SIMPLE WG M. Lonnfors
Internet-Draft E. Leppanen
Expires: October 19, 2004 H. Khartabil
Nokia
April 20, 2004
Presence Information Data format (PIDF) Extension for Partial
Presence
draft-ietf-simple-partial-pidf-format-01
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The presence Information Document Format (PIDF) specifies the
baseline XML based format for describing presence information. One of
the characteristic of the PIDF is that document always needs to carry
all presence information available for the presentity. In some
environments where low bandwidth and high latency links can exist it
is often beneficial to limit the amount of information that is
transported over the network. This document introduces a new MIME
type which enables transporting of only changed parts of the PIDF
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based presence information.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Structure of partial PIDF documents . . . . . . . . . . . . . 4
3.1 "version" attribute . . . . . . . . . . . . . . . . . . . 4
3.2 "state" attribute . . . . . . . . . . . . . . . . . . . . 4
3.3 <removed> element . . . . . . . . . . . . . . . . . . . . 5
3.3.1 <t_id> element . . . . . . . . . . . . . . . . . . . . 5
4. Usage of 'application/pidf-partial+xml' . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1 Content-type registration for
'application/pidf-partial+xml' . . . . . . . . . . . . . . 6
5.2 URN sub-namespace registration for
'urn:ietf:params:xml:ns:pidf-partial' . . . . . . . . . . 7
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Interoperability Considerations . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
11.1 Normative references . . . . . . . . . . . . . . . . . . . . 12
11.2 Informative references . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . 14
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1. Introduction
The presence Information Document Format (PIDF) specifies the
baseline XML based format for describing presence information. One of
the characteristic of the PIDF is that document always needs to carry
all presence information available for the presentity. In some
environments where low bandwidth and high latency links can exist it
is often beneficial to limit the amount of information that is
transported over the network. This document introduces a new MIME
type which enables transporting of only changed parts of the PIDF
based presence information.
This new MIME type works at the <tuple> element level so that it
allows indicating if new tuples have been added, previously received
tuples have changed, or that some tuples have been removed. These
modifications are always relative to previously received presence
information.
This document introduces a new MIME-Type 'application/
pidf-partial+xml' which is based on the PIDF presence data format [4]
but is enhanced to support partial presence documents.
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.
This memo makes use of the vocabulary defined in RFC2778 [2]. In
addition, the following terms are defined:
Full presence document: A presence document that contains all the
presentity's presence information that is available to a
particular watcher. A full presence document can be encoded
according to the MIME type 'application/pidf+xml' or, if the
"state" attribute is set to "full", it can also be encoded
according to the MIME type 'application/pidf-partial+xml'.
Partial presence document: A presence document that represents a
fragment of the full presence document. A partial presence
documents can only be understood in the context of the full
presence document, i.e., a partial presence document modifies a
local copy of the full presence document. The MIME type
'application/pidf-partial+xml" document represent a partial
presence document when the "state" attribute is set to "partial".
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3. Structure of partial PIDF documents
The mechanism for implementing the partial PIDF requires defining a
new MIME type. The new MIME type is named as 'application/
pidf-partial+xml'. It is similar to the 'application/pidf+xml' [4]
except that it adds new XML attributes to the <presence> element in
order to enable the partial PIDF. These new XML attributes are
"version" and "state". The new MIME type also introduces a new XML
"removed" element.
Implementations using this document format must follow guidelines
specified in the CPIM presence information data format [4] i.e. the
XML document MUST be well formed and SHOULD be valid. Presence
documents MUST be based on XML 1.0 and MUST be encoded using UTF-8.
This specification makes use of XML namespaces for identifying
presence documents and document fragments. The namespace URI for
elements defined by this specification is a URN [5], using the
namespace identifier 'ietf' specified in RFC 2648 [6] and extended by
RFC3688 [7]. This URN is:
urn:ietf:params:xml:ns:pidf-partial
3.1 "version" attribute
Every presence document compliant with this specification MUST
include the "version" attribute in <presence> element.
The "version" attribute contains a sequence number that is
progressively incremented between subsequent documents i.e. a more
recent document has higher "version" value than a previous one. The
recipient of the document can use "version" attribute to properly
order received documents. The version starts with value 0, and is
incremented by one for each new document. Implementations MUST
support a 32 bit integer in the version number.
3.2 "state" attribute
Every presence document compliant with this specification MUST
include a "state" attribute in the <presence> element. the "state"
attribute can be set to values: 'full' or 'partial'.
The "state" attribute indicates the nature of the presence
information included in the document, i.e., whether it contains a
full or a partial state corresponding to the cases when the full
presence information or only changed parts of the presence
information are delivered. The use of these attributes is similar to
the watcher information template package [8].
