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SIMPLE WG M. Lonnfors
Internet-Draft Nokia Research Center
Expires: December 25, 2003 K. Kiss
Nokia
June 26, 2003
Device capability PIDF status extension
draft-lonnfors-simple-prescaps-ext-01
Status of this Memo
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all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on December 25, 2003.
Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
Interoperation of Instant Messaging and Presence systems has been
defined in IMPP Working Group. IMPP WG has come up with baseline
interoperable operations and formats for Presence and Instant
Messaging systems. However, these base formats might need
standardized extensions in order to enable building rational
applications using Presence and Instant Messaging. This memo proposes
an extension to PIDF presence document format to represent SIP Caller
preferences and Callee capabilities features to be used in SIMPLE
based Presence systems but may also be applied to other protocols as
well.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Support for Caller Preferences and Callee Capabilities . . . . 4
3.1 Extension overview . . . . . . . . . . . . . . . . . . . . . . 4
3.2 Handing of Caller Preferences and Callee Capabilities
matching rules . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3 <prescaps> element . . . . . . . . . . . . . . . . . . . . . . 5
3.4 <feature> element . . . . . . . . . . . . . . . . . . . . . . 5
3.5 <value> element . . . . . . . . . . . . . . . . . . . . . . . 6
3.6 Handling of Caller Preferences and Callee Capabilities
priority feature tag . . . . . . . . . . . . . . . . . . . . . 6
4. Guidelines for using extension with PIDF document format . . . 6
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1 Basic extension in tuple level . . . . . . . . . . . . . . . . 7
5.2 Basic extension in status level . . . . . . . . . . . . . . . 7
5.3 Complex example in tuple level . . . . . . . . . . . . . . . . 8
6. XML schema definitions . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7.1 URN sub-namespace registration for
'urn:ietf:params:xml:ns:simple-prescaps-ext' . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
Normative references . . . . . . . . . . . . . . . . . . . . . 11
Informative references . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . 13
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1. Introduction
Interoperation of Instant Messaging and Presence systems has been
defined in IMPP Working Group. Working Group has defined a generic
model for Presence and Instant Messaging [2] and also requirements
for protocols implementing such a system [3]. Common Presence and
Instant Messaging (CPP/CPIM) defines common operations and formats
which all Presence and Instant Messaging services must agree upon so
that basic interoperability would be possible [5], [6]. The actual
base format for presence is being defined in [4]. The PIDF document
format has been designed to reduce the need for gatewaying and to
allow end-to-end security of presence data. It has taken very
minimalistic approach to support such operations. In order to make
the PIDF format usable by different presence applications, these
applications usually must extend the basic PIDF format by standard
XML mechanism as defined in [4].
The aim of this memo is to introduce SIP/SIMPLE specific extension
mechanism for the PIDF document. With this extension SIMPLE based
applications can have richer and usable formats compared to the
baseline PIDF data format. Authors of this document believe that
following items should be included into this extension:
o Support for SIP Caller Preferences and Callee Capabilities [7]
1.1 Motivation
The PIDF document format [4] defines a <contact> element which may
appear once inside every <tuple> element. The content of the
<contact> element encodes the CONTACT ADDRESS and CONTACT MEANS as
defined in [2]. The <contact> element is defined to be an URI. This
URI can be of any URI type. In some implementations this URI can
uniquely identify the application the tuple intends to describe (e.g.
im: URIs). However, this may not be the case in all implementations.
For example in SIP, a SIP URI can represent different kinds of
applications. A SIP URI can be used to contact voice applications,
video applications, or messaging applications. If it is not known by
other means, it might be hard for applications processing the
presence document containing only SIP URI contact addresses to know
what particular application the tuple intends to describe. Also
watchers receiving presence information would probably benefit for
getting more descriptive information about what particular
communication means or applications are supported by the presentity.
Caller Preferences and Callee Capabilities document [7] defines a set
of extensions which allow callers and callees to express preferences
about request handling in SIP servers. The same information could
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provide value also to presence watchers so that they could make more
rational decisions on how presentity should be contacted if presence
document would contain similar information as defined in Caller
Preferences and Callee Capabilities extension. When the Caller
Preferences and Callee Capabilities extension is used in this context
(to represent presence information) there is no need for automated
processing compared to the case when the Caller Preferences and
Callee Capabilities extension is used by proxies or registrars.
Because of this, it should be sufficient to introduce Caller
Preferences and Callee Capabilities extension representation for
presence without specifying similar processing rules as defined in
[7].
1.2 Scope
This document defines extension to the PIDF document format which
enables presence implementations based on SIP protocol to utilize
similar capabilities in presence document as what Caller Preferences
and Callee Capabilities document [7] defines. The intension is only
to allow representation of callee capabilities and not caller
preferences.
This extension does not replace media negotiation mechanisms defined
for SIP (e.g. SDP [11]), therefore media negotiation (e.g. choose
of voice and video codecs) MUST be performed according to [8]. This
extension is only aimed to give the watchers hints about the
presentity's preferences, willingness and capabilities to communicate
before watchers would initiate SIP based communication with the
presentity.
