SIPPING Working Group                                            V. Hilt
Internet-Draft                             Bell Labs/Lucent Technologies
Expires: August 10, 2005                                    G. Camarillo
                                                                Ericsson
                                                            J. Rosenberg
                                                           Cisco Systems
                                                        February 9, 2005

 Session Initiation  Protocol (SIP) Session Policies - Document Format
               and Session-Independent Delivery Mechanism
               draft-ietf-sipping-session-indep-policy-02

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This draft defines a delivery mechanism for SIP session policies that
   is independent of a specific SIP session.  It also defines the Basic
   Session Policy Format (BSPF), which is a minimal, XML-based format


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   for session policies.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.   Session-Independent Policy Mechanism . . . . . . . . . . . .   4
     3.1  Subscriber Behavior  . . . . . . . . . . . . . . . . . . .   4
     3.2  Notifier Behavior  . . . . . . . . . . . . . . . . . . . .   6
   4.   Policy Format Design . . . . . . . . . . . . . . . . . . . .   6
     4.1  Policy Model . . . . . . . . . . . . . . . . . . . . . . .   6
     4.2  Unidirectional Policies  . . . . . . . . . . . . . . . . .   7
     4.3  Per-Stream Policies  . . . . . . . . . . . . . . . . . . .   7
     4.4  Merging Policies . . . . . . . . . . . . . . . . . . . . .   7
   5.   Basic Session Policy Format  . . . . . . . . . . . . . . . .   8
     5.1  MIME Type and Namespace  . . . . . . . . . . . . . . . . .   8
     5.2  Extensibility  . . . . . . . . . . . . . . . . . . . . . .   9
     5.3  XML Format Definition  . . . . . . . . . . . . . . . . . .   9
       5.3.1  The <session-policy> Element . . . . . . . . . . . . .   9
       5.3.2  The <context> Element  . . . . . . . . . . . . . . . .   9
       5.3.3  The <domain> Element . . . . . . . . . . . . . . . . .  10
       5.3.4  The <contact> Element  . . . . . . . . . . . . . . . .  10
       5.3.5  The <info> Element . . . . . . . . . . . . . . . . . .  10
       5.3.6  The <entity> Element . . . . . . . . . . . . . . . . .  10
       5.3.7  The <media-types> Element  . . . . . . . . . . . . . .  10
       5.3.8  The <media-type> Element . . . . . . . . . . . . . . .  11
       5.3.9  The <codecs> Element . . . . . . . . . . . . . . . . .  11
       5.3.10   The <codec> Element  . . . . . . . . . . . . . . . .  12
       5.3.11   The <media-intermediary> Element . . . . . . . . . .  12
       5.3.12   The <int-uri> Element  . . . . . . . . . . . . . . .  13
       5.3.13   The <int-lroute> Element . . . . . . . . . . . . . .  13
       5.3.14   The <max-bandwidth> Element  . . . . . . . . . . . .  13
       5.3.15   The <qos> Element  . . . . . . . . . . . . . . . . .  14
       5.3.16   Open Issue: Other Elements . . . . . . . . . . . . .  14
     5.4  Example  . . . . . . . . . . . . . . . . . . . . . . . . .  14
     5.5  Schema Definition  . . . . . . . . . . . . . . . . . . . .  15
   6.   Security Considerations  . . . . . . . . . . . . . . . . . .  18
   7.   IANA Considerations  . . . . . . . . . . . . . . . . . . . .  18
     7.1  MIME Registration for application/session-policy+xml . . .  18
     7.2  URN Sub-Namespace Registration for
          urn:ietf:params:xml:ns:sessionpolicy . . . . . . . . . . .  19
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  21
   8.   References . . . . . . . . . . . . . . . . . . . . . . . . .  20
   A.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . .  21
        Intellectual Property and Copyright Statements . . . . . . .  23



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1.  Introduction

   Some domains have policies in place, which impact the sessions
   established using the Session Initiation Protocol (SIP) [15].  These
   policies are often needed to support the network infrastructure or
   for the execution of services.  For example, wireless networks
   usually have limited resources for media traffic.  A wireless network
   provider may want to restrict codec usage on the network to lower
   rate codecs or disallow the use of high bandwidth media types such as
   video.

   In another example, a network has a resource reservation
   infrastructure in place, which enables user agents to request Quality
   of Service (QoS) for media streams.  With session policies, the
   network can tell user agents that a QoS infrastructure is present and
   ask user agents to use specific parameters or provide certain
   credentials when requesting QoS.

