SIMPLE WG M. Lonnfors
Internet-Draft Nokia Research Center
Expires: November 5, 2003 E. Leppanen
H. Khartabil
Nokia
May 7, 2003
BINPIDF - External Object Extension to Presence Information Data
Format
draft-lonnfors-simple-binpidf-01
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This memo specifies a methodology whereby external content to a
presence information document can be referenced in XML encoded
presence information document (PIDF). The external content can be
either transferred directly in the payload of messages or indirectly
as an HTTP reference. The external part might contain binary data
such as images.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Methodology . . . . . . . . . . . . . . . . . . . 3
4. BINPIDF Elements . . . . . . . . . . . . . . . . . . . . . . . 4
4.1 Namespace . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2 'ObjLink' Element . . . . . . . . . . . . . . . . . . . . . . 4
5. How To Utilize this Specification . . . . . . . . . . . . . . 4
5.1 Direct Link to External Content . . . . . . . . . . . . . . . 4
5.2 Reference to Multipart where External Object is Embedded . . . 5
5.3 Reference to Multipart where Link and Another Information
about the External Object is Found . . . . . . . . . . . . . . 5
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1 Binary Objects both Directly Embedded and Indirectly
Referenced in Multiparts . . . . . . . . . . . . . . . . . . . 5
6.2 External Content Reference in Presence Information without
MIME Multipart Definition . . . . . . . . . . . . . . . . . . 7
7. XML Schema Definition . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
10. Changes from the Version 00 . . . . . . . . . . . . . . . . . 8
References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . 11
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1. Introduction
The Presence Information Data Format (PIDF) is described in [2]. It
defines a generic XML encoded format to express a presentity's
presence information. However, it does not specify any mechanism how
external objects, e.g. pictures, as a part of presence information
can be represented in such XML documents.
The Content Indirection document [4] provides an extension to the URL
MIME External-Body Access-Type [8] to allow any MIME part in a SIP
message to be referred indirectly via a URL. In addition there is a
need to specify an extension to PIDF in order to use the Content
Indirection mechanism for the Presence in a way that the XML encoded
presence information is carried directly in MIME message while
external objects are referenced indirectly.
Using the SIP Events [5] as transport for PIDF documents it is
equally feasible to deliver the external objects in the payload of a
SIP message, namely SIP NOTIFY. The MIME Multipart/Related content
type [6] provides a tool for placing a reference to an external
content as a MIME multipart. An extension to PIDF is needed for
referencing the multiparts from a PIDF formatted presence information
document. A similar kind of approach of utilizing the MIME Multipart/
Related with HTML can be found in [7].
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. Overview of Methodology
This section provides an overview for having references to the
external objects (direct and indirect content) in presence
information.
The external object can be embedded as one part of a multipart
payload of a MIME message, can be stored at an external location
where the multipart payload includes a URL to external object using
Content Indirection [4], or the PIDF XML part can directly contain a
URL link to the content. The MIME Multipart/Related content type [6]
is used for direct delivery of the external object.
The presence information data format is extended with an object link
(ObjLink) XML element. Each separate external content has its own
ObjLink value within presence information. The value of the ObjLink
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is URL (see more information about the syntax of URL from [9]). The
value might be either the Content ID of the external object part in
the multipart payload or a URL to the location of the external
content. The application processing the PIDF document is able to
discover the location of the content from the scheme of the URL (see
more information about the reserved scheme names from [9] and [10]).
The 'cid:' scheme [10] refers to a specific body part of a message.
4. BINPIDF Elements
4.1 Namespace
The namespace declaration to the PIDF extension specified in this
document is 'urn:ietf:params:xml:ns:pidf-ext-cont'.
4.2 'ObjLink' Element
The 'ObjLink' XML element contains a URL reference [9] to the
external object. The scheme of the URL specifies how the value of the
ObjLink element is processed. The value of the ObjLink might
correspond to the Content ID [10] parameter of the multipart made
according to MIME Multipart/Related content type [6], or to the
'external' location of the content.
The ObjLink element MAY have a ContentType attribute. The ContentType
should be used when the URL references directly to an external
location. The value of the attribute describes the content (see
description of entity headers from [11]).
