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rfc:rfc3702

Network Working Group J. Loughney Request for Comments: 3702 Nokia Category: Informational G. Camarillo

                                                              Ericsson
                                                         February 2004
           Authentication, Authorization, and Accounting
       Requirements for the Session Initiation Protocol (SIP)

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2004).  All Rights Reserved.

Abstract

 As Session Initiation Protocol (SIP) services are deployed on the
 Internet, there is a need for authentication, authorization, and
 accounting of SIP sessions.  This document sets out the basic
 requirements for this work.

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
     1.1.  RADIUS . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Terminology and Acronyms . . . . . . . . . . . . . . . .  4
     1.3.  Requirements Language. . . . . . . . . . . . . . . . . .  4
 2.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Common Requirements. . . . . . . . . . . . . . . . . . .  5
           2.1.1.  Communication within the Same Domain . . . . . .  5
           2.1.2.  Communication between Different Domains. . . . .  5
           2.1.3.  Discovery. . . . . . . . . . . . . . . . . . . .  5
           2.1.4.  Ability to Integrate Different Networks,
                   Services and Users . . . . . . . . . . . . . . .  5
           2.1.5.  Updating SIP Server Entries. . . . . . . . . . .  5
           2.1.6.  SIP Session Changes. . . . . . . . . . . . . . .  5
           2.1.7.  Reliable Transfer of Protocol Messages . . . . .  5
           2.1.8.  Call Setup Times . . . . . . . . . . . . . . . .  6
           2.1.9.  Security . . . . . . . . . . . . . . . . . . . .  6
     2.2.  Authentication Requirements. . . . . . . . . . . . . . .  6
           2.2.1.  Authentication Based on SIP Requests . . . . . .  6
           2.2.2.  Flexible Authentication of SIP Requests. . . . .  6

Loughney & Camarillo Informational [Page 1] RFC 3702 AAA Requirements for SIP February 2004

     2.3.  Authorization Requirements . . . . . . . . . . . . . . .  6
           2.3.1.  Ability to Authorize SIP Requests. . . . . . . .  7
           2.3.2.  Information Transfer . . . . . . . . . . . . . .  7
           2.3.3.  User De-authorization. . . . . . . . . . . . . .  7
           2.3.4.  User Re-authorization. . . . . . . . . . . . . .  7
           2.3.5.  Support for Credit Control . . . . . . . . . . .  7
     2.4.  Accounting Requirements. . . . . . . . . . . . . . . . .  8
           2.4.1.  Separation of Accounting Information . . . . . .  8
           2.4.2.  Accounting Information Related to Session
                   Progression. . . . . . . . . . . . . . . . . . .  8
           2.4.3.  Accounting Information Not Related to Session
                   Progression. . . . . . . . . . . . . . . . . . .  9
           2.4.4.  Support for One-Time and Session-based
                   Accounting Records . . . . . . . . . . . . . . .  9
           2.4.5.  Support for Accounting on Different Media
                   Components . . . . . . . . . . . . . . . . . . .  9
           2.4.6.  Configuration of Accounting Generation
                    Parameters. . . . . . . . . . . . . . . . . . .  9
           2.4.7.  Support for Arbitrary Correlations . . . . . . .  9
 3.  Scenarios. . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  WLAN Roaming Using Third Party Service Providers . . . . 11
     3.2.  Conditional Authorization. . . . . . . . . . . . . . . . 12
 4.  Security Considerations. . . . . . . . . . . . . . . . . . . . 12
 5.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
 6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  Normative References . . . . . . . . . . . . . . . . . . 13
     6.2.  Informative References . . . . . . . . . . . . . . . . . 13
 7.  Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
 8.  Full Copyright Statement . . . . . . . . . . . . . . . . . . . 15

1. Introduction

 The AAA working group is chartered to work on authentication,
 authorization, and accounting solutions for the Internet.  This work
 consists of a base protocol, applications, end-to-end security
 application, and a general architecture for providing these services
 [3].  The AAA working group has specified applicability of AAA-based
 solutions for a number of protocols (e.g., AAA requirements for
 Mobile IP [4]).
 SIP is a signalling protocol for creating, modifying, and terminating
 different types of sessions, such as Internet phone calls, multimedia
 distribution, and multimedia conferences [1].  SIP sessions have
 needs for session authentication, authorization, and accounting
 (AAA).