   In a third example, a user has subscribed to a service that requires
   the media streams to be routed through a media intermediary.  The
   service provider would like to tell the user agent to direct the
   media streams to this intermediary and to use a certain source
   routing scheme (e.g.  IP-in-IP tunneling).  Knowing this policy
   enables the user to use this service in any network from which the
   intermediary can be reached.

   Domains sometimes enforce policies they have in place.  For example,
   a domain might have a configuration in which all packets containing a
   certain audio codec are dropped.  Unfortunately, enforcement
   mechanisms usually do not inform the user about the policies they are
   enforcing and silently keep the user from doing anything against
   them.  This may lead to the malfunctioning of devices that is
   incomprehensible to the user.  With session policies, the user knows
   about the restricted codecs and can use a different codec or simply
   connect to a domain with less stringent policies.  Session policies
   provide an important combination of consent coupled with enforcement.
   That is, the user becomes aware of the policy and needs to act on it,
   but the provider still retains the right to enforce the policy.

   Session-policies can be set up in two different ways: specifically
   for a session or independent of a session.  Session-specific policies
   are created for one particular session, usually under consideration
   of certain aspects of this session (e.g.  the IP addresses and ports
   that are used for media).  Since session-specific policies are
   tailored to a session, they only apply to the session they are
   created for.  These policies require a delivery mechanism that
   enables the exchange of session policy information at the time a
   session is established.  The framework for session-specific policies


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   [3] defines such a delivery mechanism for session-specific policies.

   Session-independent policies on the other hand are independent of a
   specific session and generally apply to the sessions set up by a user
   agent.  An example is a policy which prohibits the use of
   high-bandwidth codecs.  In principle, these policies could also be
   delivered to user agents individually for each session, using the
   session-specific policy framework.  However, since these policies
   apply to many sessions, it is more efficient to deliver them to user
   agents only when the user agent is initialized or a policy changes.
   This draft defines a delivery mechanism for session-independent
   policies.

   This draft also defines the Basic Session Policy Format (BSPF).  BSPF
   is a minimal session policy format aimed at achieving
   interoperability between different user agents and policy servers.
   This format introduces a common data model and defines a basic set of
   policy elements.  The format is based on XML [16] and can be extended
   using XML extension mechanisms.  The document format is independent
   of the policy delivery mechanism and can be used for
   session-independent and session-specific session policies.

2.  Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described in BCP 14, [1] and indicate requirement levels for
   compliant implementations.

3.  Session-Independent Policy Mechanism

   Session-independent policies can be delivered to UAs using the
   mechanism defined in the Framework for SIP User  Agent Profile
   Delivery [12].  Session-independent policies can reside on the same
   server as other configuration information and they can be delivered
   to UAs in conjunction with this information.  Session-independent
   policies can also reside on a separate policy server, which is
   independent of a configuration server.  A UA may receive
   session-independent policies from multiple policy servers.  The
   following sections describe the subscription to the
   session-independent policies relevant for a UA.

3.1  Subscriber Behavior

   A UA can express interest in session-independent policies by
   subscribing to session policies using the mechanism defined in [12].
   If the UA has already received the URIs of all relevant session


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   policy servers (e.g., through configuration) it SHOULD use these URIs
   to subscribe to session-independent policies.

   Session-independent policies are frequently provided to a UA by the
   following two network domains: the domain a user registers at (i.e.,
   the domain in the address-of-record (AoR)) and the domain the UA is
   physically connected to.  A policy server in the AoR-domain may, for
   example, provide policies needed for services the user has subscribed
   to.  The domain that provides the physical network connection may
   have policies needed to ensure the operativeness of the network,
   e.g., by limiting the bandwidth available to a UA.  A UA SHOULD
   attempt to subscribe to the policy servers in both domains.  These
   subscriptions are established using the "user" (for subscriptions to
   the AoR-domains) and the "local" (for subscriptions to the network
   domain) profile-types [12].  A UA SHOULD modify these subscriptions
   as described below in following events:

   o  The UA changes the registration status of one of its AoR.  This
      occurs, for example, when a UA starts up and registers its AoRs,
      when it shuts down and deregisters AoRs, or when a new AoR is
      added to a UA.  In these events, the UA SHOULD establish
      subscriptions for each new AoR using the "user" and the "local"
      profile-types.  It SHOULD terminate the subscriptions for all AoRs
      that have been removed.
   o  The domain the UA is connected to changes.  The UA SHOULD create a
      new subscription for each AoR using the "local" profile-type.  It
      SHOULD terminate all existing subscriptions for the "local"
      profile-type.  It does not need to change the subscriptions for
      "user" profiles.

