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rfc:rfc4745

Network Working Group H. Schulzrinne Request for Comments: 4745 Columbia U. Category: Standards Track H. Tschofenig

                                         Siemens Networks GmbH & Co KG
                                                             J. Morris
                                                                   CDT
                                                            J. Cuellar
                                                               Siemens
                                                               J. Polk
                                                          J. Rosenberg
                                                                 Cisco
                                                         February 2007
Common Policy: A Document Format for Expressing Privacy Preferences

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 This document defines a framework for authorization policies
 controlling access to application-specific data.  This framework
 combines common location- and presence-specific authorization
 aspects.  An XML schema specifies the language in which common policy
 rules are represented.  The common policy framework can be extended
 to other application domains.

Schulzrinne, et al. Standards Track [Page 1] RFC 4745 Common Policy February 2007

Table of Contents

 1. Introduction ....................................................3
 2. Terminology .....................................................4
 3. Modes of Operation ..............................................4
    3.1. Passive Request-Response - PS as Server (Responder) ........5
    3.2. Active Request-Response - PS as Client (Initiator) .........5
    3.3. Event Notification .........................................5
 4. Goals and Assumptions ...........................................6
 5. Non-Goals .......................................................7
 6. Basic Data Model and Processing .................................8
    6.1. Identification of Rules ....................................9
    6.2. Extensions .................................................9
 7. Conditions .....................................................10
    7.1. Identity Condition ........................................10
         7.1.1. Overview ...........................................10
         7.1.2. Matching One Entity ................................11
         7.1.3. Matching Multiple Entities .........................11
    7.2. Single Entity .............................................14
    7.3. Sphere ....................................................15
    7.4. Validity ..................................................16
 8. Actions ........................................................17
 9. Transformations ................................................18
 10. Procedure for Combining Permissions ...........................18
    10.1. Introduction .............................................18
    10.2. Combining Rules (CRs) ....................................18
    10.3. Example ..................................................19
 11. Meta Policies .................................................21
 12. Example .......................................................21
 13. XML Schema Definition .........................................22
 14. Security Considerations .......................................25
 15. IANA Considerations ...........................................25
    15.1. Common Policy Namespace Registration .....................25
    15.2. Content-type Registration for
          'application/auth-policy+xml' ............................26
    15.3. Common Policy Schema Registration ........................27
 16. References ....................................................27
    16.1. Normative References .....................................27
    16.2. Informative References ...................................28
 Appendix A. Contributors ..........................................29
 Appendix B. Acknowledgments .......................................29

Schulzrinne, et al. Standards Track [Page 2] RFC 4745 Common Policy February 2007

1. Introduction

 This document defines a framework for creating authorization policies
 for access to application-specific data.  This framework is the
 result of combining the common aspects of single authorization
 systems that more specifically control access to presence and
 location information and that previously had been developed
 separately.  The benefit of combining these two authorization systems
 is two-fold.  First, it allows building a system that enhances the
 value of presence with location information in a natural way and
 reuses the same underlying authorization mechanism.  Second, it
 encourages a more generic authorization framework with mechanisms for
 extensibility.  The applicability of the framework specified in this
 document is not limited to policies controlling access to presence
 and location information data, but can be extended to other
 application domains.
 The general framework defined in this document is intended to be
 accompanied and enhanced by application-specific policies specified
 elsewhere.  The common policy framework described here is enhanced by
 domain-specific policy documents, including presence [7] and location
 [8].  This relationship is shown in Figure 1.
                         +-----------------+
                         |                 |
                         |     Common      |
                         |     Policy      |
                         |                 |
                         +---+---------+---+
                            /|\       /|\
                             |         |
    +-------------------+    |         |    +-------------------+
    |                   |    | enhance |    |                   |
    | Location-specific |    |         |    | Presence-specific |
    |      Policy       |----+         +----|      Policy       |
    |                   |                   |                   |
    +-------------------+                   +-------------------+
                 Figure 1: Common Policy Enhancements
 This document starts with an introduction to the terminology in
 Section 2, an illustration of basic modes of operation in Section 3,
 a description of goals (see Section 4) and non-goals (see Section 5)
 of the policy framework, followed by the data model in Section 6.
 The structure of a rule, namely, conditions, actions, and
 transformations, is described in Sections 7, 8, and 9.  The procedure
 for combining permissions is explained in Section 10 and used when
 conditions for more than one rule are satisfied.  A short description

Schulzrinne, et al. Standards Track [Page 3] RFC 4745 Common Policy February 2007

 of meta policies is given in Section 11.  An example is provided in
 Section 12.  The XML schema will be discussed in Section 13.  IANA
 considerations in Section 15 follow security considerations in
 Section 14.

2. Terminology

 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 [1].
 This document introduces the following terms:
 PT - Presentity / Target:  The PT is the entity about whom
      information has been requested.
 RM - Rule Maker:  The RM is an entity that creates the authorization
      rules that restrict access to data items.
 PS - (Authorization) Policy Server:  This entity has access to both
      the authorization policies and the data items.  In location-
      specific applications, the entity PS is labeled as location
      server (LS).
 WR - Watcher / Recipient:  This entity requests access to data items
      of the PT.  An access operation might be a read, a write, or any
      other operation.
 A policy is given by a 'rule set' that contains an unordered list of
 'rules'.  A 'rule' has a 'conditions', an 'actions', and a
 'transformations' part.
 The term 'permission' indicates the action and transformation
 components of a 'rule'.
 The term 'using protocol' is defined in [9].  It refers to the
 protocol used to request access to and to return privacy-sensitive
 data items.

