early-Media
   header in messages received from the UAS to decide whether to
   perform early media gating or cut-through and to decide whether or
   not to render backward early media in preference to generating
   ringback based on the receipt of a 180 Ringing response.

   If the UAC is associated with user equipment, then the network will
   have assigned a proxy the task of performing early media gating, so
   that the parameter(s) of the P-Early-Media header received at such a
   UAC do not require that the UAC police the early media flow(s), but
   they do provide additional information that the UAC may use to
   render media.

   The UAC and proxies in the network may also insert, delete or modify
   the P-Early-Media header in messages towards the UAS within the
   dialog according to local policy, but the interpretation of the
   header when used in this way is a matter of local policy and not
   defined herein.  The use of direction parameter(s) in this header
   could be used to inform the UAS of the final early media
   authorization status.





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7. Limitations of the P-Early-Media header

   The P-Early-Media header does not apply to any SDP with Content-
   Disposition: early-session [3].

   When parallel forking occurs, there is no reliable way to correlate
   early media authorization in a dialog with the media from the
   corresponding endpoint, since the SDP messages do not identify the
   RTP source address of any media stream.  When a UAC or proxy
   receives multiple early dialogs and cannot accurately identify the
   source of each media stream, it SHOULD use the most restrictive
   early media authorization it receives on any of the dialogs to
   decide the policy to apply towards all received media.  When early
   media usage is desired for any reason it is advisable to disable
   parallel forking using callerprefs [9].

   Although the implementation of media gating is outside the scope of
   this extension, note that media gating must be implemented carefully
   in the presence of NATs and protocols that aid in NAT traversal.
   Media gating may also introduce a potential for media clipping that
   is similar to that created during parallel forking or any other
   feature that may disable early media, such as custom ringback.


8. The P-Early-Media header

   The P-Early-Media header with no parameters MAY be included in an
   INVITE request to indicate that the UAC or a proxy on the path
   recognizes the header.

   A network entity MAY request the authorization of early media or
   change a request for authorization of early media by including the
   P-Early-Media header in any message allowed by Table 1 within the
   dialog towards the sender of the INVITE request.  The P-Early-Media
   header includes one or more direction parameters where each has one
   of the values: "sendrecv", "sendonly", "recvonly", or "inactive",
   following the convention used for Session Description Protocol (SDP)
   [7][8] stream directionality.  Each parameter applies, in order, to
   the media lines in the corresponding SDP messages establishing
   session media.  Unrecognized parameters SHALL be silently discarded.
   Non-direction parameters are ignored for purposes of early media
   authorization.  If there are more direction parameters than media
   lines, the excess SHALL be silently discarded.  If there are fewer
   direction parameters than media lines, the value of the last
   direction parameter SHALL apply to all remaining media lines.  A
   message directed towards the UAC containing a P-Early-Media header
   with no recognized direction parameters SHALL NOT be interpreted as
   an early media authorization request.




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   The parameter value "sendrecv" indicates a request for authorization
   of early media associated with the corresponding media line, both
   from the UAS towards the UAC and from the UAC towards the UAS (both
   backward and forward early media).  The value "sendonly" indicates a
   request for authorization of early media from the UAS towards the
   UAC (backward early media), and not in the other direction.  The
   value "recvonly" indicates a request for authorization of early
   media from the UAC towards the UAS (forward early media), and not in
   the other direction.  The value "inactive" indicates either a
   request that no early media associated with the corresponding media
   line be authorized, or a request for revocation of authorization of
   previously authorized early media.

   The P-Early-Media header in any message within a dialog towards the
   sender of the INVITE request MAY also include the non-direction
   parameter "gated" to indicate that a network entity on the path
   towards the UAS is already gating the early media according to the
   direction parameter(s).  When included in the P-Early-Media header,
   the "gated" parameter SHALL come after all direction parameters in
   the parameter list.

   When receiving a message directed toward the UAC without the P-
   Early-Media header and no previous early media authorization request
   has been received within the dialog, the default early media
   authorization depends on local policy and may depend on whether the
   header was included in the INVITE request.  After an early media
   authorization request has been received within a dialog and a
   subsequent message is received without the P-Early-Media header, the
   previous early media authorization remains unchanged.

   The P-Early-Media header in any message within a dialog towards the
   UAS MAY be ignored or interpreted according to local policy.