   If a subscriber is unable to successfully establish a subscription,
   it SHOULD NOT attempt to re-try this subscription, unless one of the
   above events occurs again.  This is to limit the number of SUBSCRIBE
   requests sent within domains that do not support session-policies.

   A subscriber compliant to this specification MUST indicate its
   support for session-independent session policies by adding the MIME
   types of supported session policy formats to the Accept header of the
   SUBSCRIBE request.  This specification defines the new MIME type
   "application/session-policy+xml", which MUST be supported by UAs
   compliant to this specification.  UAs MAY also indicate support for
   MIME type extensions (e.g.  an additional XML namespace) using [4].

   A subscriber may receive a 406 in response to a SUBSCRIBE request.
   This indicates that the notifier requires the support of a session
   policy format that was not in the Accept header of the SUBSCRIBE
   request.  This means that the notifier has session policies that are
   required in the network but not supported by the subscriber.  As a


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   consequence, the subscriber may experience difficulties when setting
   up a session without these policies.

3.2  Notifier Behavior

   A network may have session policies in place that must be supported
   by a UA.  If the notifier receives a SUBSCRIBE request, which does
   not list all MIME types and MIME type extensions in the Accept header
   that are needed for policies, it MUST reject the request with a 406
   response.  A policy format is needed, if the network has policies in
   this format that must be used by the UA.  The notifier SHOULD NOT
   return a 406 if an unsupported format contains optional policies.

4.  Policy Format Design

   The following sections describe design considerations for an
   XML-based model for session policies.

4.1  Policy Model

   Session policies influence aspects of a SIP session by defining
   constraints.  A constraint impacts a specific aspect of a SIP session
   (e.g.  the codecs that can be used in this session).  Policy
   constraints are modeled as XML elements.  Each policy element
   expresses a certain constraint.  Policy elements can contain a simple
   value or act as a container, which holds multiple alternative values
   for this policy.

   Elements that express policies have a 'policy' attribute.  This
   attribute defines the constraining properties of the XML element.
   The following values are defined for the 'policy' attribute:

   o  mandatory: the value contained in the element is mandatory and
      MUST be used in sessions.  This is the default value that is used
      if the 'policy' attribute is omitted.
   o  allow: the value contained in the element is allowed and MAY be
      used in sessions.
   o  disallow: the value contained in the element is forbidden and MUST
      NOT be used in sessions.

   Polices consisting of one single value can be expressed by a simple
   policy element.  The following is an example of a policy defining an
   upper limit for media bandwidth:

   <max-bandwidth>80</max-bandwidth>

   Policies consisting of multiple values can be expressed using a


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   container element.  The container contains multiple elements, which
   define possible values.  The policy attribute of the container
   specifies the policy that applies to all values not listed in the
   container.  The policy attribute of each element in the container
   defines the policy for that item.  The following example shows a
   policy that requires the media type audio and allows video in
   sessions:

   <media-types policy="disallow">
     <media-type policy="mandatory">audio</media-type>
     <media-type policy="allow">video</media-type>
   </media-types>

4.2  Unidirectional Policies

   Some policies only affect media streams flowing into one direction,
   e.g., only outgoing streams.  Unidirectional policies can be
   expressed by adding a 'direction' attribute to the respective policy
   element.

   The 'direction' attribute can have the following values:

   o  recvonly: the policy only applies to incoming streams.
   o  sendonly: the policy only applies to outgoing streams.
   o  sendrecv: the policy applies to streams in both directions.  This
      is the default value that is used if the 'direction' attribute is
      omitted.

4.3  Per-Stream Policies

   Policies can be specific to a certain media stream.  The stream to
   which a policy applies to must be identifiable through a label [7].
   Per-stream policies can be expressed by adding a 'label' attribute to
   the respective policy element.  Such a policy only applies to the
   identified stream.  If the label value is unknown to the recipient,
   the policy must be ignored.

   Per-stream policies require that the policy server has access to the
   session description in order to extract the stream label.  For this
   reason, per-stream policies are typically used in session-specific
   policies.

