SIPPING Working Group V. Hilt
Internet-Draft Bell Labs/Alcatel-Lucent
Intended status: Standards Track D. Worley
Expires: August 6, 2011 Avaya Inc.
G. Camarillo
Ericsson
J. Rosenberg
jdrosen.net
February 2, 2011
A User Agent Profile Data Set for Media Policy
draft-ietf-sipping-media-policy-dataset-11
Abstract
This specification defines a document format for the media properties
of Session Initiation Protocol (SIP) sessions. Examples for media
properties are the codecs or media types used in a session. This
document format is based on XML and can be used to describe the
properties of a specific SIP session or to define policies that are
then applied to SIP sessions.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 6, 2011.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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Table of Contents
1. Open Revision Items . . . . . . . . . . . . . . . . . . . . . 4
1.1. Media Types . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.1. Require Registration . . . . . . . . . . . . . . . . . 4
1.1.2. Terminology . . . . . . . . . . . . . . . . . . . . . 4
1.1.3. Rename the <mime-type> child of <codec> . . . . . . . 4
1.2. Remove reference to uaprofile.rng . . . . . . . . . . . . 4
1.3. Remove <property-set> . . . . . . . . . . . . . . . . . . 5
1.4. Specifying Sets . . . . . . . . . . . . . . . . . . . . . 5
1.5. Specifying Bandwidth Limitations . . . . . . . . . . . . . 5
1.6. Rejecting a media stream . . . . . . . . . . . . . . . . . 5
1.7. The implied boolean logic of policy operations . . . . . . 6
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. Media Policy Dataset Format . . . . . . . . . . . . . . . . . 9
4.1. Namespace and Media Type . . . . . . . . . . . . . . . . . 9
4.2. Extensibility . . . . . . . . . . . . . . . . . . . . . . 9
4.3. Attributes . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3.1. The 'visibility' Attribute . . . . . . . . . . . . . . 10
4.3.2. The 'direction' Attributes . . . . . . . . . . . . . . 10
4.3.3. The 'q' Attribute . . . . . . . . . . . . . . . . . . 10
4.3.4. The 'label' Attribute . . . . . . . . . . . . . . . . 11
5. Session Info Documents . . . . . . . . . . . . . . . . . . . . 11
5.1. Mapping SDP to Session Info Documents . . . . . . . . . . 12
5.2. The <session-info> Element . . . . . . . . . . . . . . . . 12
5.3. The <streams> Element . . . . . . . . . . . . . . . . . . 12
5.3.1. The <stream> Element . . . . . . . . . . . . . . . . . 13
5.4. The <media-intermediaries> Element . . . . . . . . . . . . 14
5.4.1. The <fixed-intermediary> Element . . . . . . . . . . . 14
5.4.2. The <turn-intermediary> Element . . . . . . . . . . . 15
5.4.3. The <msrp-intermediary> Element . . . . . . . . . . . 16
6. Session Policy Documents . . . . . . . . . . . . . . . . . . . 16
6.1. Merging Session Policies . . . . . . . . . . . . . . . . . 17
6.1.1. Single Value Selection . . . . . . . . . . . . . . . . 17
6.1.2. Merging Sets . . . . . . . . . . . . . . . . . . . . . 17
6.1.3. Local Policy Server Selection . . . . . . . . . . . . 18
6.2. The <session-policy> Element . . . . . . . . . . . . . . . 18
6.3. The <media-types-allowed> Element . . . . . . . . . . . . 19
6.4. The <media-types-excluded> Element . . . . . . . . . . . . 19
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6.5. The <codecs-allowed> Element . . . . . . . . . . . . . . . 20
6.6. The <codecs-excluded> Element . . . . . . . . . . . . . . 20
6.7. The <local-ports> Element . . . . . . . . . . . . . . . . 21
7. Common Media Policy Dataset Elements . . . . . . . . . . . . . 21
7.1. The <media-type> Element . . . . . . . . . . . . . . . . . 21
7.2. The <codec> Element . . . . . . . . . . . . . . . . . . . 21
7.2.1. The <mime-type> Element . . . . . . . . . . . . . . . 22
7.2.2. The <mime-parameter> Element . . . . . . . . . . . . . 22
7.3. The <max-bw> Element . . . . . . . . . . . . . . . . . . . 22
7.4. The <max-session-bw> Element . . . . . . . . . . . . . . . 23
7.5. The <max-stream-bw> Element . . . . . . . . . . . . . . . 23
7.6. The <qos-dscp> Element . . . . . . . . . . . . . . . . . . 24
7.7. The <context> Element . . . . . . . . . . . . . . . . . . 25
7.7.1. The <policy-server-URI> Element . . . . . . . . . . . 25
7.7.2. The <contact> Element . . . . . . . . . . . . . . . . 25
7.7.3. The <info> Element . . . . . . . . . . . . . . . . . . 26
7.7.4. The <request-URI> Element . . . . . . . . . . . . . . 26
7.7.5. The <token> Element . . . . . . . . . . . . . . . . . 26
7.8. Other Session Properties . . . . . . . . . . . . . . . . . 26
8. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.1. Session Policy Documents . . . . . . . . . . . . . . . . . 27
8.2. Session Information Documents . . . . . . . . . . . . . . 27
8.2.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . 27
8.2.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . 28
9. Relax NG Definition . . . . . . . . . . . . . . . . . . . . . 30
10. Security Considerations . . . . . . . . . . . . . . . . . . . 37
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
11.1. Media Type Registration . . . . . . . . . . . . . . . . . 37
11.2. URN Sub-Namespace Registration . . . . . . . . . . . . . . 38
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
12.1. Normative References . . . . . . . . . . . . . . . . . . . 38
12.2. Informative References . . . . . . . . . . . . . . . . . . 40
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40
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1. Open Revision Items
This version of this Internet-Draft is largely the same as the
previous version. It has been submitted primarily to maintain the
draft as active. A number of significant open issues are described
in this section.
1.1. Media Types
1.1.1. Require Registration
In -10, all media type names that are mentioned in a MPDF are
explicitly required to be IANA-registered. Technically, this means
that experimental or private-use types can not be used, even in
situations where all participants are aware of non-registered media
types. In practice, people will go ahead and use them anyway. I am
proposing to remove the "registered" requirement.
1.1.2. Terminology
In a number of places, media types are called "MIME types". The
latter is common usage, but it is not official, and as RFC 4288 makes
clear, media types are independent of their use within MIME. I've
fixed the wording of the draft in a number of places to correct this.
1.1.3. Rename the <mime-type> child of <codec>
There is an element <mime-type> that is a child of the <codec>
element that carries a media type and subtype. The natural fix would
be to change this to <media-type>, but there is already an element of
that name that is a child of <stream> that carries a media type
(without subtype). I would like a name that means "media type and
subtype", but I can't think of a short one. Suggestions?
1.2. Remove reference to uaprofile.rng
The Relax NG schema given in draft-ietf-sipping-media-policy-dataset
includes "uaprofile.rng". As far as I can figure out, uaprofile.rng
is the schema defined in draft-ietf-sipping-profile-datasets, which
has been abandoned. So we need to remove the reference to
uaprofile.rng. It's possible that there are things defined in that
schema that need to be either deleted from
draft-ietf-sipping-media-policy-dataset, or copied from the abandoned
draft into the schema in draft-ietf-sipping-media-policy-dataset.
If anyone has further information about this, please tell me.
