SIPPING Working Group G. Camarillo
Internet-Draft Ericsson
Expires: March 1, 2004 September 2003
A Session Initiation Protocol (SIP) Event Package for Media Policy
draft-camarillo-sipping-policy-package-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document defines a SIP event package for session policies. User
agents can subscribe to this event package to obtain information
about the session policy of a domain (e.g., allowed and disallowed
codecs or maximum bandwidth).
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Package Definition . . . . . . . . . . . . . . . . . . . . . 3
3.1 Event Package Name . . . . . . . . . . . . . . . . . . . . . 3
3.2 Event Package Parameters . . . . . . . . . . . . . . . . . . 4
3.3 SUBSCRIBE Bodies . . . . . . . . . . . . . . . . . . . . . . 4
3.4 Subscription Duration . . . . . . . . . . . . . . . . . . . 4
3.5 NOTIFY Bodies . . . . . . . . . . . . . . . . . . . . . . . 4
3.6 Notifier Processing of SUBSCRIBE Requests . . . . . . . . . 4
3.7 Notifier Generation of NOTIFY Requests . . . . . . . . . . . 4
3.8 Subscriber Processing of NOTIFY Requests . . . . . . . . . . 5
3.9 Handling of Forked Request . . . . . . . . . . . . . . . . . 5
3.10 Rate of Notifications . . . . . . . . . . . . . . . . . . . 5
3.11 State Agents . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Session Policy Information Format . . . . . . . . . . . . . 5
5. Structure of the Session Policy Information . . . . . . . . 5
6. Protocols Element . . . . . . . . . . . . . . . . . . . . . 6
6.1 Methods Element . . . . . . . . . . . . . . . . . . . . . . 6
6.2 Option-tags Element . . . . . . . . . . . . . . . . . . . . 6
6.3 Feature-tags Element . . . . . . . . . . . . . . . . . . . . 6
6.4 Bodies Element . . . . . . . . . . . . . . . . . . . . . . . 7
6.5 Extensibility . . . . . . . . . . . . . . . . . . . . . . . 7
6.6 Example of a Protocol Element . . . . . . . . . . . . . . . 7
7. Media Element . . . . . . . . . . . . . . . . . . . . . . . 8
7.1 Stream Element . . . . . . . . . . . . . . . . . . . . . . . 8
7.1.1 Codecs Element . . . . . . . . . . . . . . . . . . . . . . . 8
7.1.2 Transports Element . . . . . . . . . . . . . . . . . . . . . 8
7.1.3 Directions Element . . . . . . . . . . . . . . . . . . . . . 9
7.1.4 Extensibility . . . . . . . . . . . . . . . . . . . . . . . 9
7.2 Example of a Media Element . . . . . . . . . . . . . . . . . 9
8. Schema . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
9. Example . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Security Considerations . . . . . . . . . . . . . . . . . . 10
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 10
11.1 MIME Registration for application/session-policy+xml . . . . 10
11.2 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:sessionpolicy . . . . . . . . . . . . 11
Normative References . . . . . . . . . . . . . . . . . . . . 12
Informational References . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . 13
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1. Introduction
Some domains have certain policies regarding the types of sessions
users can establish. These policies are typically enforced somehow.
For example, if the policy of a domain disallows the use of a
particular codec, access routers will discard packets that transport
media encoded with that codec. Unfortunatelly, enforcement mechanisms
do not usually inform the user about what is happening. They silently
keep the user from doing anything against the policy.
Therefore, users need a means to obtain the policy of their domain in
order not to try anything against it. Users also need to be informed
about changes in this policy, since the session policy of a domain is
a dynamic piece of information (e.g., high-bandwidth codecs are
disallowed only in presence of a high number of users).
Other domains have policies regarding the type of user agents that
can use their network. For example, a domain could require that user
agents using its network use a particular protocol (e.g., SIP) with a
set of extensions (e.g., preconditions must be used). A user agent
needs to know the exact policy of a domain in order to be able to use
the right configuration to send and receive traffic in that domain.
We define a SIP event package that allows a user agent to subscribe
to the session policy information of a domain.
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, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
3. Package Definition
This section fills in the details needed to specify an event package
as defined in Section 4.4 of RFC 3265 [2].
3.1 Event Package Name
The name of this package is "session-policy". As specified in RFC
3265 [2], this value appears in the Event header field present in
SUBSCRIBE and NOTIFY requests.
Event: session-policy
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3.2 Event Package Parameters
No package specific Event header field parameters are defined for
this event package.
3.3 SUBSCRIBE Bodies
A SUBSCRIBE for session policy events MAY contain a body. This body
would serve the purpose of filtering the subscription. The definition
of such a body is outside the scope of this specification.
A SUBSCRIBE for the session policy package MAY be sent without a
body. This implies that the default session policy filtering policy
has been requested. The default policy is that notifications are
generated every time there is any change in the media policy for the
user.
3.4 Subscription Duration
The default expiration of subscriptions to session policy state is
one hour (3600 seconds).