4.4  Merging Policies

   A UA may receive policy documents from multiple sources, which need
   to be merged into a single combined policy document the UA can work


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   with.

   Policies that define a single value (e.g.  maximum bandwidth) require
   the selection of one value during the merging process.  The selection
   criteria must be defined individually for each element (e.g.  select
   lowest value) in the schema definition.

   Policies that allow multiple values can be merged by combining all
   values and adjusting the 'policy' attribute for values that exist in
   both documents.  Table 1 provides a matrix for merging the 'policy'
   attributes.  Additional merging rules may be required for some
   elements.  They must be specified in the schema definition.

   Some constellations are not feasible and constitute a policy conflict
   that can not be resolved automatically.  If the conflicting policies
   are enforced by the network, the UA may experience difficulties when
   setting up a session.

   pol 1 \ pol 2 | mandatory |   allow   | disallow
   --------------+-----------+-----------+-----------
   mandatory     | mandatory | mandatory | conflict!
   allow         | mandatory |   allow   | disallow
   disallow      | conflict! | disallow  | disallow

               Table 1: merging policies.

   The combined policy MUST again be valid and well-formed according to
   policy schema definitions.  A policy conflict occurs if the combined
   policy is not a well-formed document after the merging process is
   completed.

5.  Basic Session Policy Format

   The Basic Session Policy Format (BSPF) defines the structure of and a
   root element for session policy documents.  It provides a minimal set
   of policy elements as required by [14].  To enable interoperability
   between UAs and policy servers, this format MUST be supported by all
   UAs compliant to this specification.

      Note: It is the goal to keep this specification aligned with the
      schema for user agent profile data sets [13] to simplify the
      processing of policy and configuration data.

5.1  MIME Type and Namespace

   The MIME type for the Basic Session Policy Format is:


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      application/session-policy+xml

   This specification makes use of XML namespaces [5].  The namespace
   URIs for schemas defined in this specification are URNs [8], using
   the namespace identifier 'ietf' defined by [9] and extended by [6].
   The namespace URN for the BSPF schema is:

      urn:ietf:params:xml:ns:sessionpolicy

5.2  Extensibility

   The BSPF format can be extended using XML extension mechanisms.  In
   particular, elements from different XML namespaces MAY be present
   within a BSPF document for the purposes of extensibility; elements or
   attributes from unknown namespaces MUST be ignored.

5.3  XML Format Definition

   A BSPF document is an XML [16] document that MUST be well-formed and
   MUST be valid according to schemas, including extension schemas,
   available to the validator and applicable to the XML document.  BSPF
   documents MUST be based on XML 1.0 and MUST be encoded using UTF-8.

5.3.1  The <session-policy> Element

   The root element of a BSPF document is the <session-policy> element.

   The <session-policy> element MAY contain an optional <context>
   element and multiple (including zero) <media-types>, <codecs>,
   <media-intermediary>, <qos>, and <max-bandwidth> elements as well as
   elements from other namespaces.

5.3.2  The <context> Element

   The <context> element provides context information about this policy.

   The <context> element is optional in a <session-policy> element.  It
   MAY contain a <domain>, multiple <contact>, a <info>, and multiple
   <entity> elements.

      Merging policies: the <context> element is not subject to merging.
      Information in the context element may be used to assist the user
      if a policy conflict occurs.  Policies that affect different
      entities (e.g.  different AoRs) on a user agent and therefore have
      different <entity> values do not need to be merged.  A policy
      affecting all entities on a user agent (i.e.  no <entity> element
      is specified) must be merged with the policy for a specific
      entity.


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5.3.3  The <domain> Element

   The <domain> element contains a URI that identifies the domain which
   has issued this policy.

   The <domain> element is optional and MAY occur only once inside a
   <context> element.

5.3.4  The <contact> Element

   The <contact> element contains a contact address (e.g.  a SIP URI or
   email address) under which the issuer of this policy can be reached.

   The <contact> element is optional and MAY occur multiple times inside
   a <context> element.

5.3.5  The <info> Element

   The <info> element provides a short textual description of the policy
   that should be intelligible to the human user.

   The <info> element is optional and MAY occur only once inside a
   <context> element.

5.3.6  The <entity> Element

   The <entity> element contains a URI that identifies the user or
   device whose policy information is reported in this policy instance.
   The policy only applies to the sessions that involve this entity.  If
   this element is not present, the policy applies to all entities on a
   UA.

