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Versions: 00 01 02 03 04 rfc3702                                        
Internet Engineering Task Force                                   SIP WG
Internet Draft                                               J. Loughney
                                                                   Nokia
                                                            G. Camarillo
                                                                Ericsson
draft-ietf-sipping-aaa-req-00.txt
September 10, 2002
Expires: March 2003


       Authentication, Authorization and Accounting Requirements
                  for the Session Initiation Protocol

STATUS OF THIS MEMO

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   To view the list Internet-Draft Shadow Directories, see
   http://www.ietf.org/shadow.html.


Abstract

   As 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.












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                           Table of Contents



   1          Introduction ........................................    4
   1.1        Scope of This Document ..............................    4
   1.2        Terminology .........................................    4
   1.3        Requirements Language ...............................    5
   2          Requirements ........................................    5
   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 ......................................................    6
   2.1.5      Updating SIP Server Entries .........................    6
   2.1.6      Call Setup Times ....................................    6
   2.1.7      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
   2.3        Authorization Requirements ..........................    7
   2.3.1      Ability to Authorize SIP Registration ...............    7
   2.3.2      Information transfer ................................    7
   2.3.3      Distribution of Profiles ............................    7
   2.3.4      User De-authorization ...............................    7
   2.4        Accounting Requirements .............................    7
   2.4.1      Separation of Accounting Information ................    7
   2.4.2      Accounting Information Related to Session
   Progression ....................................................    8
   2.4.3      Accounting Information Not Related to Session
   Progression ....................................................    8
   2.4.4      Support for One-Time and Session-based Accounting
   Records ........................................................    8
   2.4.5      SIP Session Changes .................................    8
   2.4.6      Support for Accounting on Different Media
   Components .....................................................    8
   2.4.7      Support for Stateful and Stateless Accounting .......    8
   2.4.8      Configuration of Accounting Generation Parameters
   ................................................................    8
   2.4.9      Support for Arbitrary Correlation IDs ...............    8
   2.4.10     Support of Credit-based Charging ....................    9
   2.4.11     Flexible Interface ..................................    9
   3          Scenarios ...........................................    9
   3.1        WLAN Roaming Using Third Party Service Providers.....   10



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   3.2        Simple 3GPP Example .................................   11
   4          Security Considerations .............................   12
   5          Acknowledgements ....................................   12
   6          Authors' Addresses ..................................   12
   7          Normative References ................................   12
   8          Informative References ..............................   12













































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1 Introduction

   The AAA working group is chartered to work on authentication,
   authorization and accounting solutions for the Internet, which
   consists of a base protocol, applications, end-to-end security
   application and a general architecture for providing these services
   [3].

   The applicability of AAA-based solutions for a number of protocols
   have been specified, for example the AAA requirements for Mobile IP
   [4].

   SIP provides a signaling protocol for creating, modifying and
   terminating different types sessions such as Internet phone calls,
   multimedia distribution and multimedia conferences [1].

1.1 Scope of This Document

   SIP sessions have needs for session authentication, authorization and
   accounting. In order to perform AAA, SIP entities need to access AAA
   information (e.g., check if the password provided by a user is
   correct or store accounting records related to a particular session).
   Rather than collocating a database with AAA information with every
   SIP entity in a network, it is desirable to have a common logical AAA
   server accessible by all the SIP entities. SIP entities use a SIP-AAA
   interface to access this AAA server. This document outlines some
   requirements on this SIP-AAA interface between SIP entities and AAA
   servers. This document is intended as a generic document for SIP AAA
   requirements. It does not intend to develop a charging and/or billing
   mechanism for SIP.

   One possible use of this document would be to create a basic AAA
   application for SIP needs. The protocol used in the SIP-AAA interface
   could be any protocol that meets the requirements outlined by this
   document. Possible candidates, among others, are Diameter and XML-
   based protocols following the web-services model.

1.2 Terminology

        AAA: Authentication, Authorization and Accounting

        Accounting: In this draft, accounting is meant in a broad sense,
             not simply charging or billing.

        Home AAA Server: Server where user with which the user maintains
             an account relationship.

        Online Accounting: Downloading some kind of credit into the



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             access device, and deducting from that credit as usage
             accumulates.

        Offline Accounting: Transferring records to a home accounting
             server, for later billing and settlement, without doing any
             accounting-related control or feedback for the services
             rendered.

        SIP: Session Initiation Protocol

        UAC: User Agent Client

        UAS: User Agent Server

        Proxies: Proxies are nodes which forward requests and responses
             as well as make policy decisions.

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 RFC 2119 [2].

2 Requirements

   In this section, we list the requirements. It is assumed that
   different situations, deployment scenarios will affect which
   requirements are needed. It is not intended that all requirements
   need to be supported. 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 a 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 a AAA server in another domain.