3. Modes of Operation

 The abstract sequence of operations can roughly be described as
 follows.  The PS receives a query for data items for a particular PT,
 via the using protocol.  The using protocol (or more precisely, the
 authentication protocol) provides the identity of the requestor,
 either at the time of the query or at the subscription time.  The
 authenticated identity of the WR, together with other information
 provided by the using protocol or generally available to the server,

Schulzrinne, et al. Standards Track [Page 4] RFC 4745 Common Policy February 2007

 is then used for searching through the rule set.  All matching rules
 are combined according to a permission combining algorithm described
 in Section 10.  The combined rules are applied to the application
 data, resulting in the application of privacy based on the
 transformation policies.  The resulting application data is returned
 to the WR.
 Three different modes of operation can be distinguished:

3.1. Passive Request-Response - PS as Server (Responder)

 In a passive request-response mode, the WR queries the PS for data
 items about the PT.  Examples of protocols following this mode of
 operation include HTTP, FTP, LDAP, finger, and various remote
 procedure call (RPC) protocols, including Sun RPC, Distributed
 Computing Environment (DCE), Distributed Component Object Model
 (DCOM), common object request broker architecture (Corba), and Simple
 Object Access Protocol (SOAP).  The PS uses the rule set to determine
 whether the WR is authorized to access the PT's information, refusing
 the request if necessary.  Furthermore, the PS might filter
 information by removing elements or by reducing the resolution of
 elements.

3.2. Active Request-Response - PS as Client (Initiator)

 Alternatively, the PS may contact the WR and convey data items.
 Examples include HTTP, SIP session setup (INVITE request), H.323
 session setup or SMTP.

3.3. Event Notification

 Event notification adds a subscription phase to the "Active Request-
 Response - PS as Client (Initiator)" mode of operation.  A watcher or
 subscriber asks to be added to the notification list for a particular
 presentity or event.  When the presentity changes state or the event
 occurs, the PS sends a message to the WR containing the updated
 state.  (Presence is a special case of event notification; thus, we
 often use the term interchangeably.)
 In addition, the subscriber may itself add a filter to the
 subscription, limiting the rate or content of the notifications.  If
 an event, after filtering by the rule-maker-provided rules and by the
 subscriber-provided rules, only produces the same notification
 content that was sent previously, no event notification is sent.

Schulzrinne, et al. Standards Track [Page 5] RFC 4745 Common Policy February 2007

 A single PS may authorize access to data items in more than one mode.
 Rather than having different rule sets for different modes all three
 modes are supported with a one rule set schema.  Specific instances
 of the rule set can omit elements that are only applicable to the
 subscription model.

4. Goals and Assumptions

 Below, we summarize our design goals and constraints.
 Table representation:
    Each rule must be representable as a row in a relational database.
    This design goal should allow efficient policy implementation by
    utilizing standard database optimization techniques.
 Permit only:
    Rules only provide permissions rather than denying them.  Removing
    a rule can never increase permissions.  Depending on the
    interpretation of 'deny' and 'permit' rules, the ordering of rules
    might matter, making updating rule sets more complicated since
    such update mechanisms would have to support insertion at specific
    locations in the rule set.  Additionally, it would make
    distributed rule sets more complicated.  Hence, only 'permit'
    actions are allowed that result in more efficient rule processing.
    This also implies that rule ordering is not important.
    Consequently, to make a policy decision requires processing all
    rules.
 Additive permissions:
    A query for access to data items is matched against the rules in
    the rule database.  If several rules match, then the overall
    permissions granted to the WR are the union of those permissions.
    A more detailed discussion is provided in Section 10.
 Upgradeable:
    It should be possible to add additional rules later, without
    breaking PSs that have not been upgraded.  Any such upgrades must
    not degrade privacy constraints, but PSs not yet upgraded may
    reveal less information than the rule maker would have chosen.

Schulzrinne, et al. Standards Track [Page 6] RFC 4745 Common Policy February 2007

 Capability support:
    In addition to the previous goal, a RM should be able to determine
    which extensions are supported by the PS.  The mechanism used to
    determine the capability of a PS is outside the scope of this
    specification.
 Protocol-independent:
    The rule set supports constraints on both notifications or queries
    as well as subscriptions for event-based systems such as presence
    systems.
 No false assurance:
    It appears more dangerous to give the user the impression that the
    system will prevent disclosure automatically, but fail to do so
    with a significant probability of operator error or
    misunderstanding, than to force the user to explicitly invoke
    simpler rules.  For example, rules based on weekday and time-of-
    day ranges seem particularly subject to misinterpretation and
    false assumptions on part of the RM.  (For example, a non-
    technical RM would probably assume that the rules are based on the
    time zone of his current location, which may not be known to other
    components of the system.)

5. Non-Goals

 We explicitly decided that a number of possibly worthwhile
 capabilities are beyond the scope of this first version.  Future
 versions may include these capabilities, using the extension
 mechanism described in this document.  Non-goals include:
 No external references:
    Attributes within specific rules cannot refer to external rule
    sets, databases, directories, or other network elements.  Any such
    external reference would make simple database implementation
    difficult and hence they are not supported in this version.
 No regular expressions:
    Conditions are matched on equality or 'greater-than'-style
    comparisons, not regular expressions, partial matches such as the
    SQL LIKE operator (e.g., LIKE "%foo%"), or glob-style matches
    ("*@example.com").  Most of these are better expressed as explicit
    elements.

Schulzrinne, et al. Standards Track [Page 7] RFC 4745 Common Policy February 2007

 No repeat times:
    Repeat times (e.g., every day from 9 am to 4 pm) are difficult to
    make work correctly, due to the different time zones that PT, WR,
    PS, and RM may occupy.  It appears that suggestions for including
    time intervals are often based on supporting work/non-work
    distinctions, which unfortunately are difficult to capture by time
    alone.  Note that this feature must not be confused with the
    'Validity' element that provides a mechanism to restrict the
    lifetime of a rule.