   The <entity> element is optional and MAY occur multiple times inside
   a <context> element.

5.3.7  The <media-types> Element

   The <media-types> element expresses a policy for the use of media
   types (e.g.  audio, video).  A policy defines the media types that
   must be used, may be used, or must not be used in a session.

   This element has an mandatory 'policy' attribute as defined in
   Section 4.1.  The 'policy' attribute specifies the default policy for
   all media types that are not listed inside this element.

   This element has an optional 'direction' attribute as defined in
   Section 4.2.


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   The <media-types> element is optional in a <session-policy> element
   and MAY occur multiple times.  It MUST contain one or more
   <media-type> elements.

      Merging policies: the 'policy' attribute of the <media-types>
      element and <media-type> elements with the same value is adjusted
      according to Table 1.

5.3.8  The <media-type> Element

   The <media-type> element defines a policy for the use of the media
   type identified by this elements value.  This value MUST be the name
   of a IANA registered media type (see [2]), such as 'audio', 'video',
   'text', or 'application'.

   This element has a mandatory 'policy' attribute as defined in Section
   4.1.

   The <media-type> element is mandatory and MAY occur multiple times
   inside a <media-types> element.

5.3.9  The <codecs> Element

   The <codecs> element expresses a policy for the use of codecs.  A
   policy can define that a codec must be used, may be used, or must not
   be used in a session.  A policy MUST allow the use of at least one
   codec and MUST NOT define more than one mandatory codec for a media
   type.

   This element has a mandatory 'policy' attribute as defined in Section
   4.1.  The 'policy' attribute specifies the default policy for all
   codecs that are not listed inside this element.

   This element has an optional 'direction' attribute as defined in
   Section 4.2.

   This element has an optional 'label' attribute as defined in Section
   4.3.

   The <codecs> element is optional in a <session-policy> element and
   MAY occur multiple times.  It MUST contain one or more <codec>
   elements.

      Merging policies: the 'policy' attribute of the <codecs> element
      and <codec> elements with the same value is adjusted according to
      Table 1.



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5.3.10  The <codec> Element

   The <codec> element defines a policy for the use of the codec
   identified by this elements value.  This value MUST be the name of a
   registered MIME type for a encoding (see [2]), such as "PCMA",
   "G729", or "H263".

   This element has a mandatory 'policy' attribute as defined in Section
   4.1.

   The <codec> element is mandatory and MAY occur multiple times inside
   a <codecs> element.

5.3.11  The <media-intermediary> Element

   The <media-intermediary> element expresses a policy for routing a
   media stream through a media intermediary.  The purpose of the
   <media-intermediary> element is to tell the UA to send the media for
   a particular stream through an IP address and port of an
   intermediary.  Instead of merely sending the media there, the UA can
   instead specify a source route, which touches that intermediary, but
   also any other intermediaries and then the final recipient.  Thus, if
   there are N hops, including the final recipient, there needs to be a
   way for the media stream to specify N destinations.  The way these N
   destinations should be identified when sending the media stream is
   expressed using the <int-lroute> element.

   This element has a mandatory 'policy' attribute as defined in Section
   4.1).  This attribute defines whether routing media streams through
   this intermediary is mandatory or allowed.

   This element has an optional 'label' attribute as defined in Section
   4.3.

   The <media-intermediary> element is optional in a <session-policy>
   element and MAY occur multiple times.  The order of
   <media-intermediary> element instances is significant.  It defines
   the order in which the media intermediaries must be traversed.  The
   UA sends the media stream to the intermediary listed first, then to
   the intermediary listed next and so on.  The <media-intermediary>
   element MUST contain one <int-uri> and one <int-lroute> element.

      Merging policies: the intermediaries defined in all policies are
      traversed.  For session-independent policies, intermediaries
      received through a subscription using the "local" profile-type are
      traversed before those received through a "user" profile-type
      subscription.  For session-specific policies, intermediaries are
      traversed in the order in which policy URIs are received (i.e.


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      local intermediaries first).

5.3.12  The <int-uri> Element

   The <int-uri> element contains a URI that identifies the IP address
   and port number of a media intermediary.  The UA uses this URI to
   send its media streams to the intermediary.  If a protocol uses
   multiple subsequent ports (e.g.  RTP) only the lowest port number
   needs to be identified.

   The <int-uri> element occurs exactly once inside a
   <media-intermediary> element.