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3.3 <removed> element
This element is used to carry a list of tuples that are no longer
present in the presence document. The <removed> element may contain
any number of <t_id> elements, each of which has the value of the
"id" attribute of the tuple which has been removed. The <removed>
element has only semantics for partial presence documents, thus, the
<removed> element MUST NOT be included if "state" attribute has value
"full".
3.3.1 <t_id> element
If a presence document contains a <removed> element, then it MUST
contain at least one <t_id> element. This element contains the tuple
ID as indicated by the "id" attribute of the tuple that has been
removed.
4. Usage of 'application/pidf-partial+xml'
Presence documents which are compliant with the 'application/
pidf-partial+xml' MIME type MUST be constructed according to
following logic:
o All tuple ids used in the presence document MUST be unique within
a document. This means tuple ids both in <tuple> elements and in
<t_id> elements.
o If the presence document represents the full presence state the
"state" attribute MUST be set to "full" and the "version"
attribute MUST be set to the value 0. The rest of the presence
document is constructed as defined in the PIDF [4]. A presence
document that contains a full presence state MUST not contain
<removed> element.
o If the presence document represents a partial presence state the
"state" attribute MUST be set to "partial". The presence document
SHOULD only contain those tuples that have changed compared to
last time the presence document was delivered, i.e., the presence
document contains new, modified, and removed tuples. Once a tuple
is included in the presence document, the whole tuple including
all the child elements and attributes MUST be included.
Implementations MUST NOT include a partial tuple. Tuples which
have not changed SHOULD NOT be included. If some tuples have been
removed "id" attributes of those tuples MUST be listed using
<t_id> elements under <removed> element.
Within the scope of this document tuples are considered to be atomic
data elements. This means that if a presence document contains an
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update to an existing tuple, the whole new tuple replaces the old
one. Partial presence documents can only indicate changes in tuples
(a tuple is new, modified, removed), since this are the only elements
that contains identities to refer to. Other child elements to the
<presence> element defined in the PIDF [4] or in its extensions MUST
always be included in partial presence document with its updated
value, unless the element is removed from the presence information.
5. IANA Considerations
This memo calls for IANA to:
o register a new XML namespace URN per [7].
o register new a content type 'application/pidf-partial+xml' per
RFC2048 [11].
5.1 Content-type registration for 'application/pidf-partial+xml'
MIME media type name: application
MIME subtype name: pidf-partial+xml
Mandatory parameters: none
Optional parameters: charset
Indicates the character encoding of enclosed XML. Default is
UTF-8.
Encoding considerations:
Uses XML, which can employ 8-bit characters, depending on the
character encoding used. See RFC 3023 [9], section 3.2.
Security considerations:
This content type is designed to carry presence data, which may be
considered private information. Appropriate precautions should be
adopted to limit disclosure of this information. Please refer to
[[[RFCXXXX]]] security considerations section for more
information.
Interoperability considerations: none
Published specification: [[[RFCXXXX]]] this document
Applications which use this media type: SIP-based presence systems
Additional information:
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Magic Number: None
File Extension: .xml
Macintosh file type code: "TEXT"
Personal and email address for further information: Mikko
Lonnfors, mikko.lonnfors@nokia.com
Intended usage: LIMITED USE
Author/Change controller:
This specification is a work item of the IETF SIMPLE working
group, with mailing list address <simple@ietf.org>.
5.2 URN sub-namespace registration for
'urn:ietf:params:xml:ns:pidf-partial'
URI:
urn:ietf:params:xml:ns:pidf-partial
Description:
This is the XML namespace for XML elements defined by
[[[RFCXXXX]]] to describe the 'application/pidf-partial+xml'
content type for partial PIDF.