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 In order to authenticate and authorize users, it is typically more
 convenient for SIP entities to communicate with an AAA sever than to
 attempt to store user credentials and profiles locally.  SIP entities
 use the SIP-AAA interface to access the AAA server.
 This document provides requirements for the interface between SIP
 entities and AAA servers.  While accounting requirements are
 discussed, this document does not cover SIP charging or billing
 mechanisms.
 One possible use of this document would be to create an AAA
 application for SIP.  Any protocol meeting the requirements outlined
 by this document could be used.  Possible candidates, among others,
 are Diameter [3] and XML-based protocols following the web-services
 model.

1.1. RADIUS

 The main purpose of this document is to provide input to designers
 working on AAA applications using new protocols, such as Diameter and
 XML-based protocols.  Nevertheless, a few limited RADIUS [5]
 extensions may meet some of the requirements in this document (for
 instance, some of the authentication requirements).  We expect that
 while RADIUS with these limited extensions will meet particular
 functional requirements, it will not meet other important
 requirements.  The following are some requirements that are not
 expected to be met by RADIUS:
    1. Section 2.1.3: RADIUS does not support a discovery feature.
    2. Section 2.1.7: RADIUS does not support reliable message
       delivery.
 The following list contains the requirements that can be met by
 RADIUS or RADIUS extensions.
    1. Section 2.1.2: Communication between domains does not scale
       well in RADIUS.  As a result, inter-domain communications are
       typically handled using a proxy architecture [6].
    2. Section 2.1.5: RADIUS clients would need to support Dynamic
       Authorization [7].
    3. Section 2.1.9: RADIUS clients would need to rely on a lower-
       layer security protocol, such as IPSec, to perform mutual
       authentication.

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    4. Section 2.3.3: RADIUS clients would need to support Dynamic
       Authorization [7].
    5. Section 2.3.4: RADIUS clients would need to support Dynamic
       Authorization [7].

1.2. Terminology and Acronyms

 AAA: Authentication, Authorization, and Accounting
 Accounting: The collection of resource consumption data for the
       purposes of capacity and trend analysis, cost allocation,
       auditing, and billing.  Accounting management requires that
       resource consumption be measured, rated, assigned, and
       communicated between appropriate parties [8].
 Accounting with credit control: The application checks the end user's
       account for coverage for the requested service event charge
       prior to execution of that service event.
 Home AAA Server: Server where user with which the user maintains an
       account relationship.
 SIP: Session Initiation Protocol
 SIP proxies: SIP proxies are nodes which forward SIP requests and
       responses, as well as make policy decisions.
 UAC: User Agent Client
 UAS: User Agent Server

1.3. Requirements Language

 In this document, the key words "MUST", "MUST NOT", "REQUIRED",
 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
 and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119
 [2].

2. Requirements

 In this section, we list the requirements.  Protocol solutions are
 not required to satisfy requirements for services that they do not
 support.  For example, a solution that provides authentication
 services but not accounting services does not need to fulfill the
 accounting requirements.  It is expected that solutions will fulfill
 the general requirements, plus the requirements for the specific
 services they are providing.

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 Section 2.1 lists general requirements, Section 2.2 lists
 requirements related to authentication, Section 2.3 lists
 requirements related to authorization, and Section 2.4 lists
 requirements related to accounting.

2.1. Common Requirements

 This section outlines general requirements on the SIP-AAA interface.

2.1.1. Communication within the Same Domain

 The SIP-AAA interface MUST support communications between a SIP
 entity and an AAA server that belong to the same domain.

2.1.2. Communication between Different Domains

 The SIP-AAA interface MUST support communications between a SIP
 entity in one domain and an AAA server in another domain.  This MAY
 involve a proxy or a redirect server architecture between both
 entities.

2.1.3. Discovery

 With the information contained in the SIP messages, the SIP-AAA
 interface SHOULD be able to deduce the particular AAA server that has
 to be queried.

2.1.4. Ability to Integrate Different Networks, Services and Users

 The basic AAA architecture MUST be access independent.  Service
 providers have to be able to provide AAA services for SIP,
 irrespective of access method or technology.

2.1.5. Updating SIP Server Entries

 When required, the SIP-AAA interface MUST allow the AAA server to
 update the information that a SIP entity has about a user.

2.1.6. SIP Session Changes

 The SIP-AAA interface MUST allow a SIP entity to inform the AAA
 server about changes in the SIP session that may affect the
 authorization, authentication, or accounting for that SIP session.