5. How To Utilize this Specification
This chapter describes how the payload of a SIP message is composed
when there is a need to convey external objects to XML encoded
presence information document between the client and presence server.
The following methods for delivering the external object are
explained later in their own subchapters: a direct link to the
external content within a PIDF based XML document and a reference to
a multipart having either the content of the external object embedded
or a URL (and other information) to an external location where the
content is stored.
5.1 Direct Link to External Content
The ObjLink XML element is included in PIDF to point to the location
where the external content is stored. The used content type in the
SIP message is one of the normal content type(s) of presence service.
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5.2 Reference to Multipart where External Object is Embedded
The content type of the SIP message and the multiparts of the payload
are composed according to [6] (MIME Multipart/Related). The XML
encoded presence information in PIDF is the 'root' of the body part.
The ObjLink XML element is used within presence information in PIDF
to reference to the multipart where the content of the external
object is found.
5.3 Reference to Multipart where Link and Another Information about the
External Object is Found
The content type of the SIP message and the multiparts of the payload
are composed according to [6] (MIME Multipart/Related). The XML
encoded presence information in PIDF is the 'root' of the body part.
The ObjLink XML element is used within presence information in PIDF
to reference the part in the multipart payload where the additional
information (e.g., URL) of the external object is found. The
multipart of the external object is composed according to [4].
6. Examples
6.1 Binary Objects both Directly Embedded and Indirectly Referenced in
Multiparts
Presence information subscription from client to server:
SUBSCRIBE sip:john@pres.example.com SIP/2.0
Via: SIP/2.0/TCP xxxxx;branch=z9hG4bKwYb6QREiCL
Max-Forwards: 70
To: <sip:john@pres.example.com>
From: <sip:adam@example.com>;tag=ie4hbb8t
Call-ID: cdB34qLToC@terminal.example.com
CSeq: 322723822 SUBSCRIBE
Contact: xxxx
Event: presence
Expires: 7200
Accept: application/cpim-pidf+xml
Accept: multipart/related
Accept: message/external-body, text/html, text/plain, image/*
Content-Length: 0
(200 OK are omitted)
The NOTIFY looks like:
NOTIFY sip:terminal.example.com SIP/2.0
Via: SIP/2.0/TCP pres.example.com;branch=z9hG4bKMgRenTETmm
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Max-Forwards: 70
From: <sip:john@pres.example.com>;tag=zpNctbZq
To: <sip:adam@example.com>;tag=ie4hbb8t
Call-ID: cdB34qLToC@terminal.example.com
CSeq: 997935768 NOTIFY
Contact: <sip:pres.example.com>
Event: presence
Subscription-State: active;expires=7200
Content-Type: multipart/related;type="application/cpim-pidf+xml";
start="<nXYxAE@pres.example.com>";boundary="50UBfW7LSCVLtggUPe5z"
Content-Length: xxx
--50UBfW7LSCVLtggUPe5z
Content-Transfer-Encoding: 8bit
Content-ID: <nXYxAE@pres.example.com>
Content-Type: application/cpim-pidf+xml;charset="UTF-8"
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:obj="urn:ietf:params:xml:ns:pidf-ext-cont"
entity="sip:john@pres.example.com">
<tuple id="432sd">
<status>
<basic>open</basic>
</status>
<contact>sip:john@im.example.com</contact>
<note>At home</note>
<obj:ObjLink>cid:own_photo@example.com</obj:ObjLink>
<obj:ObjLink>cid:image1@example.com</obj:ObjLink>
</tuple>
</presence>
--50UBfW7LSCVLtggUPe5z
Content-Type: image/jpeg
Content-ID: <own_photo@example.com>
Content-Transfer-Encoding: binary
Content-Description: Own photo
(encoded jpeg image)
--50UBfW7LSCVLtggUPe5z
Content-Type: message/external-body
Content-ID: <image1@example.com>
Content-Disposition: render
Content-Description: Group photo
Content-Type: message/external-body;
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access-type="URL";