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1.3. Remove <property-set>
I have updated the text of draft-ietf-sipping-media-policy-dataset-11
to consistently use "property-set" rather than sometimes using
"property_set". However, it seems to me that the <property-set>
element serves no use (now that sipping-profile-datasets has been
abandoned). The draft says that each <session-info> and <session-
policy> appears in a <property-set>, and <property-set> can contain
more than one of each. But there seems to be no practical use for
this grouping; the semantics of <session-info> and <session-policy>
is completely standalone.
So I am proposing eliminating the <property-set> element entirely,
making <session-info> and <session-policy> into top-level elements.
1.4. Specifying Sets
There are many properties for which the values are sets of primitive
values. The current syntax for specifying sets is awkward. In
addition, it is not permitted to specify a set containing zero
elements. Sessions containing empty sets are not useful to write,
but it is easy to generate them when applying a policy to a <session-
info>. So the syntax for set values needs to be updated.
1.5. Specifying Bandwidth Limitations
Looking at the XML of draft-ietf-sipping-media-policy-dataset, I see
this paragraph:
<!--
<t>If a b= line is present for a media stream, this line MUST be
used to create the bandwidth elements.</t>
-->
SDP provides "b=" lines for specifying bandwidth limitations.
Similarly, MPD provides <max-bw>, <max-session-bw>, and
<max-stream-bw> elements, and the draft states that they are
equivalent to various forms of the b= line. Should we require that
when SDP is translated into MPD that the bandwidth limitations be
translated?
1.6. Rejecting a media stream
In draft-ietf-sipping-media-policy-dataset-10 there is no explicit
way to indicate that a stream has been rejected (which is needed to
correspond to an m= line in SDP where the port number is 0).
Implicitly, this can be done by setting the port number in the
<local-host-port> or <remote-host-port> to 0. But that is pretty
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ugly. I propose that we introduce an attribute of the <stream>
element to indicate that a stream has been rejected/disabled:
<stream enabled="no">
The default value of "enabled" would be "yes".
This resolves the problem of how a policy server would modify a
<session-info> to make it conform to a policy if one of the <stream>s
contradicted the policy: The policy server would put enabled="no"
onto the <stream>.
For consistency, a policy server could effectively reject a proposed
session by rejecting all of the streams within it. This would be
slightly different than rejecting the session as a whole by returning
an empty session-info document, <session-info/>. This distinction
corresponds to the difference between an SDP offer/answer negotiation
failing, and the negotiation succeeding but the answer rejecting all
the m= lines in the SDP.
1.7. The implied boolean logic of policy operations
I am starting work on a messy part of the media policy dataset
definition: Specifying the logic when a policy is applied to a
session-info, and also specifying how two policies are combined to
apply jointly to session-infos. The goal is to implement one's
intuitive expectations while introducing as few special cases as
possible.
My current analysis is:
o The primary operation is applying a session-policy to a session-
info to produce a possibly more restricted session-info. This is
done by applying the session-policy to each stream in turn, which
may "restrict" the stream (in regard to bandwidth, codecs, etc.).
o A stream may be restricted to the point that it permits no media
whatsoever. Such "null" streams are all logically equivalent,
although a null stream can be represented in many different ways.
When translated back into SDP, a null stream becomes a rejected m=
line.
o The different <stream> elements in a session-policy are
effectively ORed together, in that the policy intends to permit
any stream that conforms to *any one* of the <stream> elements.
This is necessary because e.g. a session-policy can contain one
<stream> that specifies audio media and restricts the codecs
permitted for audio, and another <stream> that specifies video
media and restricts the codecs permitted for video.
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o Thus, applying a session-policy to a stream involves applying each
session-policy <stream> to the stream, and then choosing the
"best" result. In practice, we expect that the streams admitted
by the session-policy <stream> elements to be disjoint (e.g., one
is for audio, one is for video), so the result of applying any but
one <stream> will be a null stream, and the "best" result will be
the only non-null result.
o The alternative strategy of "unioning" the results of applying
each <stream> element cannot be used because it can allow the
resulting session to exceed all of the <stream> element policies.
Consider the policy
<streams>
<stream> codecs: audio/foo, bandwidth: 10 </stream>
<stream> codecs: audio/foo,audio/bar, bandwidth: 1 </stream>
</streams>
applied to the requested stream "codecs: audio/foo,audio/bar,
bandwidth: 10". The result of restricting with the first <stream>
is "codecs: audio/foo, bandwidth: 10" and the result of
restricting with the second <stream> is "codecs: audio/foo,audio/
bar, bandwidth: 1". The union of the two (the "smallest" stream
that contains them both) is "codecs: audio/foo,audio/bar,
bandwidth: 10", which is not allowed by either <stream>.
o Within this context, combining two policies to form a joint policy
that enforces both their restrictions simultaneously is simple:
The resulting policy is made by "intersecting" all possible pairs
of <stream>s, one from the first policy and one from the second
policy. (Intersections that result in null policies can be
dropped from the result.)
o I haven't studied the role of the directional attributes yet, but
currently I believe that a bidirectional session-info <stream> can
be treated as an abbreviation for two session-info <stream>s, one
in each direction, and a bidirectional session-policy <stream> can
be treated similarly. Or, directionality can be treated as an
attribute with two possible values, *with identical results*.
2. Introduction
The Framework for Session Initiation Protocol (SIP) [RFC3261] User
Agent Profile Delivery [I-D.ietf-sipping-config-framework] and the
Framework for SIP Session Policies
[I-D.ietf-sip-session-policy-framework] define mechanisms to convey
session policies and configuration information from a network server
to a user agent. An important piece of the information conveyed to
the user agent relates to the media properties of the SIP sessions
set up by the user agent. Examples for these media properties are
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the codecs and media types used, the media-intermediaries to be
traversed or the maximum bandwidth available for media streams.
This specification defines a document format for media properties of
SIP sessions, the Media Policy Dataset Format (MPDF). This format
can be used in two ways: first, it can be used to describe the
properties of a given SIP session (e.g., the media types and codecs
used). These MPDF documents are called session info documents and
they are usually created based on the session description of a
session. Second, the MPDF format can be used to define policies for
SIP sessions in a session policy document. A session policy document
defines properties for a session (e.g., the media types allowed in a
session), independent of a specific session description.
If used with the Framework for SIP Session Policies
[I-D.ietf-sip-session-policy-framework], session info documents are
used in conjunction with session-specific policies. A session info
document is created by a UA based on the current session description
and submitted to the policy server. The policy server examines the
session info document, modifies it if necessary (e.g., by removing
video streams if video is not permitted) and returns the possibly
modified session info document to the UA. Session policy documents
on the other hand are used to describe session-independent policies
that can be submitted to the UA independent of a specific session.
The two types of MPDF documents, session information and session
policy documents, share the same set of XML elements to describe
session properties. Since these elements are used in different
contexts for session info and session policy documents, two different
root elements exist for the two document types: <session-info> is the
root element for session information documents and <session-policy>
is the root element for session policy documents.
A user agent can receive multiple session policy documents from
different sources. This can lead to a situation in which the user
agent needs to apply multiple session policy documents to the same
session. This standard specifies merging rules for those XML
elements that can be present in session policy documents. It should
be noted that these merging rules are part of the semantics of a
session policy XML element. User agents implement the merging rules
as part of implementing the element semantics. As a consequence, it
is not possible to build an entity that can mechanically merge two
session policy documents without understanding the semantics of all
elements in the input documents.