2. Conventions
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] and
indicate requirement levels for compliant implementations.
3. Support for Caller Preferences and Callee Capabilities
This section presents Caller Preferences and Callee Capabilities
extension namespace, its elements, their values, and semantics. This
section also describes how this extension can be further extended.
This extension is intended to be used with application/cpim-pidf+xml
content type and that particular usage is described here. This
extension may also be used with other content types if appropriate.
3.1 Extension overview
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This extension adds most of the features presented in Caller
Preferences and Callee Capabilities document [7] into PIDF presence
document format. Features presented in [7] are added here without
any change in their semantics. Bringing these features to PIDF
presence document format basically means mapping them to XML
structure. However, some Caller Preferences and Callee Capabilities
features are not needed here because identical counterpart already
exists in PIDF. These features are discussed in Section 3.6.
Namespace identifier for this extension is:
urn:ietf:params:xml:ns:simple-prescaps-ext
When this extension namespace is congregated with base PIDF document,
combined document must follow the same general formatting rules as
specified in [4] in chapter 4.1.
3.2 Handing of Caller Preferences and Callee Capabilities matching
rules
Caller Preferences and Callee Capabilities document [7] defines a set
of matching rules which can be used to determine if capabilities
represented by two different URLs are equal. This extension is not
aimed to provide these features i.e. this document does not provide
means to compare two presence documents to determine whether
capabilities represented by those documents match.
3.3 <prescaps> element
Root element of this extension namespace is <prescaps>. The root
element MUST be always present. This element MAY contain one or more
<feature> elements as specified later in this document.
<prescaps> element does not have any attributes and it MAY contain
other namespace declarations for the extensions used in the presence
XML document.
3.4 <feature> element
The <feature> element can represent any feature tag as defined in
Caller Preferences and Callee Capabilities [7] or any media feature
tag registered through [14]. This element MAY appear under <prescaps>
element one or several times. <feature> element has one mandatory
attribute called name. This attribute represents the name of the
feature tag. Each media feature tag (e.g. media, feature and etc.)
SHOULD appear only once inside root element. If media feature tag has
multiple values these values SHOULD be nested inside single <feature>
element. The <feature> cannot be extended using other namespace
declarations.
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3.5 <value> element
The <value> element represents the value of media feature tag. Each
value element SHOULD contain only a single tag value. If <feature>
contains multiple values then all these values should be presented in
different <value> elements. The <value> element has optional
attribute called negated. This attribute is of boolean type. It can
be used to indicate whether feature value is supported or not
supported. Value 'true' indicates that value is not supported and
value 'false' indicates that value is supported. Default value is
'false'. <value> element cannot be extended using other namespace
declarations .
3.6 Handling of Caller Preferences and Callee Capabilities priority
feature tag
PIDF document format allows priority attribute to be used within
<contact> element. Caller Preferences and Callee Capabilities
priority feature tag can be mapped into this attribute and so there
is no need to represent priority feature tag in inside XML structure.
4. Guidelines for using extension with PIDF document format
This section presents guidelines how extension can be used with PIDF
document format.
PIDF format allows use of extension XML namespaces inside <presence>,
<tuple>, and <status> elements. <presence> element is intended to
describe presentity as a whole. Prescaps extension is related to
Contact Address defined by PIDF to which this extension is applied
to. These Contact Addresses can only appear inside <tuple> elements.
The use of this extension in <presence> element level is NOT
RECOMMENDED for this purpose.
It is up to the applications using this extension to decide if they
want to include extension inside <tuple> or inside <status> element.
The semantics of the extension remains same regardless where it is
placed inside PIDF document format. Root element <prescaps> MUST NOT
appear more than once inside a single <tuple> element but can appear
multiple times in PIDF document format inside different <tuple>
elements.
5. Examples
This section presents various examples how this extension can be used
with base PIDF document format.
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5.1 Basic extension in tuple level
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:ext="urn:ietf:params:xml:ns:simple-prescaps-ext"
entity="pres:someone@example.com">
<tuple id="akfjga8v">
<status>
<basic>open</basic>
</status>
<ext:prescaps>
<ext:feature name="Media">
<ext:value>voice</ext:value>
<ext:value>message</ext:value>
</ext:feature>
</ext:prescaps>
<contact>sip:someone@example.com</contact>
</tuple>
</presence>
5.2 Basic extension in status level
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:ext="urn:ietf:params:xml:ns:simple-prescaps-ext"
entity="pres:someone@example.com">
<tuple id="akfjga8v">
<status>
<basic>open</basic>
<ext:prescaps>
<ext:feature name="Media">
<ext:value>voice</ext:value>
<ext:value negated="true">message</ext:value>
</ext:feature>
</ext:prescaps>
</status>
<contact>sip:someone@example.com</contact>
</tuple>
</presence>
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5.3 Complex example in tuple level
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:ext="urn:ietf:params:xml:ns:simple-prescaps-ext"
entity="pres:someone@example.com">
<tuple id="akfjga8v">
<status>
<basic>open</basic>
</status>
<ext:prescaps>
<ext:feature name="Media">
<ext:value>voice</ext:value>
</ext:feature>
<ext:feature name="Mobility">
<ext:value>mobile</ext:value>
</ext:feature>
<ext:feature name="Feature">
<ext:value>voicemail</ext:value>
</ext:feature>
<ext:feature name="Automata">
<ext:value>false</ext:value>
</ext:feature>
<ext:feature name="Class">
<ext:value>business</ext:value>
</ext:feature>
<ext:feature name="Duplex">
<ext:value>full</ext:value>
</ext:feature>
</ext:prescaps>
<contact>sip:someone@example.com</contact>
</tuple>
</presence>
6. XML schema definitions
This section gives the XML Schema Definition for the extension
defined in this document which can be used in the context of
"application/cpim-pidf+xml" content type.