2.1.7. Reliable Transfer of Protocol Messages

 The SIP-AAA interface SHOULD provide a reliable transfer of AAA
 protocol messages between the SIP entity and the AAA server.

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2.1.8. Call Setup Times

 AAA SHOULD NOT unduly burden call setup times where appropriate.  It
 may be reasonable to support some delay during registration, but
 delay during on-going sessions (especially real-time) is problematic.

2.1.9. Security

 The SIP-AAA interface is a potential target of an attack.  An
 eavesdropper may attempt to obtain confidential data by sniffing
 messages.  Additionally, an active attacker may attempt to modify,
 insert, or replay messages between the SIP entity and the AAA server.
 Attackers may also attempt to impersonate legitimate SIP entities or
 AAA servers.
 To address these threats, the SIP-AAA interface MUST support
 confidentiality, data origin authentication, integrity, and replay
 protection.  In addition to this, bi-directional authentication
 between the SIP entity and the AAA server MUST be supported as well.

2.2. Authentication Requirements

 This section outlines requirements on the SIP-AAA interface related
 to authentication.

2.2.1. Authentication Based on SIP Requests

 The home AAA server MUST be able to authenticate a user based on any
 SIP request, except CANCELs and ACKs for non-2xx final responses.
    CANCELs and ACKs for non-2xx final responses are hop-by-hop
    requests that can be generated by proxies that do not have the
    user's credentials.

2.2.2. Flexible Authentication of SIP Requests

 The SIP-AAA interface MUST be flexible enough to accommodate a
 variety of authentication mechanisms used to authenticate SIP
 requests.  In particular, the SIP-AAA interface MUST be able to
 accommodate all the authentication mechanisms mandated by the SIP
 specifications (e.g., Digest authentication).

2.3. Authorization Requirements

 This section outlines requirements on the SIP-AAA interface related
 to authorization.

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2.3.1. Ability to Authorize SIP Requests

 The SIP-AAA interface MUST allow AAA servers to authorize any SIP
 request, except CANCELs and ACKs for non-2xx final responses.
    CANCELs and ACKs for non-2xx final responses are hop-by-hop
    requests that can be generated by proxies.  SIP servers receiving
    a CANCEL or a ACK for a non-2xx final response do not challenge
    them, as they would do with an end-to-end request.  Instead, they
    check at the transport or network layer that the entity sending
    the CANCEL or the ACK is the same as the one that generated the
    request being canceled or acked.

2.3.2. Information Transfer

 The SIP-AAA interface MUST allow transferring a wide range or set of
 information to be used to make an authorization decision.  In
 particular, the SIP-AAA interface MUST allow an AAA server that is
 making an authorization decision to deliver the user profile to the
 SIP entity.  Such a user profile may provide further information
 about the authorization decision to the SIP entity.
 For instance, a SIP proxy receives an INVITE from user A addressed to
 user B.  The SIP proxy queries an AAA server and gets the following
 answer: user A is authorized to call user B, as long as the requests
 are routed through a particular SIP proxy server C.  In this case,
 the SIP proxy needs to use SIP loose routing techniques to forward
 the INVITE so that it traverses SIP proxy C before reaching user B.

2.3.3. User De-authorization

 The SIP-AAA interface MUST allow the AAA server to inform a SIP
 entity when a particular user is no longer authorized to perform a
 particular task, even if it is an ongoing task.

2.3.4. User Re-authorization

 The SIP-AAA interface MUST allow the AAA server to inform a SIP
 entity that a particular authorization has been refreshed, and
 therefore, the user is still authorized to perform a particular task.

2.3.5. Support for Credit Control

 The SIP-AAA interface MUST support credit control.  That is, the AAA
 server has to be able to check the end user's account for coverage
 for the requested service event charge before authorizing execution
 of that service event.  Note that this requirement is related to
 accounting as well.

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 Credit control is useful to implement prepaid services where all
 chargeable events related to a specific account are withheld from the
 end user when the credit of that account is exhausted or expired.