Merging rules are not needed for elements of session information
documents since they are created by one source and describe a
specific session.
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3. 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 RFC 2119 [RFC2119].
4. Media Policy Dataset Format
This section discusses fundamental properties of the Media Policy
Dataset Format (MPDF).
4.1. Namespace and Media Type
The MPDF format is based on XML [W3C.REC-xml-20040204]. A MPDF
document MUST be well-formed and MUST be valid according to schemas,
including extension schemas, available to the validator and
applicable to the XML document. MPDF documents MUST be based on XML
1.0 and MUST be encoded using UTF-8.
MPDF makes use of XML namespaces [W3C.REC-xml-names-19990114]. The
namespace URIs for schemas defined in this specification are URNs
[RFC2141], using the namespace identifier 'ietf' defined by [RFC2648]
and extended by [RFC3688]. The namespace URN for the MPDF schema is:
urn:ietf:params:xml:ns:mediadataset
The media type for the Media Policy Dataset Format is:
application/media-policy-dataset+xml
4.2. Extensibility
The MPDF format can be extended using XML extension mechanisms if
additional media properties are needed. In particular, elements from
different XML namespaces MAY be present within a MPDF document for
the purposes of extensibility; elements or attributes from unknown
namespaces MUST be ignored.
4.3. Attributes
The following attributes can be used with elements of the MPDF
format. For each MPDF element it is defined, which of these
attributes can be used. Attributes that are not defined for an
element MUST be ignored.
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4.3.1. The 'visibility' Attribute
The attribute "visibility" specifies whether or not the user agent is
permitted to display the property value to the user. This is used to
hide setting values that the administrator may not want the user to
see or know. The "visibility" attribute has two possible values:
o visible: specifies that display of the property value is not
restricted. This is the default value of the attribute if it is
not specified.
o hidden: Specifies that the user agent SHOULD NOT display the
property value. Display of the property value may be allowed
using special administrative interfaces, but is not appropriate to
the ordinary user.
4.3.2. The 'direction' Attributes
Some properties are unidirectional and only apply to messages or data
streams transmitted into one direction. For example, a property for
media streams can be restricted to outgoing media streams only.
Unidirectional properties can be expressed by adding a 'direction'
attribute to the respective element.
The 'direction' attribute can have the following values:
o recvonly: the property only applies to incoming messages/streams.
o sendonly: the property only applies to outgoing messages/streams.
o sendrecv: the property applies to messages/streams in both
directions. This is the default value that is used if the
'direction' attribute is omitted.
4.3.3. The 'q' Attribute
It should be possible to express a preference for a certain value, if
multiple values are allowed within a property. For example, it
should be possible to express that the codecs G.711 and G.729 are
allowed, but G.711 is preferred. Preferences can be expressed by
adding a 'q' attribute to a property element. Elements derived from
the "setting" element for which multiple occurrences and values are
allowed SHOULD have a "q" attribute if the order is significant.
Typically these elements are contained in an element derived from the
"setting_container" element. The 'q' attribute is only meaningful if
the 'policy' attribute set to 'allowed'. It must be ignored in all
other cases.
An element with a higher 'q' value is preferred over one with a lower
'q' value. 'q' attribute values range from 0 to 1. The default value
is 0.5.
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4.3.4. The 'label' Attribute
Some properties only apply to a specific media stream. The stream to
which a property applies MUST be identifiable through a label
[RFC4574]. Per-stream properties can be expressed by adding a
'label' attribute to the respective element. Such a property only
applies to the identified stream. If there is no stream with this
label, the element must be ignored.
Per-stream properties require that the labels of media streams are
known to the creator of a document (i.e., the profile delivery/policy
server). These labels are part of the session description.
5. Session Info Documents
Session info documents describe key properties of a SIP session such
as the media streams used in the session. Session info documents are
typically created based on an SDP [RFC4566] session description or an
SDP offer/answer pair [RFC3264].
Session info documents can be used for session-specific policies
[I-D.ietf-sip-session-policy-framework]. In this usage, a UA creates
a session info document based on its SDP description(s) and sends
this document to the policy server. The policy server modifies this
document according to the policies that apply to the described
session and returns a version of the session info document that is
compliant to the policies. For example, if video streams are not
permissible under current policies and the UA submits a session info
document that contains a video stream, the policy server will disable
the video stream in the session info document that it returns to the
UA.
Session info documents use the <session-info> root element. They use
elements described in this section and common elements described in
Section 7.
Elements that are only present in session info document do not
require merging rules. If used in the context of session-specific
policies, session info documents are sent to one policy server at a
time only, therefore a UA does not need to merge multiple session
info documents into one. A policy server needs to modify a session
info document it has received according to its policies. The
modification of session info documents is determined by the local
policies of the policy server and outside the scope of this standard.
A policy server can completely reject a session by returning an
session info document with an empty <session-info> element:
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<session-info><\session-info>
5.1. Mapping SDP to Session Info Documents
If a UA has an SDP offer as well as an answer [RFC3264] and wants to
create a session info document, the UA MUST use the answer to fill in
the elements of the session info document except for the remote-host-
port and local-host-port elements, which are taken from the remote
and local session description respectively. (The local session
description is the one sent by the UA; the remote session description
is the one received from the remote UA.)
The following rules describe the creation of session info documents
based on SDP description(s) for a few exemplary elements. Other
elements are created following the same principles.
A UA MUST create a separate <stream> element for each m= line in an
SDP description; the order of the <stream> elements corresponds to
the order of the m= lines. The UA MUST insert the media type from
the m= line into a <media-type> element and MUST create a <codec>
element for each codec listed in the m= line.
The UA MUST create a <local-host-port> element for each stream using
the port taken from the m= line and the address from the
corresponding c= line of the local session description. The UA MUST
create a <remote-host-port> element using the port and address from
the m= and c= lines for the same stream taken from the remote session
description if this session description is available.
The mapping from a session info document to a SDP description follows
the same rules in the reverse direction.
5.2. The <session-info> Element
The <session-info> element describes the properties of a specific SIP
session. The <session-info> element MAY contain one optional
<streams>, <context> and multiple (including zero) <max-bw>, <max-
session-bw>, <max-stream-bw>, <media-intermediaries> and <qos-dscp>
elements as well as elements from other namespaces. The MPDF
elements are defined in Section 7.
5.3. The <streams> Element
The <streams> element is a container that is used to describe the
media streams used in a session. A <streams> element contains zero
or more <stream> elements. Each <stream> element describes the
properties (e.g., media type, codecs and IP addresses and ports) of a
single media stream.
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5.3.1. The <stream> Element
The <stream> element describes a specific media stream. It contains
the media type, codecs and the hostname(s) or IP address(es) and
port(s) of this stream.
The hostname(s) or IP address(es) and port number(s) of a stream
correspond to the ones listed in the session description(s). A UA
that generates a <stream> element MUST insert the hostname/port found
in the local session description for this media stream into the
local-host-port element. The UA MUST insert the hostname/port of the
remote session description into the remote-host-port element, if the
remote session description is available to the UA. If not, the UA
generates a stream element that only contains the local-host-port
element.
This element MAY have the following attributes (see Section 4.3):
direction, label.
The label attribute is used to identify a specific media stream in a
session description. The value of the label attribute is a token.
The token can be chosen freely, however, it MUST be unique among all
<stream> element in a session-info document. If a label attribute
[RFC4574] is present in the SDP description, its value MUST be used
as the label attribute value of the corresponding <stream> element.