expiration="Mon, 24 June 200x 09:00:00 GMT";
URL="http://www.ex.com/company_party/image1.png"
size=234422
--50UBfW7LSCVLtggUPe5z
6.2 External Content Reference in Presence Information without MIME
Multipart Definition
Presence information subscription from client to server:
SUBSCRIBE sip:john@pres.example.com SIP/2.0
Via: SIP/2.0/TCP xxxxx;branch=z9hG4bKwYb6QREiCL
Max-Forwards: 70
To: <sip:john@pres.example.com>
From: <sip:adam@example.com>;tag=ie4hbb8t
Call-ID: cdB34qLToC@terminal.example.com
CSeq: 322723822 SUBSCRIBE
Contact: xxxx
Event: presence
Expires: 7200
Accept: application/cpim-pidf+xml
Accept: image/*
Content-Length: 0
Notification having a link to the picture:
NOTIFY sip:terminal.example.com SIP/2.0
Via: SIP/2.0/TCP pres.example.com;branch=z9hG4bKMgRenTETmm
Max-Forwards: 70
From: <sip:john@pres.example.com>;tag=zpNctbZq
To: <sip:adam@example.com>;tag=ie4hbb8t
Call-ID: cdB34qLToC@terminal.example.com
CSeq: 997935768 NOTIFY
Contact: <sip:pres.example.com>
Event: presence
Subscription-State: active;expires=7200
Content-Type: application/cpim-pidf+xml
Content-Length: xxx
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:cpim-pidf"
xmlns:obj="urn:ietf:params:xml:ns:pidf-ext-cont"
entity="sip:john@pres.example.com">
<tuple id="432sd">
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<status>
<basic>open</basic>
</status>
<contact>sip:john@im.example.com</contact>
<note>At home</note>
<obj:ObjLink ContentType="image/jpeg">http://www.example.com/own_photo.jpg</obj:ObjLink>
</tuple>
</presence>
7. XML Schema Definition
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:pidf-ext-cont"
xmlns:xs=http://www.w3.org/2001/XMLSchema
elementFormDetault="qualified"
attributeFormDefault="unqualified">
<xs:element name="ObjLink">
<xs:complexType>
<xs:simpleContent>
<xs:extension base="xs:anyURI">
<xs:attribute name="ContentType" type=xs:string use="optional"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:/element>
</xs:schema>
8. Security Considerations
All security conciderations defined in [5] and [4] apply this
document.
9. Acknowledgements
The authors would like to thank Aki Niemi for his valuable input.
10. Changes from the Version 00
o Two XML extension elements (ExtLink and CId) were combined
together and named as ObjLink.
o Optional ContentType attribute was added to the ObjLink element.
o References to the syntax of URL and pre-defined scemes were added.
o Content type negotiation related texts were removed from the
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Section 5.
o Some editorial corrections.
References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Sugano, H., "CPIM Presence Information Data Format",
draft-ietf-impp-cpim-pidf-07.txt, December 2002.
[3] Campbell, B., "SIMPLE Presence Publication Mechanism",
draft-olson-simple-publish-02.txt, February 2003.
[4] Olson, S., "A Mechanism for Content Indirection in Session
Initiation Protocol (SIP) Messages",
draft-ietf-sip-content-indirect-mech-01, February 2003.
[5] Rosenberg, J., "Session Initiation Protocol (SIP) Extensions
for Presence", draft-ietf-simple-presence-10.txt, January
2003.
[6] Levinson, E., "The MIME Multipart/Related Content Type", RFC
2387, August 1998.
[7] Palme, J., "MIME Encapsulation of Aggregate Documents", RFC
2557, March 1999.
[8] Freed, N., "Definition of the URL MIME External-Body
Access-Type", RFC 2017, October 1996.
[9] Berners-Lee, T., "Uniform Resource Locators (URL)", RFC 1738,
December 1994.
[10] Levinson, E., "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998.
[11] Freed, N., "Multipurpose Internet Mail Extensions (MIME) Part
One: Format of Internet Message Bodies", RFC 2045, November
1996.
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Authors' Addresses
Mikko Lonnfors
Nokia Research Center
Itamerenkatu 00180
Helsinki
Finland
Phone: + 358 50 4836402
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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