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<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:simple-prescaps-ext"
xmlns:tns="urn:ietf:params:xml:ns:simple-prescaps-ext"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language attribute xml:lang-->
<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:element name="prescaps">
<xs:complexType name="prescaps">
<xs:sequence>
<xs:element name="feature" type="tns:feature" minOccurs="0"
maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</sequence>
</complexType>
<xs:complexType name="feature">
<xs:sequence>
<xs:element name="value" minOccurs="0"
maxOccurs="unbounded"/>
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute name="negated" type="xs:boolean"
use="optional" default="false"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:attribute name="name" type="xs:string" use="required"/>
</sequence>
</complexType>
</schema>
Figure 4
7. IANA Considerations
This memo calls for IANA to register a new XML namespace URN as
defined in [12]
7.1 URN sub-namespace registration for
'urn:ietf:params:xml:ns:simple-prescaps-ext'
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URI:
urn:ietf:params:xml:ns:simple-prescaps-ext
Description:
This is the XML namespace for XML elements defined by [RFCXXXX] to
describe communication means extension for CPIM-PIDF presence
document format in application/cpim-pidf+xml content type.
Registrant Contact:
IETF, SIMPLE working group, <simple@ietf.org>
Mikko Lonnfors, <mikko.lonnfors@nokia.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>SIMPLE PIDF presence capabilities extension</title>
</head>
<body>
<h1>Namespace for SIMPLE presence capabilities extension</h1>
<h2>application/cpim-pidf+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
8. Security Considerations
All security considerations specified in CPIM [5] and in PIDF [4]
documents apply also to this document. For clarity some of the
security considerations are repeated here.
Because presence is very privacy-sensitive information, the transport
protocol for the presence information SHOULD have capabilities to
protect protocol messages from possible threats, such as
eavesdropping, corruption, tamper and replay attacks. The protocols
SHOULD be able to use security mechanisms which are standardized or
being standardized in IETF. However, it depends on the actual
transport protocols which security mechanisms should be used, and it
is beyond the scope of this memo.
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9. Acknowledgements
Authors of this document would like to thank following people for
their contributions and valuable comments: Paul Kyzivat, Markus
Isomaki, and Hisham Khartabil.
Normative references
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Day, M., Rosenberg, J. and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[3] Day, M., Aggarwal, S., Mohr, G. and J. Vincent, "Instant
Messaging / Presence Protocol Requirements", RFC 2779, February
2000.
[4] Sugano, H., Fujimoto, S., Klyne, G. and A. Bateman, "Common
Presence and Instant Messaging (CPIM) Presence Information Data
Format", draft-ietf-impp-cpim-pidf-08, May 2002.
[5] Peterson, J., "Common Profile for Presence (CPP)",
draft-ietf-impp-pres-03, May 2003.
[6] Peterson, J., "Common Profile for Instant Messaging (CPIM)",
draft-ietf-impp-im-03, May 2003.
Informative references
[7] Schulzrinne, H., "Session Initiation Protocol (SIP) Caller
Preferences and Callee Capabilities",
draft-ietf-sip-callerprefs-08, July 2002.
[8] Rosenberg, J., "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[9] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[10] Rosenberg, J., "Session Initiation Protocol (SIP) Extensions
for Presence", draft-ietf-simple-presence-10.txt, May 2002.
[11] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[12] Mealling, M., "The IETF XML Registry",
draft-mealling-iana-xmlns-registry-04, June 2002.
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[13] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) part two: Media Types", RFC 2046, November
1996.
[14] Holtman, K., Mutz, A. and T. Hardie, "Media Feature Tag
Registration Procedure", RFC 2046, March 1999.
Authors' Addresses
Mikko Lonnfors
Nokia Research Center
Itamerenkatu 11-13 00180
Helsinki
Finland
Phone: +358 50 4836402
EMail: mikko.lonnfors@nokia.com
Krisztian Kiss
Nokia
P.O BOX 100
33721 Tampere
Finland
Phone: +358 50 4835363
EMail: krisztian.kiss@nokia.com
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