The <stream> element MUST contain one <media-type> element, one or
more <codec> elements and one <local-host-port> element. The
<stream> element MAY contain one <remote-host-port> element.
5.3.1.1. The <local-host-port> Element
The <local-host-port> element contains the hostname or IP address and
the receiving port number of the media stream in the local session
description. The hostname or IP address is separated from the port
by a ":". An example is: "host.example.com:49562".
The hostname or IP address of element is found in the c= element for
the stream in the local SDP description. The port number is found in
the m= element.
5.3.1.2. The <remote-host-port> Element
The <remote-host-port> element is structured exactly as the <local-
host-port> element. However, it identifies the hostname or IP
address and receiving port number of the media stream in the remote
session description.
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5.4. The <media-intermediaries> Element
The <media-intermediaries> element expresses a policy for routing a
media stream through a media intermediary. The purpose of the
<media-intermediaries> element is to tell the UA to send a media
stream through one (or a chain of) media intermediaries. Instead of
sending the media directly to its final destination, the UA specifies
a source route, which touches each intermediary and then reaches the
final recipient. If there are N hops, including the final recipient,
there needs to be a way for the media stream to specify N
destinations.
The <media-intermediaries> element is a container that lists all
media intermediaries to be traversed. Media intermediaries should be
traversed in the order in which they appear in this list. The
topmost entry should be traversed first, the last entry should be
traversed last.
Different types of intermediaries exist. These intermediaries are
not necessarily interoperable and it may not be possible to chain
them in an arbitrary order. A <media-intermediaries> element SHOULD
therefore only contain intermediary elements of the same type.
This element MAY have the following attributes (see Section 4.3):
direction.
Multiple <media-intermediaries> elements MAY only be present in a
container if each applies to a different set of streams (e.g., one
<media-intermediaries> element for incoming and one for outgoing
streams). The <media-intermediaries> element MUST contain one or
more elements defining a specific media intermediary, such as <fixed-
intermediary> or <turn-intermediary>.
Note: it is not intended that the <media-intermediaries> element
replaces connectivity discovery mechanisms such as ICE. Instead
of finding media relays that provide connectivity, this element
defines a policy for media intermediaries that should be
traversed. The set of intermediaries defined in the <media-
intermediaries> element and the ones discovered through ICE may
overlap but don't have to.
5.4.1. The <fixed-intermediary> Element
A fixed intermediary relies on pre-configured forwarding rules. The
user agent simply sends media to the first media intermediary listed.
It can assume that this media intermediary has been pre-configured
with a forwarding rule for the media stream and knows where to
forward the packets to. The configuration of forwarding rules in the
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intermediary must be done through other means.
The contents of a <fixed-intermediary> element MUST be echoed to all
policy servers that provide policies for a session. I.e., if
multiple policy servers provide policies for the same session, this
element needs to be forwarded to all of them, possibly in a second
round of session-specific policy subscriptions as described in
[I-D.ietf-sip-session-policy-framework] in section Contacting the
Policy Server.
The <fixed-intermediary> element MUST contain one <int-host-port>
element and MAY contain multiple optional <int-addl-port> elements.
5.4.1.1. The <int-host-port> Element
The <int-host-port> element contains the hostname or IP address and
port number of a media intermediary. The UA uses this hostname/IP
address and port to send its media streams to the intermediary. The
hostname or IP address is separated from the port by a ":".
If a protocol uses multiple subsequent ports (e.g., RTP), the lowest
port number SHOULD be included in the <int-host-port> element. All
additional port numbers SHOULD be identified in <int-addl-port>
elements.
5.4.1.2. The <int-addl-port> Element
If a protocol uses multiple subsequent ports (e.g., RTP), the lowest
port number SHOULD be included in the <int-host-port> element. All
additional port numbers SHOULD be identified in <int-addl-port>
elements.
5.4.2. The <turn-intermediary> Element
The TURN [RFC5766] protocol provides a mechanism for inserting a
relay into the media path. Although the main purpose of TURN is NAT
traversal, it is possible for a TURN relay to perform other media
intermediary functionalities. The user agent establishes a binding
on the TURN server and uses this binding to transmit and receive
media.
The <turn-intermediary> element MUST contain one <int-host-port>
element and MAY contain multiple optional <int-addl-port> elements
and zero or one each of the <shared-secret>, <user>, and <transport>
elements. If no <transport> element is present, UDP is assumed.
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5.4.2.1. The <shared-secret> Element
The <shared-secret> element contains the shared secret needed to
authenticate at the media intermediary.
5.4.2.2. The <user> element
The <user> element contains the user ID needed to authenticate to the
media intermediary.
5.4.2.3. The <transport> Element
The <transport> element contains the name of the transport to be used
for communicating with the TURN server. This document defines the
values "tcp" and "udp" for use in the <transport> element. Other
specifications may define additional values.
5.4.3. The <msrp-intermediary> Element
The MSRP Relay Extensions [RFC4976] define a means for incorporating
relays into the media path of an MSRP [RFC4975] session. MSRP is
explicitly designed for a variety of purposes, including policy
enforcement.
The <msrp-intermediary> element MUST contain one <msrp-uri> element,
and may contain zero or one each of the <shared-secret> and <user>
elements.
5.4.3.1. The <msrp-uri> Element
The <msrp-uri> element contains a URI that indicates the MSRP server
to use for an intermediary. The UA uses this URI to authenticate
with the MSRP relay, and then uses the URI it learns through that
authentication process for any MSRP media it sends or receives. Only
URIs with a scheme of "msrps:" are valid in the <msrp-uri> element.
6. Session Policy Documents
Session policy documents describe policies for SIP sessions. Session
policy documents are independent of any specific session description
and express general policies for SIP sessions. A session policy
document is used to determine if a SIP session is policy conformant
and can be used to modify the session, if needed, to conform to the
described policies.
Session policy documents can be used to encode session-independent
policies [I-D.ietf-sip-session-policy-framework]. In this usage, a
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policy server creates a session policy document and passes this
document to a UA. The UA applies the policies defined to the SIP
sessions it is establishing. For example, a session policy document
can contain an element that prohibits the use of video. To set up a
session that is compliant to this policy, a UA does not include the
media type video in its SDP offer or answer.
Session policy documents use the <session-policy> root element. They
use elements described in this section and common elements described
in Section 7.
6.1. Merging Session Policies
A UA may receive session policy documents from multiple sources;
multiple session policy documents can be merged into a single session
policy document which expresses the logical AND of the policies.
6.1.1. Single Value Selection
Properties that have a single value (e.g., the maximum bandwidth
allowed) require that a common value is determined for this property
during the merging process. The merging rules for determining this
value need to be defined individually for each element in the schema
definition (e.g., select the lowest maximum bandwidth).
6.1.2. Merging Sets
The media-types-allowed, media-types-excluded, codecs-allowed and
codecs-excluded are containers that contain a set of media-types/
codecs. The values defined in these containers need to be merged to
determine the set of media-types/codecs that are permissible in a
session.
To merge the media-types-* and codecs-* containers a UA needs to
apply all containers it has received one after the other the set of
media-types/codecs it supports. After applying media-types-*/
codecs-* elements, the UA has the list of media-types/codecs that are
allowed in a session. The containers can be applied in any order.
However, each time a container is applied to the set of media-types/
codecs allowed, this set MUST stay the same or be reduced. Media-
types/codecs cannot be added during this process.