5.3.13  The <int-lroute> Element

   The <int-lroute> element identifies the loose source routing protocol
   to be used with this intermediary.  The value of this element can be
   one of the following:

   o  ip-in-ip: IP-in-IP tunneling  is used to specify the hops of media
      traversal.  The ultimate destination is specified in the
      destination IP of the innermost packet.  Each subsequent hop
      results in another encapsulation, with the destination of that hop
      in the destination IP address of the packet.
   o  ip-loose: IP provides a loose routing mechanism that allows the
      sender of an IP datagram to specify a set of IP addresses that are
      to be visited on the way before reaching the final destination.
   o  media-specific: media protocols can provide their own loose
      routing mechanism.  If that is the case, the loose routing
      mechanism of that protocol is used.  As an example, SIP provides
      its own loose routing mechanisms with the Route header.  It can be
      used to direct an instant message using the SIP MESSAGE method
      through a set of intermediaries.
   o  none: if there is no loose-routing mechanism available, the media
      is just sent to the first media intermediary listed in the header.
      Note that this requires the intermediary to know where to forward
      the packets to.  Such a route must be set up in the intermediary
      through other means.  For example, with session-specific policies,
      the policy server can extract the destination address from the
      session description.

   The <int-lroute> element occurs exactly once inside a
   <media-intermediary> element.

5.3.14  The <max-bandwidth> Element

   The <max-bandwidth> element contains the maximum bandwidth in
   kilobits per second an entity can use for its media streams.


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   This element has an optional 'direction' attribute as defined in
   Section 4.2.  If the direction attribute is present, the
   <max-bandwidth> element contains the bandwidth available in the
   identified direction.

   The <max-bandwidth> element is optional in a <session-policy> element
   and MAY occur only once.

      Merging policies: the lowest max-bandwidth value is used.

      Open issue: The maximum bandwidth policy is not part of the policy
      requirements.  Should it be part of BSPF?

5.3.15  The <qos> Element

      Open issue: what needs to go in here?

5.3.16  Open Issue: Other Elements

   A number of additional elements have been proposed for a policy
   language:

   o  maximum number of streams
   o  maximum number of sessions
   o  maximum number of streams per session
   o  maximum bandwidth per session
   o  maximum bandwidth per stream
   o  external address and port
   o  media transport protocol
   o  outbound proxy
   o  SIP methods
   o  SIP option tags
   o  SIP transport protocol
   o  body disposition
   o  body format
   o  body encryption

   Is it desirable to add any of these to the BSPF format? Some of these
   items could become part of an extension to BSPF.

5.4  Example

   The following example describes a policy that requires the use of
   audio, allows the use of video and prohibits the use of other media
   types.  It allows the use of any codec except G.723 and G.729.  The
   policy also inserts a media intermediary into outgoing media streams.



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   <session-policy>
     <context>
       <domain>example.com</domain>
       <contact>sip:policy_manager@example.com</contact>
       <info>Access network policies</info>
     </context>
     <media-types policy="disallow">
       <media-type policy="mandatory">audio</media-type>
       <media-type policy="allow">video</media-type>
     </media-types>
     <codecs policy="allow">
       <codec policy="disallow">G729</codec>
       <codec policy="disallow">G723</codec>
     </codecs>
     <media-intermediary direction="sendonly" policy="mandatory">
       <int-uri>123.234.123.234:6000</int-uri>
       <int-lroute>ip-in-ip</int-lroute>
     </media-intermediary>
   </session-policy>

5.5  Schema Definition

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema targetNamespace="urn:ietf:params:xml:ns:sessionpolicy"
         xmlns:tns="urn:ietf:params:xml:ns:sessionpolicy"
         xmlns:xs="http://www.w3.org/2001/XMLSchema"
         elementFormDefault="qualified"
         attributeFormDefault="unqualified">

     <xs:element name="session-policy" type="tns:session-policy"/>

     <xs:complexType name="session-policy">
       <xs:sequence>
         <xs:element name="context" type="tns:context" minOccurs="0"
           maxOccurs="1"/>
         <xs:element name="media-types" type="tns:media-types"
           minOccurs="0" maxOccurs="unbounded"/>
         <xs:element name="codecs" type="tns:codecs" minOccurs="0"
           maxOccurs="unbounded"/>
         <xs:element name="media-intermediary"
           type="tns:media-intermediary" minOccurs="0"
           maxOccurs="unbounded"/>
         <xs:element name="max-bandwidth" type="tns:max-bandwidth"
           minOccurs="0" maxOccurs="unbounded"/>
       </xs:sequence>