6. Basic Data Model and Processing

 A rule set (or synonymously, a policy) consists of zero or more
 rules.  The ordering of these rules is irrelevant.  The rule set can
 be stored at the PS and conveyed from RM to PS as a single document,
 in subsets or as individual rules.  A rule consists of three parts:
 conditions (see Section 7), actions (see Section 8), and
 transformations (see Section 9).
 The conditions part is a set of expressions, each of which evaluates
 to either TRUE or FALSE.  When a WR asks for information about a PT,
 the PS goes through each rule in the rule set.  For each rule, it
 evaluates the expressions in the conditions part.  If all of the
 expressions evaluate to TRUE, then the rule is applicable to this
 request.  Generally, each expression specifies a condition based on
 some variable that is associated with the context of the request.
 These variables can include the identity of the WR, the domain of the
 WR, the time of day, or even external variables, such as the
 temperature or the mood of the PT.
 Assuming that the rule is applicable to the request, the actions and
 transformations (commonly referred to as permissions) in the rule
 specify how the PS is supposed to handle this request.  If the
 request is to view the location of the PT, or to view its presence,
 the typical action is "permit", which allows the request to proceed.
 Assuming the action allows the request to proceed, the
 transformations part of the rule specifies how the information about
 the PT -- their location information, their presence, etc. -- is
 modified before being presented to the WR.  These transformations are
 in the form of positive permissions.  That is, they always specify a
 piece of information that is allowed to be seen by the WR.  When a PS
 processes a request, it takes the transformations specified across
 all rules that match, and creates the union of them.  For computing
 this union, the data type, such as Integer, Boolean, Set, or the
 Undef data type, plays a role.  The details of the algorithm for
 combining permissions is described in Section 10.  The resulting

Schulzrinne, et al. Standards Track [Page 8] RFC 4745 Common Policy February 2007

 union effectively represents a "mask" -- it defines what information
 is exposed to the WR.  This mask is applied to the actual location or
 presence data for the PT, and the data that is permitted by the mask
 is shown to the WR.  If the WR requests a subset of information only
 (such as city-level civic location data only, instead of the full
 civic location information), the information delivered to the WR MUST
 be the intersection of the permissions granted to the WR and the data
 requested by the WR.
 Rules are encoded in XML.  To this end, Section 13 contains an XML
 schema defining the Common Policy Markup Language.  This, however, is
 purely an exchange format between RM and PS.  The format does not
 imply that the RM or the PS use this format internally, e.g., in
 matching a query with the policy rules.  The rules are designed so
 that a PS can translate the rules into a relational database table,
 with each rule represented by one row in the database.  The database
 representation is by no means mandatory; we will use it as a
 convenient and widely-understood example of an internal
 representation.  The database model has the advantage that operations
 on rows have tightly defined meanings.  In addition, it appears
 plausible that larger-scale implementations will employ a backend
 database to store and query rules, as they can then benefit from
 existing optimized indexing, access control, scaling, and integrity
 constraint mechanisms.  Smaller-scale implementations may well choose
 different implementations, e.g., a simple traversal of the set of
 rules.

6.1. Identification of Rules

 Each rule is equipped with a parameter that identifies the rule.
 This rule identifier is an opaque token chosen by the RM.  A RM MUST
 NOT use the same identifier for two rules that are available to the
 PS at the same time for a given PT.  If more than one RM modifies the
 same rule set, then it needs to be ensured that a unique identifier
 is chosen for each rule.  A RM can accomplish this goal by retrieving
 the already specified rule set and choosing a new identifier for a
 rule that is different from the existing rule set.

6.2. Extensions

 The policy framework defined in this document is meant to be
 extensible towards specific application domains.  Such an extension
 is accomplished by defining conditions, actions, and transformations
 that are specific to the desired application domain.  Each extension
 MUST define its own namespace.

Schulzrinne, et al. Standards Track [Page 9] RFC 4745 Common Policy February 2007

 Extensions cannot change the schema defined in this document, and
 this schema is not expected to change except via revision to this
 specification.  Therefore, no versioning procedures for this schema
 or namespace are provided.

7. Conditions

 The access to data items needs to be matched with the rule set stored
 at the PS.  Each instance of a request has different attributes
 (e.g., the identity of the requestor) that are used for
 authorization.  A rule in a rule set might have a number of
 conditions that need to be met before executing the remaining parts
 of a rule (i.e., actions and transformations).  Details about rule
 matching are described in Section 10.  This document specifies only a
 few conditions (i.e., identity, sphere, and validity).  Further
 condition elements can be added via extensions to this document.  If
 a child element of the <conditions> element is in a namespace that is
 not known or not supported, then this child element evaluates to
 FALSE.
 As noted in Section 5, conditions are matched on equality or "greater
 than" style comparisons, rather than regular expressions.  Equality
 is determined according to the rules for the data type associated
 with the element in the schema given in Section 13, unless explicit
 comparison steps are included in this document.  For xs:anyURI types,
 readers may wish to consult [2] for its discussion xs:anyURI, as well
 as the text in Section 13.

7.1. Identity Condition

7.1.1. Overview

 The identity condition restricts matching of a rule either to a
 single entity or a group of entities.  Only authenticated entities
 can be matched; acceptable means of authentication are defined in
 protocol-specific documents.  If the <identity> element is absent,
 identities are not considered, and thus, other conditions in the rule
 apply to any user, authenticated or not.
 The <identity> condition is considered TRUE if any of its child
 elements (e.g., the <one/> and the <many/> elements defined in this
 document) evaluate to TRUE, i.e., the results of the individual child
 element are combined using a logical OR.
 If a child element of the <identity> element is in a namespace that
 is not known or not supported, then this child element evaluates to
 FALSE.

Schulzrinne, et al. Standards Track [Page 10] RFC 4745 Common Policy February 2007

7.1.2. Matching One Entity

 The <one> element matches the authenticated identity (as contained in
 the 'id' attribute) of exactly one entity or user.  For
 considerations regarding the 'id' attribute, refer to Section 7.2.
 An example is shown below:
 <?xml version="1.0" encoding="UTF-8"?>
 <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
     <rule id="f3g44r1">
         <conditions>
             <identity>
                 <one id="sip:alice@example.com"/>
                 <one id="tel:+1-212-555-1234" />
                 <one id="mailto:bob@example.net" />
             </identity>
         </conditions>
         <actions/>
         <transformations/>
     </rule>
 </ruleset>
 This example matches if the authenticated identity of the WR is
 either sip:alice@example.com, tel:+1-212-555-1234, or
 mailto:bob@example.net.