The following example illustrates the merging process for two data
sets. In this example, the UA supports the following set of audio
codecs: PCMA, PCMU and G729. After applying session policy document
1, the UA removes PCMA as it is disallowed by this policy. The
remaining set of codecs is: PCMU and G729. Session policy document 2
disallows all codecs that are not listed. After applying this
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policy, the set of codecs allowed is: G729.
Session Policy Document 1:
<codecs-excluded>
<codec><mime-type>audio/PCMA</mime-type></codec>
</codecs>
Session Policy Document 2:
<codecs-allowed>
<codec><mime-type>audio/PCMA</mime-type></codec>
<codec><mime-type>audio/G729</mime-type></codec>
</codecs>
It is possible that two session policy documents define non-
overlapping sets of allowed media-types or codecs. The resulting
merged set would be empty, which is illegal according to the schema
definition of the media-types/codecs element. This constitutes a
conflict that cannot be resolved automatically. If these properties
are enforced by both networks, the UA will not be able to set up a
session.
The combined set of media-types/codecs MUST again be valid and well-
formed according to the schema definitions. A conflict occurs if the
combined property set is not a well-formed document after the merging
process is completed.
6.1.3. Local Policy Server Selection
Some properties require that only values from the local policy server
are used. The local policy server is the policy server that is in
the local domain of the user agent.
If policy documents are delivered through the configuration framework
[I-D.ietf-sipping-config-framework], the value received through a
subscription using the "local-network" profile-type is used. Values
received through other profile-type subscriptions are discarded.
If policy documents are delivered through the session-specific policy
mechanism [I-D.ietf-sip-session-policy-framework] the value received
from the policy server identified by the Local Policy Server URI are
used. Values received from other policy servers are discarded.
6.2. The <session-policy> Element
The <session-policy> element describes a policy that applies to SIP
sessions. The <session-policy> element MAY contain one optional
<context> and <local-ports> element and multiple (including zero)
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<media-types-allowed>, <media-types-excluded>, <codecs-allowed>,
<codecs-excluded>, <max-bw>, <max-session-bw>, <max-stream-bw> and
<qos-dscp> elements as well as elements from other namespaces. The
MPDF elements are defined in Section 7.
6.3. The <media-types-allowed> Element
The <media-types-allowed> element is a container that is used to
define the set of media types (e.g., audio, video) that are allowed
in a session. All media types that are not listed in this container
are not permitted in a session. A specific media type is allowed by
adding the corresponding <media-type> element to this container.
This element MAY have the following attributes (see Section 4.3):
direction, visibility.
Multiple <media-types-allowed> elements MAY only be present in a
container element if each applies to a different set of streams
(e.g., one <media-types-allowed> element for incoming and one for
outgoing streams). The <media-types-allowed> element MUST contain
one or more <media-type> elements.
A <media-types-allowed> element MUST NOT be used in a container that
contains a <media-types-excluded> element.
Merging of session-policy documents: <media-types-allowed>
containers are merged as described in "Merging Sets"
Section 6.1.2.
6.4. The <media-types-excluded> Element
The <media-types-excluded> element is a container that is used to
define the set of media types (e.g., audio, video) that are not
permitted in a session. All media types that are not listed in this
container are allowed and can be used in a session. A specific media
type is excluded from a session by adding the corresponding <media-
type> element to this container.
This element MAY have the following attributes (see Section 4.3):
direction, visibility.
Multiple <media-types-excluded> elements MAY only be present in a
container element if each applies to a different set of streams
(e.g., one <media-types-excluded> element for incoming and one for
outgoing streams). The <media-types-excluded> element MUST contain
one or more <media-type> elements.
A <media-types-excluded> element MUST NOT be used in a container that
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contains a <media-types-allowed> element.
Merging of session-policy documents: <media-types-excluded>
containers are merged as described in "Merging Sets"
Section 6.1.2.
6.5. The <codecs-allowed> Element
The <codecs-allowed> element is a container that is used to define
the set of codecs that may be used in a session. All codes not
listed in the <codecs-allowed> element are disallowed and MUST NOT be
used in a session. A policy MUST allow the use of at least one codec
per media type. A specific codec is allowed by adding the
corresponding <codec> element to this container.
The <codecs-allowed> element MAY have the following attributes (see
Section 4.3): direction, visibility.
Multiple <codecs-allowed> elements MAY only be present in a container
element if each applies to a different set of streams (e.g., one
<codecs-allowed> element for incoming and one for outgoing streams).
The <codecs-allowed> element MUST contain one or more <codec>
elements.
A <codecs-allowed> element MUST NOT be used in a container that
contains a <codecs-excluded> element.
Merging of session-policy documents: <codecs-allowed> containers
are merged as described in "Merging Sets" Section 6.1.2.
6.6. The <codecs-excluded> Element
The <codecs-excluded> element is a container that is used to define
the set of codecs that are disallowed in a session. All codes not
listed in the <codecs-excluded> element are permitted and MAY be used
in a session. A specific codec is disallowed by adding the
corresponding <codec> element to this container.
The <codecs-excluded> element MAY have the following attributes (see
Section 4.3): direction, visibility.
Multiple <codecs-excluded> elements MAY only be present in a
container element if each applies to a different set of streams
(e.g., one <codecs-excluded> element for incoming and one for
outgoing streams). The <codecs-excluded> element MUST contain one or
more <codec> elements.
A <codecs-excluded> element MUST NOT be used in a container that
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contains a <codecs-allowed> element.
Merging of session-policy documents: <codecs-excluded> containers
are merged as described in "Merging Sets" Section 6.1.2.
6.7. The <local-ports> Element
Domains often require that a user agent only uses ports in a certain
range for media streams. The <local-ports> element defines a policy
for the ports a user agent can use for media. The value of this
element consists of a start port and an end port separated by a "-".
The start/end port is the first/last port that can be used.
This element MAY have the following attributes (see Section 4.3):
visibility.
Merging of session-policy documents: the local domain of the user
agent has precedence over other domains and its local ports value
is used. During the merging process, <local-ports> element values
from local policy server selected as described in "Local Policy
Server Selection" Section 6.1.3 are used.
7. Common Media Policy Dataset Elements
This section describes common XML elements that are used in session
info and session policy documents to encode the media properties of
SIP sessions.
7.1. The <media-type> Element
The <media-type> element identifies a specific media type. The value
of this element MUST be the name of a media type, such as 'audio',
'video', 'text', or 'application'.
This element MAY have the following attribute (see Section 4.3): q.
If used in a session policy document inside a <media-types-allowed>
element, the media types defined MAY be used in a session. If used
in a session policy document inside a <media-types-excluded> element,
the media types defined MUST NOT be used in a session.
7.2. The <codec> Element
The <codec> element identifies a specific codec. The content of this
element MUST be a media type and subtype (e.g., audio/PCMA [RFC4856]
or video/H263 [RFC4629]), possibly with parameters.
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The <codec> element MAY have the following attribute (see
Section 4.3): q.
If used in a session policy document inside a <codecs-allowed>
element, the codec defined MAY be used in a session. If used in a
session policy document inside a <codecs-excluded> element, the codec
defined MUST NOT be used in a session.
The <codec> element MUST contain one <mime-type> element and MAY
contain multiple optional <mime-parameter> elements.