2.4. Accounting Requirements

 This section outlines requirements on the SIP-AAA interface related
 to accounting.  Accounting is more than simple charging.  Accounting
 may be a simple list of services accessed, servers accessed, duration
 of session, etc.  Charging for SIP sessions can be extremely complex
 and requires some additional study.  It is not the intent of this
 section to focus on charging.
    The information available to be accounted is different at SIP
    proxies and at SIP UAs.  When end-to-end encryption is used,
    proxies do not have access to some parts of the SIP messages,
    while UAs have access to the whole messages.  In addition to this,
    UAs typically have information about the session itself (e.g.,
    number of audio packets exchanged during an audio session).
    Therefore, even if the SIP-AAA interface provides a means to
    transfer a wide range of data, some SIP nodes may not have access
    to it.  In order to design a network, it is important to analyze
    which SIP nodes will be able to generate the desired account
    records.

2.4.1. Separation of Accounting Information

 AAA accounting messages MUST be able to provide granular information
 based on different parameters.
 For example, it should be possible to separate "session duration"
 information from other information generated via additional services
 (e.g., 3-way calling).  Separating accounting information makes it
 possible to provide accounting information to different parties based
 upon different aspects of the session.

2.4.2. Accounting Information Related to Session Progression

 There MUST be support in the SIP-AAA interface for accounting
 transfers where the information contained in the accounting data has
 a direct bearing on the establishment, progression, and termination
 of a session (e.g., reception of a BYE request).

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2.4.3. Accounting Information Not Related to Session Progression

 There MUST be support in the SIP-AAA interface for accounting
 transfers where the information contained in the accounting data does
 NOT have a direct bearing on the establishment, progression, and
 termination of a session (e.g., an instant MESSAGE that is not
 related to any session).

2.4.4. Support for One-Time and Session-based Accounting Records

 The SIP-AAA interface MUST allow SIP servers to provide relevant
 accounting information for billing and inter-network settlement
 purposes to the AAA servers.  Both one-time event accounting records
 and session based (START, INTERIM, STOP records) accounting MUST be
 supported.

2.4.5. Support for Accounting on Different Media Components

 The SIP-AAA interface MUST support accounting per media component
 (e.g., voice and video).  That is, the SIP-AAA interface MUST be able
 to provide the AAA server with the types (e.g., voice and video) of
 the media streams of a given session.
 Note, however, that some SIP entities do not have access to this
 information, which is typically carried in session descriptions.  An
 example of a SIP entity with access to this information is a SIP UA
 (e.g., a gateway towards the PSTN).
 The SIP-AAA interface MUST enable different parties to be charged per
 media component.

2.4.6. Configuration of Accounting Generation Parameters

 The SIP-AAA interface MUST allow AAA servers to communicate
 parameters for accounting generation.

2.4.7. Support for Arbitrary Correlations

 Some networks need to be able to relate accounting information to
 some aspect of the SIP messages involved.  So, the SIP-AAA interface
 MUST allow the AAA server to correlate a particular AAA session with
 any aspect of the SIP messages.  For example, an AAA server that
 receives accounting information about a SIP dialog may be interested
 in knowing the Call-ID of the SIP dialog.

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3. Scenarios

 This section outlines some possible scenarios for SIP and AAA
 interaction.  These are purely illustrative examples and do not
 impose any requirements.
 Figure 1 shows the typical call flow between a SIP proxy that
 communicates to an AAA server that performs authentication and
 authorization.  All the examples are based on this flow.
        SIP            SIP            AAA
        UAC           Proxy          Server
         |              |              |
         |---METHOD---->|              |
         |              |--Is it OK?-->|
         |              |              |
         |              |<-----OK------|
         |              |              |
         |              |              |
 Figure 1: Call flow over the SIP-AAA interface
 The SIP proxy receives a request with certain credentials.  The SIP
 UAC that generated the request may have included the credentials
 after having been challenged by the proxy using a 407 (Proxy
 Authentication Required) response.  The SIP proxy sends a request to
 the AAA server asking if it is OK to provide a particular service for
 this request.  The service may be simply routing forward the request
 or may consist of a more complex service.  The AAA server checks that
 the credentials are correct (authentication), and checks the user
 profile.  The user profile indicates that it is OK to provide the
 service, and responds to the SIP proxy.  The SIP proxy provides the
 service requested by the SIP UAC.