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     </xs:complexType>

     <xs:complexType name="context">
       <xs:sequence>
         <xs:element name="domain" type="xs:anyURI" minOccurs="0"
           maxOccurs="1"/>
         <xs:element name="contact" type="xs:anyURI" minOccurs="0"
           maxOccurs="unbounded"/>
         <xs:element name="info" type="xs:string"
            minOccurs="0" maxOccurs="1"/>
         <xs:element name="entity" type="xs:anyURI" minOccurs="0"
           maxOccurs="unbounded"/>
       </xs:sequence>
     </xs:complexType>

     <xs:complexType name="media-types">
       <xs:sequence>
         <xs:element name="media-type" type="tns:media-type" minOccurs="1"
           maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="policy" type="tns:policyValue"
         use="required"/>
       <xs:attribute name="direction" type="tns:directionValue"
         use="optional" default="sendrecv"/>
     </xs:complexType>

     <xs:complexType name="codecs">
       <xs:sequence>
         <xs:element name="codec" type="tns:codec" minOccurs="1"
           maxOccurs="unbounded"/>
       </xs:sequence>
       <xs:attribute name="policy" type="tns:policyValue"
         use="required"/>
       <xs:attribute name="direction" type="tns:directionValue"
         use="optional" default="sendrecv"/>
       <xs:attribute name="label" type="xs:string" use="optional"/>
     </xs:complexType>

     <xs:complexType name="media-intermediary">
       <xs:sequence>
         <xs:element name="int-uri" type="xs:anyURI" minOccurs="1"
           maxOccurs="1"/>
         <xs:element name="int-lroute" type="tns:int-lroute" minOccurs="1"
           maxOccurs="1"/>
       </xs:sequence>
       <xs:attribute name="policy" type="tns:policyValue"
         use="required"/>


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       <xs:attribute name="label" type="xs:string" use="optional"/>
     </xs:complexType>

     <xs:complexType name="max-bandwidth">
       <xs:simpleContent>
         <xs:extension base="xs:positiveInteger">
           <xs:attribute name="policy" type="tns:policyValue"
             use="required"/>
         </xs:extension>
       </xs:simpleContent>
     </xs:complexType>

     <xs:complexType name="media-type">
       <xs:simpleContent>
         <xs:extension base="xs:string">
           <xs:attribute name="policy" type="tns:policyValue"
             use="required"/>
         </xs:extension>
       </xs:simpleContent>
     </xs:complexType>

     <xs:complexType name="codec">
       <xs:simpleContent>
         <xs:extension base="xs:string">
           <xs:attribute name="policy" type="tns:policyValue"
             use="required"/>
         </xs:extension>
       </xs:simpleContent>
     </xs:complexType>

     <xs:simpleType name="int-lroute">
       <xs:restriction base="xs:string">
         <xs:enumeration value="ip-in-ip"/>
         <xs:enumeration value="ip-loose"/>
         <xs:enumeration value="media-specific"/>
         <xs:enumeration value="none"/>
       </xs:restriction>
     </xs:simpleType>

     <xs:simpleType name="policyValue">
       <xs:restriction base="xs:string">
         <xs:enumeration value="mandatory"/>
         <xs:enumeration value="allow"/>
         <xs:enumeration value="disallow"/>
       </xs:restriction>
     </xs:simpleType>


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     <xs:simpleType name="directionValue">
       <xs:restriction base="xs:string">
         <xs:enumeration value="sendrecv"/>
         <xs:enumeration value="sendonly"/>
         <xs:enumeration value="recvonly"/>
       </xs:restriction>
     </xs:simpleType>

   </xs:schema>

6.  Security Considerations

   Session policy information can be sensitive information.  The
   protocol used to distribute it SHOULD ensure privacy, message
   integrity and authentication.  Furthermore, the protocol SHOULD
   provide access controls which restrict who can see who else's session
   policy information.

7.  IANA Considerations

   This document registers a new MIME type,
   application/session-policy+xml, and registers a new XML namespace.

7.1  MIME Registration for application/session-policy+xml

   MIME media type name: application

   MIME subtype name: session-policy+xml

   Mandatory parameters: none

   Optional parameters: Same as charset parameter application/xml as
   specified in RFC 3023 [10].