7.2.1. The <mime-type> Element
The <mime-type> element contains a media type and subtype that
identifies a codec. The value of this element MUST be a media type
and subtype [RFC4855] separated by a "/" (e.g., audio/PCMA, audio/
G726-16 [RFC4856] or video/H263 [RFC4629]).
7.2.2. The <mime-parameter> Element
The <mime-parameter> element may be needed for some codecs to
identify a particular encoding or profile. The value of this element
MUST be a name-value pair containing the name and the value of a
media type parameter for the codec [RFC4855]. The name and value are
separated by a "=". For example, the parameter "profile=0" can be
used to specify a specific profile for the codec "video/H263-2000"
[RFC4629].
7.3. The <max-bw> Element
The <max-bw> element defines the overall maximum bandwidth in
kilobits per second an entity can/will use for media streams at any
point in time. It defines an upper limit for the total bandwidth an
entity can/will use for the transmission of media streams. The limit
corresponds to the sum of the maximum session bandwidth of all
sessions a UA may set up in parallel.
The bandwidth limit given in the <max-bw> element includes the
bandwidth needed for lower-layer transport and network protocols
(e.g., UDP and IP).
The <max-bw> element MAY have the following attribute (see
Section 4.3): direction.
If used in a <session-policy> element, the <max-bw> element MAY have
the following additional attribute (see Section 4.3): visibility.
If the <max-bw> element occurs multiple times in a container element,
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each instance MUST apply to a different set of media streams (i.e.,
one <max-bw> element for outgoing and one for incoming streams).
Merging of session-policy documents: the lowest max-bw value is
used.
7.4. The <max-session-bw> Element
The <max-session-bw> element defines the maximum bandwidth in
kilobits per second an entity can/will use for media streams in the
described session. It defines an upper limit for the total bandwidth
of a single session. This limit corresponds to the sum of the
maximum stream bandwidth of all media streams in a session.
The bandwidth limit given in the <max-session-bw> element includes
the bandwidth needed for lower-layer transport and network protocols
(e.g., UDP and IP).
The value of the <max-session-bw> element is equivalent to the CT
bandwidth in the b= line of an SDP [RFC4566] announcement.
The <max-session-bw> element MAY have the following attribute (see
Section 4.3): direction.
If used in a <session-policy> element, the <max-session-bw> element
MAY have the following additional attribute (see Section 4.3):
visibility.
If the <max-session-bw> element occurs multiple times in a container
element, each instance MUST apply to a different set of media streams
(i.e., one <max-session-bw> element for outgoing and one for incoming
streams).
Merging of session-policy documents: the lowest max-session-bw
value is used.
7.5. The <max-stream-bw> Element
The <max-stream-bw> element defines the maximum bandwidth in kilobits
per second an entity can/will use for each media stream in the
described session.
The bandwidth limit given in the <max-stream-bw> element includes the
bandwidth needed for lower-layer transport and network protocols
(e.g., UDP and IP).
The value of the <max-stream-bw> element is equivalent to the AS
bandwidth in the b= line of an SDP [RFC4566] announcement.
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The <max-stream-bw> element MAY have the following attribute (see
Section 4.3): direction, media-type.
If used in a <session-policy> element, the <max-stream-bw> element
MAY have the following additional attribute (see Section 4.3):
visibility.
If used in a <session-info> element, the <max-stream-bw> element MAY
have the following additional attribute: label.
The media-type attribute is used to define that the <max-stream-bw>
element only applies to streams of a certain media type. For
example, it may only apply to audio streams. The value of the
'media-type' attribute MUST be the media type, such as 'audio',
'video', 'text', or 'application'.
The label attribute is used to define a bandwidth limit for a
specific media stream. The use of this attribute requires that the
<stream> element that represents the media stream to which this
bandwidth limit applies also has a label attribute. A
<max-stream-bw> element with a label attribute applies only to the
stream element that has a label attribute with the same value. If no
matching <stream> element exists, then the <max-stream-bw> element
MUST be ignored.
If the <max-stream-bw> element occurs multiple times in a container
element, each instance MUST apply to a different set of media streams
(i.e., one <max-stream-bw> element for outgoing and one for incoming
streams).
Merging of session-policy documents: the lowest max-stream-bw
value is used.
7.6. The <qos-dscp> Element
The <qos-dscp> element contains an Differentiated Services Codepoint
(DSCP) [RFC2474] value that should be used to populate the IP DS
field of media packets. The <qos-dscp> contains an integer value
that represents a 6 bit field and therefore ranges from 0 to 63.
This element MAY have the following attributes (see Section 4.3):
direction, media-type.
If used in a <session-policy> element, the <qos-dscp> element MAY
have the following additional attribute (see Section 4.3):
visibility.
The media-type attribute is used to define that <qos-dscp> element
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only applies to streams of a certain media type. For example, it may
only apply to audio streams. The value of the 'media-type' attribute
MUST be the name of a media type, such as 'audio', 'video', 'text',
or 'application'.
The <qos-dscp> element is optional and MAY occur multiple times
inside a container. If the <qos-dscp> element occurs multiple times,
each instance MUST apply to a different media stream (i.e., one <qos-
dscp> element for audio and one for video streams).
Merging of session-policy documents: the local domain of the user
agent has precedence over other domains and its DSCP value is
used. During the merging process, <qos-dscp> element values from
local policy server selected as described in "Local Policy Server
Selection" Section 6.1.3 are used.
7.7. The <context> Element
The <context> element provides context information about a session
policy or session information document.
The <context> element MAY contain multiple <contact> and one <info>
element.
If used in a <session-policy> element, the <context> element MAY also
contain a <policy-server-URI> element.
If used in a <session-info> element, the <context> element MAY also
contain a <request-URI> and a <token> element.
Merging of session-policy documents: the <context> element is not
subject to merging.
7.7.1. The <policy-server-URI> Element
The <policy-server-URI> element contains the URI of the policy server
that has issued this policy.
The <policy-server-URI> element is only defined inside a <session-
policy> element.
7.7.2. The <contact> Element
The <contact> element contains a contact address (e.g., a SIP URI or
email address) under which the issuer of this document can be
reached.
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7.7.3. The <info> Element
The <info> element provides a short textual description of the policy
or session that should be intelligible to the human user.
7.7.4. The <request-URI> Element
The <request-URI> element identifies the request-URI the dialog
initiating request of a session is sent to.
The <request-URI> element is only defined inside a <session-info>
element.
7.7.5. The <token> Element
The <token> element provides a mechanism for a policy server to
return an opaque token to a UA. This is sometimes needed to ensure
that all requests for a session are routed to the same policy server.
The use of this token is described in the Framework for SIP Session
Policies [I-D.ietf-sip-session-policy-framework].
The <token> element is only defined inside a <session-info> element.
7.8. Other Session Properties
A number of additional elements have been proposed for a media
property language. These elements are deemed to be outside the scope
of this format. However, they may be defined in extensions of MPDF
or other profile data sets.
o maximum number of streams
o maximum number of sessions
o maximum number of streams per session
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
8. Examples
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8.1. Session Policy Documents
The following example describes a session policy document that allows
the use of audio and video and prohibits the use of other media
types. It allows the use of any codec except G.723 and G.729.