7.1.3. Matching Multiple Entities

 The <many> element is a mechanism to perform authorization decisions
 based on the domain part of the authenticated identity.  As such, it
 allows matching a large and possibly unknown number of users within a
 domain.
 Furthermore, it is possible to include one or multiple <except>
 elements to exclude either individual users or users belonging to a
 specific domain.  Excluding individual entities is implemented using
 a <except id="..."/> statement.  The semantic of the 'id' attribute
 of the <except> element has the same meaning as the 'id' attribute of
 the <one> element (see Section 7.2).  Excluding users belonging to a
 specific domain is implemented using the <except domain="..."/>
 element that excludes any user from the indicated domain.
 If multiple <except> elements are listed as child elements of the
 <many> element, then the result of each <except> element is combined
 using a logical OR.

Schulzrinne, et al. Standards Track [Page 11] RFC 4745 Common Policy February 2007

 Common policy MUST either use UTF-8 or UTF-16 to store domain names
 in the 'domain' attribute.  For non-IDNs (Internationalized Domain
 Names), lowercase ASCII SHOULD be used.  For the comparison operation
 between the value stored in the 'domain' attribute and the domain
 value provided via the using protocol (referred to as "protocol
 domain identifier"), the following rules are applicable:
 1.  Translate percent-encoding for either string.
 2.  Convert both domain strings using the ToASCII operation described
     in RFC 3490 [3].
 3.  Compare the two domain strings for ASCII equality, for each
     label.  If the string comparison for each label indicates
     equality, the comparison succeeds.  Otherwise, the domains are
     not equal.
 If the conversion fails in step (2), the domains are not equal.

7.1.3.1. Matching Any Authenticated Identity

 The <many/> element without any child elements or attributes matches
 any authenticated user.
 The following example shows such a rule that matches any
 authenticated user:
 <?xml version="1.0" encoding="UTF-8"?>
 <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
     <rule id="f3g44r5">
         <conditions>
             <identity>
               <many/>
             </identity>
         </conditions>
         <actions/>
         <transformations/>
     </rule>
 </ruleset>

Schulzrinne, et al. Standards Track [Page 12] RFC 4745 Common Policy February 2007

7.1.3.2. Matching Any Authenticated Identity Except Enumerated

        Domains/Identities
 The <many> element enclosing one or more <except domain="..."/>
 elements matches any user from any domain except those enumerated.
 The <except id="..."/> element excludes particular users.  The
 semantics of the 'id' attribute of the <except> element is described
 in Section 7.2.  The results of the child elements of the <many>
 element are combined using a logical OR.
 An example is shown below:
 <?xml version="1.0" encoding="UTF-8"?>
 <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
     <rule id="f3g44r1">
         <conditions>
             <sphere value="work"/>
             <identity>
                 <many>
                     <except domain="example.com"/>
                     <except domain="example.org"/>
                     <except id="sip:alice@bad.example.net"/>
                     <except id="sip:bob@good.example.net"/>
                     <except id="tel:+1-212-555-1234" />
                     <except id="sip:alice@example.com"/>
                 </many>
             </identity>
             <validity>
                 <from>2003-12-24T17:00:00+01:00</from>
                 <until>2003-12-24T19:00:00+01:00</until>
             </validity>
         </conditions>
         <actions/>
         <transformations/>
     </rule>
 </ruleset>
 This example matches all users except any user in example.com, or any
 user in example.org or the particular users alice@bad.example.net,
 bob@good.example.net, and the user with the telephone number
 'tel:+1-212-555-1234'.  The last 'except' element is redundant since
 alice@example.com is already excluded through the first line.

Schulzrinne, et al. Standards Track [Page 13] RFC 4745 Common Policy February 2007

7.1.3.3. Matching Any Authenticated Identity within a Domain Except

        Enumerated Identities
 The <many> element with a 'domain' attribute and zero or more <except
 id="..."/> elements matches any authenticated user from the indicated
 domain except those explicitly enumerated.  The semantics of the 'id'
 attribute of the <except> element is described in Section 7.2.
 It is nonsensical to have domains in the 'id' attribute that do not
 match the value of the 'domain' attribute in the enclosing <many>
 element.
 An example is shown below:
 <?xml version="1.0" encoding="UTF-8"?>
 <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
     <rule id="f3g44r1">
         <conditions>
             <identity>
                 <many domain="example.com">
                     <except id="sip:alice@example.com"/>
                     <except id="sip:bob@example.com"/>
                 </many>
             </identity>
         </conditions>
         <actions/>
         <transformations/>
     </rule>
 </ruleset>
 This example matches any user within example.com (such as
 carol@example.com) except alice@example.com and bob@example.com.

7.2. Single Entity

 The 'id' attribute used in the <one> and in the <except> element
 refers to a single entity.  In the subsequent text, we use the term
 'single-user entity' as a placeholder for the <one> and the <except>
 element.  The <except> element fulfills the purpose of excluding
 elements from the solution set.
 A single-user entity matches the authenticated identity (as contained
 in the 'id' attribute) of exactly one entity or user.  If there is a
 match, the single-user entity is considered TRUE.  The single-user
 entity MUST NOT contain a 'domain' attribute.

Schulzrinne, et al. Standards Track [Page 14] RFC 4745 Common Policy February 2007

 The 'id' attribute contains an identity that MUST first be expressed
 as a URI.  Applications using this framework must describe how the
 identities they are using can be expressed as URIs.