3.5 NOTIFY Bodies
In this event package, the body of the notification contains a
session policy document. This document describes the session policy
of a domain for a user. All subscribers and notifiers MUST support
the "application/session-policy+xml" data format described in Section
4. The subscribe request MAY contain an Accept header field. If no
such header field is present, it has a default value of "application/
session-policy+xml". If the header field is present, it MUST include
"application/session-policy+xml", and MAY include any other types
capable of representing session policy state.
3.6 Notifier Processing of SUBSCRIBE Requests
Session policy state can be sensitive information. Therefore, all
subscriptions to it SHOULD be authenticated and authorized before
approval. Authentication MAY be performed using any of the techniques
available through SIP, including digest, S/MIME, TLS or other
transport specific mechanisms. It is RECOMMENDED that a user be
allowed to subscribe to their own session policy.
3.7 Notifier Generation of NOTIFY Requests
Notifications SHOULD be generated for the session policy package
whenever there is a change in the session policy for the user.
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3.8 Subscriber Processing of NOTIFY Requests
NOTIFY requests contain the full session policy state. The subscriber
does not need to perform any type of information aggregation.
3.9 Handling of Forked Request
Session policy state is normally stored in some repository.
Therefore, there is usually a single place where the session policy
for a user is resident. This implies that a subscription for this
information is readily handled by a single element with access to
this repository. There is, therefore, no compelling need for a
subscription to session policy information to fork. As a result, a
subscriber MUST NOT create multiple dialogs as a result of a single
subscription request. The required processing to guarantee that only
a single dialog is established is described in Section 4.4.9 of RFC
3265 [2].
3.10 Rate of Notifications
For reasons of congestion control, it is important that the rate of
notifications not become excessive. As a result, it is RECOMMENDED
that the server not generate notifications for a single subscriber at
a rate faster than once every 5 seconds.
3.11 State Agents
State agents have no role in the handling of this package.
4. Session Policy Information Format
Session policy information information is an XML document that MUST
be well-formed and SHOULD be valid. Session policy documents MUST be
based on XML 1.0 and MUST be encoded using UTF-8. This specification
makes use of XML namespaces for identifying session policy documents.
The namespace URI for elements defined by this specification is a URN
[3], using the namespace identifier 'ietf' defined by RFC 2648 [4]
and extended by [6]. This URN is:
urn:ietf:params:xml:ns:sessionpolicy
A session policy document begins with the root element tag
"sessionpolicy".
5. Structure of the Session Policy Information
A session policy document starts with a sessionpolicy element. This
element has three mandatory attributes:
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version: This attribute allows the recipient of session policy
information documents to properly order them. Versions start at 0,
and increment by one for each new document sent to a subscriber.
Versions are scoped within a subscription. Versions MUST be
representable using a 32 bit integer.
domain: This attribute contains the domain the policy belongs to.
entity: This attribute contains a URI that identifies the user
whose media policy information is reported in the remainder of the
document.
The sessionpolicy element has a series of sessionpolicy sub-elements:
zero or one protocols element and zero or one media element.
6. Protocols Element
The protocols element contains a series of protocol sub-elements.
Each protocol sub-element contains the policy related to the usage of
a particular protocol.
The protocol element has a single mandatory attribute, name. The name
attribute identifies a protocol the policy of each protocol element
is referring to. The protocol element has a series of sub-elements:
methods, option-tags, feature-tags, and bodies.
6.1 Methods Element
The methods element contains a default-policy attribute and method
elements. The default-policy attribute contains the policy for
methods that are not listed as method elements. A method element has
two attributes: name and policy. The name attribute identifies a
method, and the policy attribute contains the policy for that method
(allowed or disallowed).
6.2 Option-tags Element
The option-tags element contains a default-policy attribute and
option-tag elements. The default-policy attribute contains the policy
for option-tags that are not listed as option-tag elements. An
option-tag element has two attributes: name and policy. The name
attribute identifies a method, and the policy attribute contains the
policy for that method (mandatory, allowed, or disallowed).
6.3 Feature-tags Element
The feature-tags element contains a default-policy attribute and
feature-tag elements. The default-policy attribute contains the
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policy for feature-tags that are not listed as feature-tag elements.
An feature-tag element has two attributes: name and policy. The name
attribute identifies a method, and the policy attribute contains the
policy for that method (allowed, or disallowed).
6.4 Bodies Element
The bodies element contains a default-policy attribute, a
default-encryption attribute and body-disposition elements. The
default-policy attribute contains the policy for body dispositions
that are not listed as body-disposition elements. The
default-encryption attribute contains the encryption policy for body
dispositions that are not listed as body-disposition elements.
A body-disposition element can have a number of attributes: name,
policy, default-policy, and encryption. The name attribute identifies
a body-disposition, and the policy attribute contains the policy for
that body-disposition (allowed, or disallowed). The default-policy
attribute contains the policy for body formats that are not listed as
body-format elements. The encryption attribute indicates whether or
not encryption is allowed for a particular body disposition.
A body-disposition element contains body-format elements. A
body-format element can have a two attributes: name and policy. The
name attribute identifies a body-format, and the policy attribute
contains the policy for that body-format (allowed or disallowed).