   The P-Early-Media header does not interact with SDP offer/answer
   procedures in any way.  Early media authorization is not influenced
   by the state of the SDP offer/answer procedures (including
   preconditions and directionality) and does not influence the state
   of the SDP offer/answer procedures.  The P-Early-Media header may or
   may not be present in messages containing SDP.  The most recently
   received early media authorization applies to the corresponding
   media line in the session established for the dialog until receipt
   of the 200 OK response to the INVITE request, at which point all
   media lines in the session are implicitly authorized.  Early media
   flow in a particular direction requires that early media in that
   direction is authorized, that media flow in that direction is
   enabled by the SDP direction attribute for the stream, and that any
   applicable preconditions [11] are met.  Early media authorization
   does not override the SDP direction attribute or preconditions




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   state, and the SDP direction attribute does not override early media
   authorization.

   Table 1 is an extension of Tables 2 and 3 in RFC 3261 [1] for the P-
   Early-Media header field.  The column "PRA" is for the PRACK method
   [12].  The column "UPD" is for the UPDATE method [10].


      Header field     where    proxy  ACK BYE CAN INV OPT REG PRA UPD
      ________________________________________________________________
      P-Early-Media      R       amr    -   -   -   o   -   -   o   o
      P-Early-Media     18x      amr    -   -   -   o   -   -   -   -
      P-Early-Media     2xx      amr    -   -   -   -   -   -   o   o

      Table 1: P-Early-Media Header Field


8.1. Procedures at the User Agent Client

   A User Agent Client MAY include the P-Early-Media header with no
   parameters in an INVITE request to indicate that it recognizes the
   header.

   A User Agent Client receiving a P-Early-Media header MAY use the
   parameter(s) of the header to gate or cut-through early media, and
   to decide whether to render early media from the UAS to the UAC in
   preference to any locally generated ringback triggered by a 180
   Ringing response.  If a proxy is providing the early media gating
   function for the User Agent Client, then the gateway model of RFC
   3960 [4] for rendering of early media is applicable.  A User Agent
   Client without a proxy in the network performing early media gating
   that receives a P-Early-Media header SHOULD perform gating or cut-
   through of early media according to the parameter(s) of the header.


8.2. Procedures at the User Agent Server

   A User Agent Server that is requesting authorization to send or
   receive early media MAY insert a P-Early-Media header with
   appropriate parameters(s) in any message allowed in table 1 towards
   the UAC within the dialog.  A User Agent Server MAY request changes
   in early media authorization by inserting a P-Early-Media header
   with appropriate parameter(s) in any subsequent message allowed in
   table 1 towards the UAC within the dialog.

   If the P-Early-Media header is not present in the INVITE request,
   the User Agent Server MAY choose to suppress early media
   authorization requests and MAY choose to execute alternate early
   media procedures.



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8.3. Procedures at the proxy

   When forwarding an INVITE request, a proxy MAY add, retain or delete
   the P-Early-Media header, depending on local policy and the trust
   relationship with the sender and/or receiver of the request.

   When forwarding a message allowed in table 1 towards the UAC, a
   proxy MAY add, modify or delete a P-Early-Media header, depending on
   local policy and the trust relationship with the sender and/or
   receiver of the message.  In addition, if the proxy controls the
   gating of early media for the User Agent Client, it SHOULD use the
   contents of the P-Early-Media header to gate the early media
   according to the definitions of the header parameters defined in
   clause 8.


9. Formal syntax

   The syntax of the P-Early-Media header is described below in ABNF
   according to RFC 4234 [5], as an extension to the ABNF for SIP in
   RFC 3261 [1].

      P-Early-Media = "P-Early-Media" HCOLON
                       [ em-param *(COMMA em-param) ]
      em-param      = "sendrecv" / "sendonly" / "recvonly"
                       / "inactive" / "gated" / token


10. Security Considerations

   There are no confidentiality concerns associated with the P-Early-
   Media header.  It is desirable to maintain the integrity of the
   direction parameters in the header across each hop between servers
   to avoid the potential for unauthorized use of early media.  It is
   assumed that the P-Early-Media header is used within the context of
   the 3GPP IMS trust domain or a similar trust domain, consisting of a
   collection of SIP servers maintaining pair wise security
   associations.  In an IMS it is only necessary to police the use of
   the P-Early-Media header at the boundary to user equipment served by
   the network and at the boundary to peer networks.  It is assumed
   that boundary servers in the IMS will have local policy for the
   treatment of the P-Early-Media header as it is sent to or received
   from any possible server external to the network.  Since boundary
   servers are free to modify or remove any P-Early-Media header in SIP
   messages forwarded across the boundary, the integrity of the P-
   Early-Media header can be verified to the extent that the
   connections to external servers are secured.  The authenticity of



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   the P-Early-Media header can only be assured to the extent that the
   external servers are trusted to police the authenticity of the
   header.