7.3. Sphere

 The <sphere> element belongs to the group of condition elements.  It
 can be used to indicate a state (e.g., 'work', 'home', 'meeting',
 'travel') the PT is currently in.  A sphere condition matches only if
 the PT is currently in the state indicated.  The state may be
 conveyed by manual configuration or by some protocol.  For example,
 RPID [10] provides the ability to inform the PS of its current
 sphere.  The application domain needs to describe in more detail how
 the sphere state is determined.  Switching from one sphere to another
 causes a switch between different modes of visibility.  As a result,
 different subsets of rules might be applicable.
 The content of the 'value' attribute of the <sphere> element MAY
 contain more than one token.  The individual tokens MUST be separated
 by a blank character.  A logical OR is used for the matching the
 tokens against the sphere settings of the PT.  As an example, if the
 content of the 'value' attribute in the sphere attribute contains two
 tokens 'work' and 'home' then this part of the rule matches if the
 sphere for a particular PT is either 'work' OR 'home'.  To compare
 the content of the 'value' attribute in the <sphere> element with the
 stored state information about the PT's sphere setting a
 case-insensitive string comparison MUST be used for each individual
 token.  There is neither a registry for these values nor a language-
 specific indication of the sphere content.  As such, the tokens are
 treated as opaque strings.
 <?xml version="1.0" encoding="UTF-8"?>
 <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
   <rule id="f3g44r2">
     <conditions>
       <sphere value="work"/>
       <identity>
         <one id="sip:andrew@example.com"/>
       </identity>
     </conditions>
     <actions/>
     <transformations/>
   </rule>

Schulzrinne, et al. Standards Track [Page 15] RFC 4745 Common Policy February 2007

   <rule id="y6y55r2">
     <conditions>
       <sphere value="home"/>
       <identity>
         <one id="sip:allison@example.com"/>
       </identity>
     </conditions>
     <actions/>
     <transformations/>
   </rule>
   <rule id="z6y55r2">
     <conditions>
       <identity>
            <one id="sip:john@doe.example.com"/>
       </identity>
       <sphere value="home work"/>
     </conditions>
     <actions/>
     <transformations/>
   </rule>
 </ruleset>
 The rule example above illustrates that the rule with the entity
 andrew@example.com matches if the sphere is been set to 'work'.  In
 the second rule, the entity allison@example.com matches if the sphere
 is set to 'home'.  The third rule also matches since the value in the
 sphere element also contains the token 'home'.

7.4. Validity

 The <validity> element is the third condition element specified in
 this document.  It expresses the rule validity period by two
 attributes, a starting and an ending time.  The validity condition is
 TRUE if the current time is greater than or equal to at least one
 <from> child, but less than the <until> child after it.  This
 represents a logical OR operation across each <from> and <until>
 pair.  Times are expressed in XML dateTime format.  A rule maker
 might not always have access to the PS to invalidate some rules that
 grant permissions.  Hence, this mechanism allows invalidating granted
 permissions automatically without further interaction between the
 rule maker and the PS.  The PS does not remove the rules; instead the
 rule maker has to clean them up.

Schulzrinne, et al. Standards Track [Page 16] RFC 4745 Common Policy February 2007

 An example of a rule fragment is shown below:
 <?xml version="1.0" encoding="UTF-8"?>
 <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
   <rule id="f3g44r3">
     <conditions>
         <validity>
             <from>2003-08-15T10:20:00.000-05:00</from>
             <until>2003-09-15T10:20:00.000-05:00</until>
         </validity>
     </conditions>
     <actions/>
     <transformations/>
   </rule>
 </ruleset>
 The <validity> element MUST have the <from> and <until> subelements
 in pairs.  Multiple <from> and <until> elements might appear in pairs
 (i.e., without nesting of <from> and <until> elements).  Using
 multiple <validity> elements as subelements of the <conditions>
 element is not useful since all subelements of the <conditions>
 element are combined as a logical AND.

8. Actions

 While conditions are the 'if'-part of rules, actions and
 transformations form their 'then'-part.  The actions and
 transformations parts of a rule determine which operations the PS
 MUST execute after having received from a WR a data access request
 that matches all conditions of this rule.  Actions and
 transformations only permit certain operations; there is no 'deny'
 functionality.  Transformations exclusively specify PS-side
 operations that lead to a modification of the data items requested by
 the WR.  Regarding location data items, for instance, a
 transformation could force the PS to lower the precision of the
 location information that is returned to the WR.
 Actions, on the other hand, specify all remaining types of operations
 the PS is obliged to execute, i.e., all operations that are not of
 transformation type.  Actions are defined by application-specific
 usages of this framework.  The reader is referred to the
 corresponding extensions to see examples of such elements.

Schulzrinne, et al. Standards Track [Page 17] RFC 4745 Common Policy February 2007

9. Transformations

 Two sub-parts follow the conditions part of a rule: transformations
 and actions.  As defined in Section 8, transformations specify
 operations that the PS MUST execute and that modify the result that
 is returned to the WR.  This functionality is particularly helpful in
 reducing the granularity of information provided to the WR, as, for
 example, required for location privacy.  Transformations are defined
 by application-specific usages of this framework.
 A simple transformation example is provided in Section 10.

10. Procedure for Combining Permissions

10.1. Introduction

 This section describes how rules are selected and how actions and
 permissions are determined.  When a PS receives a request for access
 to privacy-sensitive data, the request is matched against the rule
 set.  A rule matches if all conditions contained as child elements in
 the <conditions> element of a rule evaluate to TRUE.  Each type of
 condition defines when it is TRUE.  All rules where the conditions
 match the request form the matching rule set.  The permissions in the
 matching rule set are combined using a set of combining rules (CRs)
 described in Section 10.2.

10.2. Combining Rules (CRs)

 Each type of permission is combined across all matching rules.  Each
 type of action or transformation is combined separately and
 independently.  The combining rules generate a combined permission.
 The combining rules depend only on the data type of permission.  If a
 particular permission type has no value in a rule, it assumes the
 lowest possible value for that permission for the purpose of
 computing the combined permission.  That value is given by the data
 type for booleans (FALSE) and sets (empty set), and MUST be defined
 by any extension to the Common Policy for other data types.
 For boolean permissions, the resulting permission is TRUE if and only
 if at least one permission in the matching rule set has a value of
 TRUE and FALSE otherwise.  For integer, real-valued and date-time
 permissions, the resulting permission is the maximum value across the
 permission values in the matching set of rules.  For sets, it is the
 union of values across the permissions in the matching rule set.