6.5 Extensibility
Other elements from different namespaces MAY be present within a
protocol element for the purposes of extensibility; elements or
attributes from unknown namespaces MUST be ignored.
6.6 Example of a Protocol Element
<protocols>
<protocol name="SIP">
<methods default-policy="allowed">
<method name="MESSAGE" policy="disallowed"/>
</methods>
<option-tags default-policy="disallowed">
<option-tag name="100rel" policy="mandatory"/>
<option-tag name="preconditions" policy="allowed"/>
</option-tags>
<feature-tags default-policy="disallowed">
<feature-tag name="video" policy="allowed"/>
</feature-tags>
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<bodies default-policy="allowed" default-encryption="allowed">
<body-disposition name="session" policy="allowed"
encryption="disallowed" default-policy="disallowed">
<body-format name="application/sdp" policy="allowed"/>
</body-disposition>
</bodies>
</protocol>
</protocols>
7. Media Element
The media element contains the policy related to the characteristics
of media streams of different types. It has three attributes:
maxbandwidth, maxnostreams, and default-policy. They contain the
maximum bandwidth the user can count on, the maximum number of media
streams that the user is allowed to established at the same time, and
the default policy (allowed or disallowed) for stream types that are
not listed as stream elements.
The media element contains a series of stream elements.
7.1 Stream Element
A stream element can have a number of attributes: type, policy,
maxbandwidth, and maxnostreams. The type attribute identifies a media
type, and the policy attribute contains the policy for that media
type (allowed or disallowed).
The stream element has a number of optional sub-element: the codecs
element, the transports element and the directions element.
7.1.1 Codecs Element
The codecs element contains a default-policy attribute and codec
elements. The default-policy attribute contains the policy for codecs
that are not listed as codec elements. A codec element can have two
attributes: name and policy. The name attribute identifies a codec,
and the policy attribute contains the policy for that codec (allowed,
or disallowed).
7.1.2 Transports Element
The transports element contains a default-policy attribute and
transport elements. The default-policy attribute contains the policy
for transports that are not listed as transport elements. A tranport
element can have two attributes: name and policy. The name attribute
identifies a transport, and the policy attribute contains the policy
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for that tranport (allowed, or disallowed).
7.1.3 Directions Element
The directions element contains a default-policy attribute and
direction elements. The default-policy attribute contains the policy
for directions that are not listed as direction elements. A direction
element can have two attributes: name and policy. The name attribute
identifies a direction (sendrecv, sendonly, recvonly), and the policy
attribute contains the policy for that direction (allowed, or
disallowed).
7.1.4 Extensibility
Other elements from different namespaces MAY be present within a
stream element for the purposes of extensibility; elements or
attributes from unknown namespaces MUST be ignored.
7.2 Example of a Media Element
<media maxnostreams="4" default-policy="disallowed">
<stream type="audio" policy="allowed">
<codecs default-policy="allowed">
<codec name="PCMU" policy="disallowed"/>
<codec name="PCMA" policy="disallowed"/>
</codecs>
<transports default-policy="disallowed">
<transport name="RTP/AVP" policy="allowed"/>
</transports>
<directions default-policy="disallowed">
<direction name="sendonly" policy="allowed"/>
</directions>
</stream>
</media>
8. Schema
The following is the schema for the application/session-policy+xml
type:
<?xml version="1.0" encoding="UTF-8"?>
TBD
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9. Example
The following is is an example of an application/session-policy+xml
document:
<?xml version="1.0" encoding="UTF-8"?>
<sessionpolicy xmlns="urn:ietf:params:xml:ns:sessionpolicy"
version="0"
domain="example.com"
entity="sip:alice@example.com">
<protocols>
<protocol name="SIP">
<methods default-policy="allowed"/>
<option-tags default-policy="allowed"/>
<feature-tags default-policy="allowed"/>
<bodies default-policy="allowed" default-encryption="allowed"/>
</protocol>
</protocols>
<media default-policy="allowed"/>
</sessionpolicy>
10. Security Considerations
Session policy information can be sensitive information. The protocol
used to distribute it SHOULD ensure privacy, message integrity and
authentication. Furthermore, the protcol SHOULD provide access
controls which restrict who can see who elses session policy
information.
11. IANA Considerations
This document registers a new MIME type, application/
session-policy+xml, and registers a new XML namespace.
11.1 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 [5].
Encoding considerations: Same as encoding considerations of
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application/xml as specified in RFC 3023 [5].
Security considerations: See Section 10 of RFC 3023 [5] 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 download the session policy of a domain to SIP user agents.
Additional Information:
Magic Number: None
File Extension: .wif or .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: Gonzalo
Camarillo, <Gonzalo.Camarillo@ericsson.com>
Intended usage: COMMON
Author/Change controller: The IETF.
11.2 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>,
Gonzalo Camarillo, <Gonzalo.Camarillo@ericsson.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>
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<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>application/session-policy+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[3] Moats, R., "URN Syntax", RFC 2141, May 1997.
[4] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[5] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[6] Mealling, M., "The IETF XML Registry",
draft-mealling-iana-xmlns-registry-05 (work in progress), June
2003.
Informational References
Author's Address
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
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