11. IANA Considerations

11.1. Registration of the "P-Early-Media" SIP header

   Name of Header:          P-Early-Media

   Short form:              none

   Registrant:              Richard Ejzak
                            ejzak@alcatel-lucent.com

   Normative description:   Section 8 of this document


12. Acknowledgements

   The author would like to thank Miguel Garcia-Martin, Jan Holm,
   Sebastien Garcin, Akira Kurokawa, Erick Sasaki, James Calme, Greg
   Tevonian, Aki Niemi, Paul Kyzivat, Gonzalo Camarillo and Brett Tate
   for their significant contributions made throughout the writing and
   reviewing of this document.


13. References

13.1. Normative References

   [1]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.
   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.
   [3]  Camarillo, G., "The Early Session Disposition Type for the
        Session Initiation Protocol (SIP)", RFC 3959, December 2004.
   [4]  Camarillo, G., "Early Media and Ringing Tone Generation in the
        Session Initiation Protocol (SIP)", RFC 3960, December 2004.
   [5]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
        Specifications: ABNF", RFC 4234, October 2005.
   [6]  Jennings, C., Peterson, J. and Watson, M., "Private Extensions
        to the Session Initiation Protocol (SIP) for Asserted Identity
        within Trusted Network", RFC 3325, November 2002.
   [7]  Handley, M., Jacobson, V. and Perkins, C., "SDP: Session
        Description Protocol", RFC 4566, July 2006.
   [8]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
        Session Description Protocol (SDP)", RFC 3264, June 2002.



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   [9]  Rosenberg, J., Schulzrinne, H. and Kyzivat, P., "Caller
        Preferences for the Session Initiation Protocol (SIP)", RFC
        3841, August 2004.
   [10] Rosenberg, J., "The Session Initiation Protocol (SIP) UPDATE
        Method", RFC 3311, September 2002.
   [11] Camarillo, G., Marshall, W. and Rosenberg, J., "Integration of
        Resource Management and Session Initiation Protocol (SIP)", RFC
        3312, October 2002.
   [12] Rosenberg, J. and Schulzrinne, H., "Reliability of Provisional
        Responses in the Session Initiation Protocol (SIP)", RFC 3262,
        June 2002.

13.2. Informative References

   [13] 3GPP "TS 23.228: IP Multimedia Subsystem (IMS); Stage 2
        (Release 7)", 3GPP 23.228, September 2005,
        ftp://ftp.3gpp.org/Specs/archive/23-series/23.228/.
   [14] 3GPP "TS 24.229: IP Multimedia Call Control Protocol based on
        SIP and SDP; Stage 3 (Release 7)", 3GPP 24.229, September 2005,
        ftp://ftp.3gpp.org/Specs/archive/24-series/24.229/.

   ETSI documents can be downloaded from the ETSI web server,
   http://www.etsi.org/".  Any 3GPP document can be downloaded from the
   3GPP webserver, "http://www.3gpp.org/", see specifications.


14. Authors' Addresses

   Richard Ejzak
   Alcatel-Lucent
   1960 Lucent Lane
   Naperville, IL 60566, USA

   Phone:   +1 630 979 7036
   EMail: ejzak@alcatel-lucent.com


15. IPR Notice

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed
   to pertain to the implementation or use of the technology described
   in this document or the extent to which any license under such
   rights might or might not be available; nor does it represent that
   it has made any independent effort to identify any such rights.
   Information on the procedures with respect to rights in RFC
   documents can be found in BCP 78 and BCP 79.





Ejzak                                                        [Page 13]

INTERNET-DRAFT            P-Early-Media Header        January 1, 2007


   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use
   of such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository
   at http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.


16. Copyright Notice

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on
   an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
   REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
   IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
   WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
   WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE
   ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
   FOR A PARTICULAR PURPOSE.

   This Internet-Draft expires in July 2007.


RFC Editor Considerations

   - The RFC editor is requested to replace all occurrences of XXXX
     with the RFC number this document receives.














Ejzak                                                        [Page 14]


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