Schulzrinne, et al. Standards Track [Page 18] RFC 4745 Common Policy February 2007

10.3. Example

 In the following example we illustrate the process of combining
 permissions.  We will consider three conditions for our purpose,
 namely those of name identity (WR-ID), sphere, and validity
 (from,until).  The ID column is used as a rule identifier.  For
 editorial reasons we omit the domain part of the WR's identity.
 We use two actions in our example, namely X and Y.  The values of X
 and Y are of data types Boolean and Integer, respectively.
 The transformation, referred to as Z, uses values that can be set
 either to '+' (or 3), 'o' (or 2) or '-' (or 1).  Permission Z allows
 us to show the granularity reduction whereby a value of '+' shows the
 corresponding information unrestricted, and '-' shows nothing.  This
 permission might be related to location information or other presence
 attributes like mood.  Internally, we use the data type Integer for
 computing the permission of this attribute.
 The label 'NULL' in the table indicates that no value is available
 for a particular cell.
       Conditions                  Actions/Transformations
   +---------------------------------+---------------------+
   | Id  WR-ID    sphere  from until |  X       Y     Z    |
   +---------------------------------+---------------------+
   |  1   bob      home    A1    A2  |  TRUE    10    o    |
   |  2   alice    work    A1    A2  |  FALSE   5     +    |
   |  3   bob      work    A1    A2  |  TRUE    3     -    |
   |  4   tom      work    A1    A2  |  TRUE    5     +    |
   |  5   bob      work    A1    A3  |  NULL    12    o    |
   |  6   bob      work    B1    B2  |  FALSE   10    -    |
   +---------------------------------+---------------------+
 Again for editorial reasons, we use the following abbreviations for
 the two <validity> attributes 'from' and 'until':
   A1=2003-12-24T17:00:00+01:00
   A2=2003-12-24T21:00:00+01:00
   A3=2003-12-24T23:30:00+01:00
   B1=2003-12-22T17:00:00+01:00
   B2=2003-12-23T17:00:00+01:00
 Note that B1 < B2 < A1 < A2 < A3.
 The entity 'bob' acts as a WR and requests data items.  The rule set
 consists of the six rules shown in the table and identified by the
 values 1 to 6 in the 'Id' column.  The PS receives the query at

Schulzrinne, et al. Standards Track [Page 19] RFC 4745 Common Policy February 2007

 2003-12-24T17:15:00+01:00, which falls between A1 and A2.  In our
 example, we assume that the sphere value of the PT is currently set
 to 'work'.
 As a first step, it is necessary to determine which rules fire by
 evaluating the conditions part of each of them.
 Rule 1 does not match since the sphere condition does not match.
 Rule 2 does not match as the identity of the WR (here 'alice') does
 not equal 'bob'.  Rule 3 matches since all conditions evaluate to
 TRUE.  Rule 4 does not match as the identity of the WR (here 'tom')
 does not equal 'bob'.  Rule 5 matches.  Rule 6 does not match since
 the rule is not valid anymore.
 Only rules 3 and 5 fire.  We use the actions and transformations part
 of these two rules to determine the combined permission, as shown
 below.
           Actions/Transformations
   +-----+-----------------------+
   | Id  |  X       Y      Z     |
   +-----+-----------------------+
   |  3  |  TRUE     3     -     |
   |  5  |  NULL    12     o     |
   +-----+-----------------------+
 Each column is treated independently.  The combined value of X is set
 to TRUE since the NULL value equals FALSE according to the
 description in Section 10.2.  For the column with the name Y, we
 apply the maximum of 3 and 12, so that the combined value of Y is 12.
 For column Z, we again compute the maximum of 'o' and '-' (i.e., 2
 and 1) which is 'o' (2).
 The combined permission for all three columns is therefore:
           Actions/Transformations
         +-----------------------+
         |  X       Y      Z     |
         +-----------------------+
         |  TRUE    12     o     |
         +-----------------------+

Schulzrinne, et al. Standards Track [Page 20] RFC 4745 Common Policy February 2007

11. Meta Policies

 Meta policies authorize a rule maker to insert, update, or delete a
 particular rule or an entire rule set.  Some authorization policies
 are required to prevent unauthorized modification of rule sets.  Meta
 policies are outside the scope of this document.
 A simple implementation could restrict access to the rule set only to
 the PT but more sophisticated mechanisms could be useful.  As an
 example of such policies, one could think of parents configuring the
 policies for their children.

12. Example

 This section gives an example of an XML document valid with respect
 to the XML schema defined in Section 13.  Semantically richer
 examples can be found in documents that extend this schema with
 application-domain-specific data (e.g., location or presence
 information).
 Below a rule is shown with a condition that matches for a given
 authenticated identity (bob@example.com) and within a given time
 period.  Additionally, the rule matches only if the target has set
 its sphere to 'work'.
 <?xml version="1.0" encoding="UTF-8"?>
 <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
     <rule id="f3g44r1">
         <conditions>
             <identity>
                 <one id="sip:bob@example.com"/>
             </identity>
             <sphere value="work"/>
             <validity>
                 <from>2003-12-24T17:00:00+01:00</from>
                 <until>2003-12-24T19:00:00+01:00</until>
             </validity>
         </conditions>
         <actions/>
         <transformations/>
     </rule>
 </ruleset>

Schulzrinne, et al. Standards Track [Page 21] RFC 4745 Common Policy February 2007

13. XML Schema Definition

 This section provides the XML schema definition for the common policy
 markup language described in this document.