Registrant Contact:
IETF, SIMPLE working group, <simple@ietf.org>
Mikko Lonnfors, <mikko.lonnfors@nokia.com>
XML:
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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>PIDF extension for partial PIDF</title>
</head>
<body>
<h1>Namespace for PIDF extension for partial
notifications</h1>
<h2>application/pidf-partial+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">
RFCXXXX</a>.</p>
</body>
</html>
END
6. Examples
An 'application/pidf-partial+xml' document that contains full state
information:
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<?xml version="1.0" encoding="UTF-8"?>
<pidf-part:presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:pidf-part="urn:ietf:params:xml:ns:pidf-partial"
entity="pres:someone@example.com" version="0"
state="full">
<tuple id="sg89ae">
<status><basic>open</basic>
</status>
<contact priority="0.8">tel:09012345678
</contact>
</tuple>
<tuple id="cg231jcr">
<status><basic>open</basic>
</status>
<contact priority="1.0">
im:pep@example.com</contact>
</tuple>
<tuple id="r1230d">
<status><basic>closed</basic>
</status>
<contact priority="0.9">
sip:pep@example.com</contact>
</tuple>
<note xml:lang="en">
Full state presence document
</note>
</pidf-part:presence>
An updated 'application/pidf-partial+xml' document that contains
partial state information:
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<?xml version="1.0" encoding="UTF-8"?>
<pidf-part:presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:pidf-part="urn:ietf:params:xml:ns:pidf-partial"
entity="pres:someone@example.com" version="1"
state="partial">
<tuple id="cg231jcr">
<status><basic>closed</basic>
</status>
<contact priority="1.0">
im:pep@example.com</contact>
<note xml:lang="en">This is an update of existing
tuple sent in previous notification</note>
</tuple>
<tuple id="wsqw798jcr">
<status><basic>open</basic>
</status>
<contact priority="0.4">
im:mac@hut.com</contact>
<note xml:lang="en">This is a completely new
tuple not sent in previous notification</note>
</tuple>
<note xml:lang="en">
Partial state presence document
</note>
<pidf-part:removed><pidf-part:t_id>r1230d</pidf-part:t_id>
</pidf-part:removed>
</pidf-part:presence>
7. XML Schema
The XML schema for the 'application/pidf-partial+xml' data format.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:pidf-partial"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:pidf="urn:ietf:params:xml:ns:pidf"
xmlns:tns="urn:ietf:params:xml:ns:pidf-partial"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language attribute
xml:lang-->
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<xs:import namespace="http://www.w3.org/XML/1998/namespace"
schemaLocation="http://www.w3.org/2001/xml.xsd"/>
<xs:import namespace="urn:ietf:params:xml:ns:pidf"/>
<xs:element name="presence"
type="tns:partial-presence"/>
<xs:complexType name="partial-presence">
<xs:complexContent>
<xs:extension base="pidf:presence">
<xs:sequence>
<xs:element name="removed"
type="tns:removed_tuple"
minOccurs="0"/>
</xs:sequence>
<xs:attribute name="version"
type="xs:nonNegativeInteger"
use="required"/>
<xs:attribute name="state" use="required">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="full"/>
<xs:enumeration value="partial"/>
</xs:restriction>
</xs:simpleType>
</xs:attribute>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="removed_tuple">
<xs:sequence>
<xs:element name="t_id"
type="xs:ID"
minOccurs="1"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:schema>
8. Interoperability Considerations
This specification is not by default compliant with work done in IMPP
working group. This means that other systems compliant with CPP [10]
will not be by default able to use this specification. However, this
will not cause any interoperability problems because all endpoints
and gateways must support the default MIME type (application/
pidf+xml) regardless if they support this specification. Thus if a
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gateway or another end point does not understand this specification
it will not be used.
Other CPP compliant (other than SIP based) systems can also support
this specification if they have a mechanism to indicate support for
it. If they do it is possible to build a gateway which will preserves
the end to end integrity with usage of partial PIDF.
9. Security Considerations
Presence information may contain highly sensitive information about
the presentities. The protocol used to distribute it SHOULD ensure
privacy, message integrity and authentication. Furthermore, the
protocol should provide access controls which restrict who can see
who else's presence information. All security considerations
identified for PIDF [4] apply unchanged for this document.
10. Acknowledgements
The authors would like to thank Jose Costa-Requena, Jyrki Aarnos,
Jonathan Rosenberg, Dean Willis, Miguel Garcia, Kriztian Kiss, Ben
Cambell, and Anders kristenssen for their valuable comments and
contributions.
11. References
11.1 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] Rosenberg, J., "SIP Extensions for Presence",
draft-ietf-simple-presence-10 (work in progress), January 2003.
[4] Sugano, H., "CPIM presence information data format",
draft-ietf-impp-cpim-pidf-08 (work in progress), May 2003.
[5] Moats, R., "URN syntax", RFC 2141, May 1997.
[6] Moats, R., "A URN namespace for IETF documents", RFC 2648, Aug.
1999.
11.2 Informative references
[7] Mealling, M., "The IETF XML Registry", RFC 3688, BCP 81,
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January 2004.
[8] Rosenberg, J., "A Watcher Information Event Template-Package
for the Session Initiation Protocol (SIP)",
draft-ietf-simple-winfo-package-05 (work in progress), January
2003.
[9] Murata, M., "XML media types", RFC 3023, January 2001.
[10] Crocker, D. and J. Peterson, "Common Profile for Presence
(CPP)", draft-ietf-impp-pres-02.txt (work in progress).
[11] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet
Mail Extensions (MIME) Part Four: Registration Procedures", RFC
2048, November 1996.
Authors' Addresses
Mikko Lonnfors
Nokia
Itamerenkatu 11-13 00180
Helsinki
Finland
Phone: +358 71 8008000
EMail: mikko.lonnfors@nokia.com
Eva Leppanen
Nokia
P.O BOX 785
Tampere
Finland
Phone: +358 7180 77066
EMail: eva-maria.leppanen@nokia.com
Hisham Khartabil
Nokia
P.O. Box 321
Helsinki
Finland
Phone: +358 7180 76161
EMail: hisham.khartabil@nokia.com
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