   Encoding considerations: Same as encoding considerations of
   application/xml as specified in RFC 3023 [10].

   Security considerations: See Section 10 of RFC 3023 [10] and Section
   6 of this specification.

   Interoperability considerations: none.

   Published specification: This document.

   Applications which use this media type: This document type has been
   used to download the session policy of a domain to SIP user agents.


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   Additional Information:

   Magic Number: None

   File Extension: .wif or .xml

   Macintosh file type code: "TEXT"

   Personal and email address for further information: Volker Hilt,
   <volkerh@bell-labs.com>

   Intended usage: COMMON

   Author/Change controller: The IETF.

7.2  URN Sub-Namespace Registration for
    urn:ietf:params:xml:ns:sessionpolicy

   This section registers a new XML namespace, as per the guidelines in
   [6]

   URI: The URI for this namespace is
   urn:ietf:params:xml:ns:sessionpolicy.

   Registrant Contact: IETF, SIPPING working group, <sipping@ietf.org>,
   Volker Hilt, <volkerh@bell-labs.com>

           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>Session Policy Namespace</title>
                </head>
                <body>
                  <h1>Namespace for Session Policy Information</h1>
                  <h2>urn:ietf:params:xml:ns:sessionpolicy</h2>
                  <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
                </body>
                </html>
                END


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8  References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
         Levels", BCP 14, RFC 2119, March 1997.

   [2]   Handley, M., Jacobson, V. and C. Perkins, "SDP: Session
         Description Protocol", draft-ietf-mmusic-sdp-new-20 (work in
         progress), September 2004.

   [3]   Hilt, V., Camarillo, G. and J. Rosenberg, "A Framework for
         Session-Specific Session Policies in the Session Initiation
         Protocol (SIP)", draft-hilt-sipping-session-spec-policy-01
         (work in progress), October 2004.

   [4]   Hilt, V., Rosenberg, J. and G. Camarillo, "Media Type Extension
         Negotiation in the Session Initiation Protocol (SIP) Accept
         Header Field", draft-hilt-sip-ext-neg-00 (work in progress),
         January 2005.

   [5]   Hollander, D., Bray, T. and A. Layman, "Namespaces in XML", W3C
         REC REC-xml-names-19990114, January 1999.

   [6]   Mealling, M., "The IETF XML Registry",
         draft-mealling-iana-xmlns-registry-05 (work in progress), June
         2003.

   [7]   Levin, O. and G. Camarillo, "The SDP (Session Description
         Protocol) Label Attribute",
         draft-ietf-mmusic-sdp-media-label-01 (work in progress),
         January 2005.

   [8]   Moats, R., "URN Syntax", RFC 2141, May 1997.

   [9]   Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
         August 1999.

   [10]  Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
         3023, January 2001.

   [11]  Perkins, C., "IP Encapsulation within IP", RFC 2003, October
         1996.

   [12]  Petrie, D., "A Framework for Session Initiation Protocol User
         Agent Profile Delivery", draft-ietf-sipping-config-framework-05
         (work in progress), October 2004.

   [13]  Petrie, D., "A Schema for Session Initiation Protocol User
         Agent Profile Data Sets",


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         draft-petrie-sipping-profile-datasets-00 (work in progress),
         July 2004.

   [14]  Rosenberg, J., "Requirements for Session Policy for the Session
         Initiation Protocol (SIP)",
         draft-ietf-sipping-session-policy-req-02 (work in progress),
         July 2004.

   [15]  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.

   [16]  Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T. and E.
         Maler, "Extensible Markup Language (XML) 1.0 (Third Edition)",
         W3C REC REC-xml-20040204, February 2004.

Authors' Addresses

   Volker Hilt
   Bell Labs/Lucent Technologies
   101 Crawfords Corner Rd
   Holmdel, NJ  07733
   USA

   EMail: volkerh@bell-labs.com

   Gonzalo Camarillo
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   EMail: Gonzalo.Camarillo@ericsson.com

   Jonathan Rosenberg
   Cisco Systems
   600 Lanidex Plaza
   Parsippany, NJ  07054
   USA

   EMail: jdrosen@cisco.com

Appendix A.  Acknowledgements

   Many thanks to Allison Mankin for the discussions and the suggestions


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   for this draft.  Many thanks also to Dan Petrie and Martin Dolly.

























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