<?xml version="1.0" encoding="UTF-8"?> <xs:schema targetNamespace="urn:ietf:params:xml:ns:common-policy"

  xmlns:cp="urn:ietf:params:xml:ns:common-policy"
  xmlns:xs="http://www.w3.org/2001/XMLSchema"
  elementFormDefault="qualified" attributeFormDefault="unqualified">
  <!-- /ruleset -->
  <xs:element name="ruleset">
      <xs:complexType>
          <xs:complexContent>
              <xs:restriction base="xs:anyType">
                  <xs:sequence>
                      <xs:element name="rule" type="cp:ruleType"
                      minOccurs="0" maxOccurs="unbounded"/>
                  </xs:sequence>
              </xs:restriction>
          </xs:complexContent>
      </xs:complexType>
  </xs:element>
  <!-- /ruleset/rule -->
  <xs:complexType name="ruleType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:sequence>
                  <xs:element name="conditions"
                  type="cp:conditionsType" minOccurs="0"/>
                  <xs:element name="actions"
                  type="cp:extensibleType" minOccurs="0"/>
                  <xs:element name="transformations"
                  type="cp:extensibleType" minOccurs="0"/>
              </xs:sequence>
              <xs:attribute name="id" type="xs:ID" use="required"/>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>
  <!-- //rule/conditions -->
  <xs:complexType name="conditionsType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:choice maxOccurs="unbounded">
                  <xs:element name="identity"
                  type="cp:identityType" minOccurs="0"/>
                  <xs:element name="sphere"
                  type="cp:sphereType" minOccurs="0"/>

Schulzrinne, et al. Standards Track [Page 22] RFC 4745 Common Policy February 2007

                  <xs:element name="validity"
                  type="cp:validityType" minOccurs="0"/>
                  <xs:any namespace="##other" processContents="lax"
                  minOccurs="0" maxOccurs="unbounded"/>
              </xs:choice>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>
  <!-- //conditions/identity -->
  <xs:complexType name="identityType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:choice  minOccurs="1" maxOccurs="unbounded">
                  <xs:element name="one" type="cp:oneType"/>
                  <xs:element name="many" type="cp:manyType"/>
                  <xs:any namespace="##other" processContents="lax"/>
              </xs:choice>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>
  <!-- //identity/one -->
  <xs:complexType name="oneType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:sequence>
                  <xs:any namespace="##other"
                  minOccurs="0" processContents="lax"/>
              </xs:sequence>
              <xs:attribute name="id"
              type="xs:anyURI" use="required"/>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>
  <!-- //identity/many -->
  <xs:complexType name="manyType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:choice minOccurs="0" maxOccurs="unbounded">
                  <xs:element name="except" type="cp:exceptType"/>
                  <xs:any namespace="##other"
                  minOccurs="0" processContents="lax"/>
              </xs:choice>
              <xs:attribute name="domain"
              use="optional" type="xs:string"/>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>
  <!-- //many/except -->

Schulzrinne, et al. Standards Track [Page 23] RFC 4745 Common Policy February 2007

  <xs:complexType name="exceptType">
      <xs:attribute name="domain" type="xs:string" use="optional"/>
      <xs:attribute name="id" type="xs:anyURI" use="optional"/>
  </xs:complexType>
  <!-- //conditions/sphere -->
  <xs:complexType name="sphereType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:attribute name="value"
              type="xs:string" use="required"/>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>
  <!-- //conditions/validity -->
  <xs:complexType name="validityType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:sequence minOccurs="1" maxOccurs="unbounded">
                  <xs:element name="from" type="xs:dateTime"/>
                  <xs:element name="until" type="xs:dateTime"/>
              </xs:sequence>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>
  <!-- //rule/actions or //rule/transformations -->
  <xs:complexType name="extensibleType">
      <xs:complexContent>
          <xs:restriction base="xs:anyType">
              <xs:sequence>
                  <xs:any namespace="##other" processContents="lax"
                  minOccurs="0" maxOccurs="unbounded"/>
              </xs:sequence>
          </xs:restriction>
      </xs:complexContent>
  </xs:complexType>

</xs:schema>

Schulzrinne, et al. Standards Track [Page 24] RFC 4745 Common Policy February 2007

14. Security Considerations

 This document describes a framework for policies.  This framework is
 intended to be enhanced elsewhere by application-domain-specific
 data.  Security considerations are to a great extent application-data
 dependent, and therefore need to be covered by documents that extend
 the framework defined in this specification.  However, new action and
 transformation permissions along with their allowed values must be
 defined in a way so that the usage of the permissions combining rules
 of Section 10 does not lower the level of privacy protection.  See
 Section 10 for more details on this privacy issue.

15. IANA Considerations

 This section registers a new XML namespace, a new XML schema, and a
 new MIME type.  This section registers a new XML namespace per the
 procedures in [4].

15.1. Common Policy Namespace Registration

 URI:  urn:ietf:params:xml:ns:common-policy
 Registrant Contact:  IETF GEOPRIV working group, Henning Schulzrinne
    (hgs+geopriv@cs.columbia.edu).
 XML:
 BEGIN
 <?xml version="1.0"?>
 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
   "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
 <html xmlns="http://www.w3.org/1999/xhtml">
 <head>
   <meta http-equiv="content-type"
         content="text/html;charset=iso-8859-1"/>
   <title>Common Policy Namespace</title>
 </head>
 <body>
   <h1>Namespace for Common Authorization Policies</h1>
   <h2>urn:ietf:params:xml:ns:common-policy</h2>
 <p>See <a href="ftp://ftp.rfc-editor.org/in-notes/rfc4745.txt">
    RFC 4745</a>.</p>
 </body>
 </html>
 END

Schulzrinne, et al. Standards Track [Page 25] RFC 4745 Common Policy February 2007