<session-policy>
<context>
<policy-server-URI>policy@biloxi.example.com</policy-server-URI>
<contact>sip:policy_manager@example.com</contact>
<info>Access network policies</info>
</context>
<media-types-allowed>
<media-type>audio</media-type>
<media-type>video</media-type>
</media-types>
<codecs-excluded>
<codec><mime-type>audio/G729</mime-type></codec>
<codec><mime-type>audio/G723</mime-type></codec>
</codecs>
</session-policy>
8.2. Session Information Documents
The following examples contain session descriptions and the session
information documents that represent these sessions.
8.2.1. Example 1
In this example, a session info document is created based on one
session description. This session info document would be created,
for example, by a UA that has composed an offer and is now contacting
a policy server.
Local SDP session description:
v=0
o=alice 2890844526 2890844526 IN IP4 host.somewhere.example
s=
c=IN IP4 host.somewhere.example
t=0 0
m=audio 49562 RTP/AVP 0 1 3
a=rtpmap:0 PCMU/8000
a=rtpmap:1 1016/8000
a=rtpmap:3 GSM/8000
m=video 51234 RTP/AVP 31 34
a=rtpmap:31 H261/90000
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a=rtpmap:34 H263/90000
MPDF document:
<session-info>
<context>
<contact>sip:alice@somewhere.example</contact>
<info>session information</info>
</context>
<streams>
<stream>
<media-type>audio</media-type>
<codec><mime-type>audio/PCMU</mime-type></codec>
<codec><mime-type>audio/1016</mime-type></codec>
<codec><mime-type>audio/GSM</mime-type></codec>
<local-host-port>host.somewhere.example:49562</local-host-port>
</stream>
<stream>
<media-type>video</media-type>
<codec><mime-type>video/H261</mime-type></codec>
<codec><mime-type>video/H263</mime-type></codec>
<local-host-port>host.somewhere.example:51234</local-host-port>
</stream>
</streams>
</session-info>
8.2.2. Example 2
In this example, a session info document is created that represents
two session descriptions (i.e., an offer and answer). This session
info document would be created, for example, by a UA that has
received an answer from another UA and is now contacting a policy
server.
Local SDP session description:
v=0
o=alice 2890844526 2890844526 IN IP4 host.somewhere.example
s=
c=IN IP4 host.somewhere.example
t=0 0
m=audio 49562 RTP/AVP 0 1 3
a=rtpmap:0 PCMU/8000
a=rtpmap:1 1016/8000
a=rtpmap:3 GSM/8000
m=video 51234 RTP/AVP 31 34
a=rtpmap:31 H261/90000
a=rtpmap:34 H263/90000
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Remote SDP session description:
v=0
o=bob 2890844730 2890844730 IN IP4 host.anywhere.example
s=
c=IN IP4 host.anywhere.example
t=0 0
m=audio 52124 RTP/AVP 0 3
a=rtpmap:0 PCMU/8000
a=rtpmap:3 GSM/8000
m=video 50286 RTP/AVP 31
a=rtpmap:31 H261/90000
MPDF document that represents the local and the remote session
description:
<session-info>
<context>
<contact>sip:alice@somewhere.example</contact>
<info>session information</info>
</context>
<streams>
<stream>
<media-type>audio</media-type>
<codec><mime-type>audio/PCMU</mime-type></codec>
<codec><mime-type>audio/GSM</mime-type></codec>
<local-host-port>host.somewhere.example:49562</local-host-port>
<remote-host-port>host.anywhere.example:52124</remote-host-port>
</stream>
<stream>
<media-type>video</media-type>
<codec><mime-type>video/H261</mime-type></codec>
<local-host-port>host.somewhere.example:51234</local-host-port>
<remote-host-port>host.anywhere.example:50286</remote-host-port>
</stream>
</streams>
</session-info>
The following MPDF document is a modified version of the above
document, which can be returned by a policy server. This document
reflects a policy that defines a maximum session bandwidth of 192
kbit and a maximum bandwidth for the H261 video stream of 128 kbit.
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<session-info>
<context>
<contact>sip:alice@somewhere.example</contact>
<info>modified session information</info>
</context>
<streams>
<stream label='1'>
<media-type>audio</media-type>
<codec><mime-type>audio/PCMU</mime-type></codec>
<codec><mime-type>audio/GSM</mime-type></codec>
<local-host-port>host.somewhere.example:49562</local-host-port>
<remote-host-port>host.anywhere.example:52124</remote-host-port>
</stream>
<stream label='2'>
<media-type>video</media-type>
<codec><mime-type>video/H261</mime-type></codec>
<local-host-port>host.somewhere.example:51234</local-host-port>
<remote-host-port>host.anywhere.example:50286</remote-host-port>
</stream>
</streams>
<max-stream-bw label='2'>128</max-stream-bw>
<max-session-bw>192</max-session-bw>
</session-info>
9. Relax NG Definition
This section needs to be updated.
<?xml version="1.0"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0"
ns="urn:ietf:params:xml:ns:mediadataset"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<define name="PropertySetExtension" combine="interleave">
<choice>
<element name="session-info">
<ref name="SettingContainerAttributes"/>
<optional>
<ref name="ElementContext"/>
</optional>
<optional>
<ref name="ElementStreams"/>
</optional>
<zeroOrMore>
<ref name="ElementMaxBandwidth"/>
</zeroOrMore>
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<zeroOrMore>
<ref name="ElementMaxSessionBandwidth"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementMaxStreamBandwidth"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementMediaIntermediaries"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementQoSDSCP"/>
</zeroOrMore>
</element>
<element name="session-policy">
<ref name="SettingContainerAttributes"/>
<optional>
<ref name="ElementContext"/>
</optional>
<optional>
<ref name="ElementLocalPorts"/>
</optional>
<zeroOrMore>
<ref name="ElementMediaTypes"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementCodecs"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementMaxBandwidth"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementMaxSessionBandwidth"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementMaxStreamBandwidth"/>
</zeroOrMore>
<zeroOrMore>
<ref name="ElementQoSDSCP"/>
</zeroOrMore>
</element>
</choice>
</define>
<define name="ElementMediaTypes">
<element name="media-types">
<ref name="PolicyGeneralAttributes"/>
<optional>
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<ref name="SettingContainerAttributes"/>
</optional>
<zeroOrMore>
<ref name="ElementMediaType"/>
</zeroOrMore>
</element>
</define>
<define name="ElementMediaType">
<element name="media-type">
<data type="string" />
<optional>
<ref name="AttributeQ"/>
</optional>
<optional>
<ref name="AttributePolicy"/>
</optional>
<optional>
<ref name="AttributeGeneric"/>
</optional>
</element>
</define>
<define name="ElementCodecs">
<element name="codecs">
<ref name="PolicyGeneralAttributes"/>
<optional>
<ref name="SettingContainerAttributes"/>
</optional>
<zeroOrMore>
<ref name="ElementCodec"/>
</zeroOrMore>
</element>
</define>
<define name="ElementCodec">
<element name="codec">
<optional>
<ref name="AttributeQ"/>
</optional>
<optional>
<ref name="AttributePolicy"/>
</optional>
<optional>
<ref name="AttributeGeneric"/>
</optional>
<element name="mime-type">
<data type="string" />
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</element>
<zeroOrMore>
<element name="mime-parameter">
<data type="string" />
</element>
</zeroOrMore>
</element>
</define>
<define name="ElementStreams">
<element name="streams">
<optional>
<ref name="AttributeGeneric"/>
</optional>
<oneOrMore>
<ref name="ElementStream"/>
</oneOrMore>
</element>
</define>
<define name="ElementStream">
<element name="stream">
<optional>
<ref name="AttributeDirection"/>
</optional>
<optional>
<ref name="AttributeLabel"/>
</optional>
<optional>
<ref name="AttributeGeneric"/>
</optional>
<ref name="ElementMediaType"/>