2.1.3 Discovery



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   With the information contained in the SIP messages, the SIP-AAA
   interface MUST be able to deduct 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 about a user that a SIP entity has.

2.1.6 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 sessions (especially real-time) are problematic.

2.1.7 Security

   AAA data MUST be able to be securely transported. The endpoints MUST
   be authenticated before data is sent. The endpoints MAY be authorized
   to access certain types of AAA data.

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 CANCEL.

        CANCEL is a hop-by-hop request that can be generated by
        proxies. SIP servers receiving a CANCEL do not challenge
        it, as they would do with an end-to-end request. Instead,
        they check that the entity sending the CANCEL is the same
        as the one that generated the request being canceled.

2.2.2 Flexible Authentication of SIP requests

   The scheme supported for the authentication between the SIP servers
   and the AAA infrastructure MUST be flexible enough to accommodate a
   variety of authentication mechanisms.



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2.3 Authorization Requirements

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

2.3.1 Ability to Authorize SIP Registration

   The SIP-AAA interface MUST allow AAA servers to authorize any SIP
   request, except CANCEL.

2.3.2 Information transfer

   The SIP-AAA interface MUST allow transfering a wide range or set of
   information to be used to make an authorization decision.

2.3.3 Distribution of Profiles

   The SIP-AAA interface MUST allow a AAA server that is making an
   authorization decision to deliver the user profile to the SIP entity.
   Note that the 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 a 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.

2.3.4 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.

2.4 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.

2.4.1 Separation of Accounting Information

   AAA accounting messages MUST be able to separate "session duration"
   information from other information generated via additional services
   (e.g., 3-way calling, etc.)



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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.

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.

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
   purpose to the AAA servers. Both one-time event accounting records
   and session based (START, INTERIM, STOP records) accounting MUST be
   supported.

2.4.5 SIP Session Changes

   Accounting messages MUST be able to reflect changes in the SIP
   session that affects the charging of SIP session.

2.4.6 Support for Accounting on Different Media Components

   The SIP-AAA interface MUST support accounting per media component
   (e.g., voice and video). The SIP-AAA interface MUST enable different
   parties to be charged per media component.

2.4.7 Support for Stateful and Stateless Accounting

   Stateful and stateless accounting MUST be supported by the SIP-AAA
   interface.

2.4.8 Configuration of Accounting Generation Parameters

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

2.4.9 Support for Arbitrary Correlation IDs

   Some networks need to be able to relate the accounting to some aspect
   of the session. Therefore, the SIP-AAA interface MUST support
   arbitrary correlation IDs.



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2.4.10 Support of Credit-based Charging

   The SIP-AAA interface MUST support credit-based charging. The
   accounting application has to be able to check the end user's account
   for coverage for the requested service event charge prior to
   execution of that service event. All the chargeable events related to
   a specific account need to be prevented from the end user when the
   credit of that account is exhausted or expired.

2.4.11 Flexible Interface

   The scheme supported for the accounting between the SIP servers and
   the AAA infrastructure MUST be flexible enough to accommodate a
   variety of accounting mechanisms.

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 a 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



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   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.

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.



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   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's A 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.

3.2 Simple 3GPP Example

   User A is not in his home domain, but it 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 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: 3GPP example



   The example in figure 3 illustrates roughly how a SIP based 3GPP
   network works.




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4 Security Considerations

   This document is informational in nature, so it does not directly
   affect the security of the Internet. However, security is a basic
   requirement of this work.

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
   Mary Barns, Pete McCann and Henry Sinnreich for their comments.

   The authors would like to thank the authors of the "AAA Requirements
   for IP Telephony/Multimedia" draft, which some of the information in
   this document is based on.

6 Authors' Addresses

   John Loughney
   Nokia Research Center
   Itmerenkatu 11-13
   00180 Helsinki
   Finland
   electronic mail:  john.Loughney@nokia.com

   Gonzalo Camarillo
   Ericsson
   Advanced Signalling Research Lab.
   FIN-02420 Jorvas
   Finland
   electronic mail:  Gonzalo.Camarillo@ericsson.com

7 Normative References

   [1] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
   Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session
   initiation protocol," RFC 3261, Internet Engineering Task Force, June
   2002.

   [2] S. Bradner, "Key words for use in RFCs to indicate requirement
   levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.

8 Informative References

   [3] P. Calhoun  et al.  , "AAA problem statements," Internet Draft,
   Internet Engineering Task Force, Nov. 2000.  Work in progress.

   [4] S. Glass, T. Hiller, S. Jacobs, and C. Perkins, "Mobile IP



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   authentication, authorization, and accounting requirements," RFC
   2977, Internet Engineering Task Force, Oct. 2000.


   Full Copyright Statement

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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.




















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