15.2. Content-type Registration for 'application/auth-policy+xml'

 This specification requests the registration of a new MIME type
 according to the procedures of RFC 4288 [5] and guidelines in RFC
 3023 [6].
 MIME media type name:  application
 MIME subtype name:  auth-policy+xml
 Mandatory parameters:  none
 Optional parameters:  charset
    Indicates the character encoding of enclosed XML.
 Encoding considerations:
    Uses XML, which can employ 8-bit characters, depending on the
    character encoding used.  See RFC 3023 [6], Section 3.2.
 Security considerations:
    This content type is designed to carry authorization policies.
    Appropriate precautions should be adopted to limit disclosure of
    this information.  Please refer to Section 14 of RFC 4745 and to
    the security considerations described in Section 10 of RFC 3023
    [6] for more information.
 Interoperability considerations:  None
 Published specification:  RFC 4745
 Applications which use this media type:
    Presence- and location-based systems
 Additional information:
    Magic Number:  None
    File Extension:  .apxml
    Macintosh file type code:  'TEXT'
 Personal and email address for further information:
    Hannes Tschofenig, Hannes.Tschofenig@siemens.com

Schulzrinne, et al. Standards Track [Page 26] RFC 4745 Common Policy February 2007

 Intended usage:  LIMITED USE
 Author:
    This specification is a work item of the IETF GEOPRIV working
    group, with mailing list address <geopriv@ietf.org>.
 Change controller:
    The IESG <iesg@ietf.org>

15.3. Common Policy Schema Registration

 URI:  urn:ietf:params:xml:schema:common-policy
 Registrant Contact:  IETF GEOPRIV working group, Henning Schulzrinne
    (hgs+geopriv@cs.columbia.edu).
 XML:  The XML schema to be registered is contained in Section 13.
    Its first line is
 <?xml version="1.0" encoding="UTF-8"?>
 and its last line is
 </xs:schema>

16. References

16.1. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  Duerst, M. and M. Suignard, "Internationalized Resource
      Identifiers (IRIs)", RFC 3987, January 2005.
 [3]  Faltstrom, P., Hoffman, P., and A. Costello, "Internationalizing
      Domain Names in Applications (IDNA)", RFC 3490, March 2003.
 [4]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
      January 2004.
 [5]  Freed, N. and J. Klensin, "Media Type Specifications and
      Registration Procedures", BCP 13, RFC 4288, December 2005.
 [6]  Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
      RFC 3023, January 2001.

Schulzrinne, et al. Standards Track [Page 27] RFC 4745 Common Policy February 2007

16.2. Informative References

 [7]  Rosenberg, J., "Presence Authorization Rules", Work in Progress,
      June 2006.
 [8]  Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J., and J.
      Polk, "A Document Format for Expressing Privacy Preferences for
      Location Information", Work in Progress, February 2006.
 [9]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
      Polk, "Geopriv Requirements", RFC 3693, February 2004.
 [10] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. Rosenberg,
      "RPID: Rich Presence Extensions to the Presence Information Data
      Format (PIDF)", RFC 4480, July 2006.

Schulzrinne, et al. Standards Track [Page 28] RFC 4745 Common Policy February 2007

Appendix A. Contributors

 We would like to thank Christian Guenther for his help with initial
 versions of this document.

Appendix B. Acknowledgments

 This document is partially based on the discussions within the IETF
 GEOPRIV working group.  Discussions at the Geopriv Interim Meeting
 2003 in Washington, D.C., helped the working group to make progress
 on the authorization policies based on the discussions among the
 participants.
 We particularly want to thank Allison Mankin <mankin@psg.com>,
 Randall Gellens <rg+ietf@qualcomm.com>, Andrew Newton
 <anewton@ecotroph.net>, Ted Hardie <hardie@qualcomm.com>, and Jon
 Peterson <jon.peterson@neustar.biz> for discussing a number of
 details with us.  They helped us to improve the quality of this
 document.  Allison, Ted, and Andrew also helped us to make good
 progress with the internationalization support of the identifier/
 domain attributes.
 Furthermore, we would like to thank the IETF SIMPLE working group for
 their discussions of J. Rosenberg's draft on presence authorization
 policies.  We would also like to thank Stefan Berg, Murugaraj
 Shanmugam, Christian Schmidt, Martin Thomson, Markus Isomaki, Aki
 Niemi, Eva Maria Leppanen, Josip Matanovic, and Mark Baker for their
 comments.  Martin Thomson helped us with the XML schema.  Mark Baker
 provided a review of the media type.  Scott Brim provided a review on
 behalf of the General Area Review Team.

Schulzrinne, et al. Standards Track [Page 29] RFC 4745 Common Policy February 2007

Authors' Addresses

 Henning Schulzrinne
 Columbia University
 Department of Computer Science
 450 Computer Science Building
 New York, NY  10027
 USA
 Phone: +1 212 939 7042
 EMail: schulzrinne@cs.columbia.edu
 URI:   http://www.cs.columbia.edu/~hgs
 Hannes Tschofenig
 Siemens Networks GmbH & Co KG
 Otto-Hahn-Ring 6
 Munich, Bavaria  81739
 Germany
 EMail: Hannes.Tschofenig@siemens.com
 URI:   http://www.tschofenig.com
 John B. Morris, Jr.
 Center for Democracy and Technology
 1634 I Street NW, Suite 1100
 Washington, DC  20006
 USA
 EMail: jmorris@cdt.org
 URI:   http://www.cdt.org
 Jorge R. Cuellar
 Siemens
 Otto-Hahn-Ring 6
 Munich, Bavaria  81739
 Germany
 EMail: Jorge.Cuellar@siemens.com

Schulzrinne, et al. Standards Track [Page 30] RFC 4745 Common Policy February 2007

 James Polk
 Cisco
 2200 East President George Bush Turnpike
 Richardson, Texas  75082
 USA
 EMail: jmpolk@cisco.com
 Jonathan Rosenberg
 Cisco Systems
 600 Lanidex Plaza
 Parsippany, New York  07054
 USA
 EMail: jdrosen@cisco.com
 URI:   http://www.jdrosen.net

Schulzrinne, et al. Standards Track [Page 31] RFC 4745 Common Policy February 2007

Full Copyright Statement

 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.

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
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 attempt made to obtain a general license or permission for the use of
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 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.

Schulzrinne, et al. Standards Track [Page 32]

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