<oneOrMore>
<ref name="ElementCodec"/>
</oneOrMore>
<element name="local-host-port">
<data type="string" />
</element>
<optional>
<element name="remote-host-port">
<data type="string" />
</element>
</optional>
</element>
</define>
<define name="ElementMaxBandwidth">
<element name="max-bw">
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<data type="integer" />
<ref name="PolicyGeneralAttributes"/>
</element>
</define>
<define name="ElementMaxSessionBandwidth">
<element name="max-session-bw">
<data type="integer" />
<ref name="PolicyGeneralAttributes"/>
</element>
</define>
<define name="ElementMaxStreamBandwidth">
<element name="max-stream-bw">
<data type="integer" />
<ref name="PolicyGeneralAttributes"/>
<optional>
<ref name="AttributeMediaType"/>
</optional>
<optional>
<ref name="AttributeLabel"/>
</optional>
</element>
</define>
<define name="ElementMediaIntermediaries">
<element name="media-intermediaries">
<ref name="PolicyGeneralAttributes"/>
<oneOrMore>
<choice>
<element name="fixed-intermediary">
<element name="int-host-port">
<data type="string" />
</element>
<zeroOrMore>
<element name="int-addl-port">
<data type="integer" />
</element>
</zeroOrMore>
</element>
<element name="turn-intermediary">
<element name="int-host-port">
<data type="string" />
</element>
<zeroOrMore>
<element name="int-addl-port">
<data type="integer" />
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</element>
</zeroOrMore>
<zeroOrMore>
<element name="shared-secret">
<data type="string" />
</element>
</zeroOrMore>
</element>
</choice>
</oneOrMore>
</element>
</define>
<define name="ElementQoSDSCP">
<element name="qos-dscp">
<data type="integer" />
<ref name="PolicyGeneralAttributes"/>
<optional>
<ref name="AttributeMediaType"/>
</optional>
</element>
</define>
<define name="ElementLocalPorts">
<element name="local-ports">
<data type="string" />
<interleave>
<optional>
<ref name="AttributeVisibility"/>
</optional>
<optional>
<ref name="AttributeGeneric"/>
</optional>
</interleave>
</element>
</define>
<define name="ElementContext">
<element name="context">
<interleave>
<optional>
<element name="info">
<data type="string" />
</element>
</optional>
<optional>
<element name="domain">
<data type="string" />
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</element>
</optional>
<optional>
<element name="request-URI">
<data type="string" />
</element>
</optional>
<optional>
<element name="token">
<data type="string" />
</element>
</optional>
<zeroOrMore>
<element name="contact">
<data type="string" />
</element>
</zeroOrMore>
</interleave>
</element>
</define>
<define name="PolicyGeneralAttributes">
<optional>
<ref name="AttributeVisibility"/>
</optional>
<optional>
<ref name="AttributeDirection"/>
</optional>
<optional>
<ref name="AttributeGeneric"/>
</optional>
</define>
<define name="AttributeMediaType">
<attribute name="media-type">
<data type="string" />
</attribute>
</define>
<define name="AttributeLabel">
<attribute name="label">
<data type="string" />
</attribute>
</define>
</grammar>
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10. Security Considerations
Session policy information can be sensitive information. The
protocol used to distribute session policy information 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.
11. IANA Considerations
This document registers a new media type, application/
media-policy-dataset+xml, and a new XML namespace.
11.1. Media Type Registration
Media type name: application
Media subtype name: media-policy-dataset+xml
Mandatory parameters: none
Optional parameters: Same as charset parameter application/xml as
specified in RFC 3023 [RFC3023].
Encoding considerations: Same as encoding considerations of
application/xml as specified in RFC 3023 [RFC3023].
Security considerations: See Section 10 of RFC 3023 [RFC3023] and
Section 10 of this specification.
Interoperability considerations: none.
Published specification: This document.
Applications which use this media type: This document type has been
used to convey media policy information between SIP user agents and a
domain.
Additional Information:
Magic Number: None
File Extension: .mpf or .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: Volker Hilt,
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<volkerh@bell-labs.com>
Intended usage: COMMON
Author/Change controller: The IETF.
11.2. URN Sub-Namespace Registration
This section registers a new XML namespace, as per the guidelines in
[RFC3688]
URI: The URI for this namespace is
urn:ietf:params:xml:ns:mediadataset.
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>Media Policy Dataset Namespace</title>
</head>
<body>
<h1>Namespace for Media Policy Datasets</h1>
<h2>urn:ietf:params:xml:ns:mediadataset</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997.
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[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media
Types", RFC 3023, January 2001.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[RFC4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574, August 2006.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, February 2007.
[RFC4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975, September 2007.
[RFC4976] Jennings, C., Mahy, R., and A. Roach, "Relay Extensions
for the Message Sessions Relay Protocol (MSRP)", RFC 4976,
September 2007.
[RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN): Relay Extensions to Session
Traversal Utilities for NAT (STUN)", RFC 5766, April 2010.
[W3C.REC-xml-20040204]
Sperberg-McQueen, C., Maler, E., Yergeau, F., Paoli, J.,
and T. Bray, "Extensible Markup Language (XML) 1.0 (Third
Edition)", World Wide Web Consortium FirstEdition REC-xml-
20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-20040204>.
[W3C.REC-xml-names-19990114]
Hollander, D., Layman, A., and T. Bray, "Namespaces in
XML", World Wide Web Consortium FirstEdition REC-xml-
names-19990114, January 1999,
<http://www.w3.org/TR/1999/REC-xml-names-19990114>.
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12.2. Informative References
[I-D.ietf-sip-session-policy-framework]
Hilt, V., Camarillo, G., and J. Rosenberg, "A Framework
for Session Initiation Protocol (SIP) Session Policies",
draft-ietf-sip-session-policy-framework-08 (work in
progress), December 2010.
[I-D.ietf-sipping-config-framework]
Channabasappa, S., "A Framework for Session Initiation
Protocol User Agent Profile Delivery",
draft-ietf-sipping-config-framework-18 (work in progress),
October 2010.
[RFC2648] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[RFC3261] 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.
[RFC4629] Ott, H., Bormann, C., Sullivan, G., Wenger, S., and R.
Even, "RTP Payload Format for ITU-T Rec", RFC 4629,
January 2007.
[RFC4856] Casner, S., "Media Type Registration of Payload Formats in
the RTP Profile for Audio and Video Conferences",
RFC 4856, February 2007.
Appendix A. Acknowledgements
Many thanks to Allison Mankin, Dan Petrie, Martin Dolly, Adam Roach
and Ben Campbell for the discussions and suggestions. Many thanks to
Roni Even and Mary Barnes for reviewing the draft and to Jari
Urpalainen for helping with the Relax NG schema.
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Authors' Addresses
Volker Hilt
Bell Labs/Alcatel-Lucent
791 Holmdel-Keyport Rd
Holmdel, NJ 07733
USA
Email: volkerh@bell-labs.com
Dale R. Worley
Avaya Inc.
600 Technology Park Dr.
Billerica, MA 01821
US
Email: dworley@avaya.com
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
Jonathan Rosenberg
jdrosen.net
Monmouth, NJ
USA
Email: jdrosen@jdrosen.net
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