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3.1. WLAN Roaming Using Third Party Service Providers

 User A wants to establish a voice session over the Internet with user
 B.  User A wants its SIP signalling to be routed through SIP proxy C,
 because it provides a call log service (i.e., SIP proxy C sends an
 email to user A once a month with the duration of all the calls made
 during the month).
                        SIP               AAA
      User A          Proxy C            Server           User B
        |                |                 |                |
        |----INVITE----->|                 |                |
        |                |                 |                |
        |<-----407-------|                 |                |
        |                |                 |                |
        |------ACK------>|                 |                |
        |                |                 |                |
        |----INVITE----->|                 |                |
        |                |---Is this OK?-->|                |
        |                |                 |                |
        |                |<------OK--------|                |
        |                |                 |                |
        |                |---------INVITE------------------>|
        |                |                 |                |
        |                |-Accounting msg->|                |
        |                |                 |                |
 Figure 2: WLAN roaming user
 User A accesses the Internet using a WLAN access outside his home
 domain.  User A, user B, SIP proxy C, and the home AAA server of user
 A are all in different domains.
 SIP proxy C challenges the initial INVITE from user A with a 407
 (Proxy Authentication Required) response, and user A reissues the
 INVITE including his credentials.  SIP proxy C consults user A's home
 AAA server, which confirms that the credentials belong to user A and
 that SIP proxy C can go ahead and provide its service for that call.
 SIP proxy C routes the INVITE forward towards user B and sends an
 accounting message to the AAA server, which will be used later to
 charge user A for the service provided by SIP proxy C.

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3.2. Conditional Authorization

 User A is not in his home domain, but he still uses SIP proxy C
 (which is in user's A home domain) as the outbound proxy for an
 INVITE.  SIP proxy C consults the home AAA server, which indicates
 that requests from user A have to be routed through SIP proxy D.  SIP
 proxy C uses SIP loose routing so that the INVITE traverses D before
 reaching its destination.  SIP proxy D will provide a call log
 service for user A.
                        SIP                    AAA         SIP
      User A          Proxy C                 Server     Proxy D
        |                |                      |           |
        |----INVITE----->|                      |           |
        |                |                      |           |
        |<-----407-------|                      |           |
        |                |                      |           |
        |------ACK------>|                      |           |
        |                |                      |           |
        |----INVITE----->|                      |           |
        |                |------Is this OK?---->|           |
        |                |                      |           |
        |                |<-OK if routed thru D-|           |
        |                |                      |           |
        |                |---------INVITE------------------>|
        |                |                      |           |
 Figure 3: Conditional Authorization

4. Security Considerations

 Security is a critical requirement of the SIP-AAA Interface.  Section
 2.1.9 describes the threats and security requirements.  Sections 2.2
 and 2.3 elaborate on the authentication and authorization
 requirements.

5. Acknowledgements

 The authors would like to thank the participants of the SIP interim
 meeting, May 2002 for their comments.  The authors would also thank
 Harri Hakala, Mary Barns, Pete McCann, Jari Arkko, Aki Niemi, Juha
 Heinanen, Henry Sinnreich, Allison Mankin, and Bernard Aboba for
 their comments.
 The authors would like to thank the authors of the "AAA Requirements
 for IP Telephony/Multimedia" document, as it provided a basis for
 some of the information contained in this document.

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6. References

6.1. 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.

6.2. Informative References

 [3] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J. Arkko,
     "Diameter Base Protocol", RFC 3588, September 2003.
 [4] Glass, S., Hiller, T., Jacobs, S. and C. Perkins, "Mobile IP
     Authentication, Authorization, and Accounting Requirements", RFC
     2977, October 2000.
 [5] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
     Authentication Dial in User Service (RADIUS)", RFC 2865, June
     2000.
 [6] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
     Implementation in Roaming", RFC 2607, June 1999.
 [7] Chiba, M., Dommety, G., Eklund, M., Mitton, D. and B. Aboba,
     "Dynamic Authorization Extensions to Remote Authentication Dial
     in User Service (RADIUS)", RFC 3576, July 2003.
 [8] Aboba, B., Arkko, J. and D. Harrington, "Introduction to
     Accounting Management", RFC 2975, October 2000.

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7. Authors' Addresses

 John Loughney
 Nokia
 Itamerenkatu 11-13
 00180 Helsinki
 Finland
 EMail:  John.Loughney@nokia.com
 Gonzalo Camarillo
 Ericsson
 Advanced Signalling Research Lab.
 FIN-02420 Jorvas
 Finland
 EMail:  Gonzalo.Camarillo@ericsson.com

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8. Full Copyright Statement

 Copyright (C) The Internet Society (2004).  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 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.

Intellectual Property

 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.
 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.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

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