SIMPLE WG M. Lonnfors
Internet-Draft Nokia Research Center
Expires: October 6, 2003 E. Leppanen
H. Khartabil
Nokia
April 7, 2003
BINPIDF - External Object Extension to Presence Information Data
Format
draft-lonnfors-simple-binpidf-00
Status of this Memo
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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 SIP 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 Operation . . . . . . . . . . . . . . . . . . . . 3
4. BINPIDF Elements . . . . . . . . . . . . . . . . . . . . . . . 4
4.1 Namespace . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2 'CId' Element . . . . . . . . . . . . . . . . . . . . . . . . 4
4.3 'ExtLink' 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
References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 9
Intellectual Property and Copyright Statements . . . . . . . . 10
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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, belonging to 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 SIP message while
external objects are referenced indirectly.
There is also need to deliver the external objects in the payload of
a SIP message. The MIME Multipart/Related content type [6] provides a
good basis for placing a reference to external contents as
multiparts. An extension to PIDF is needed for referencing the
multiparts from the PIDF XML formatted presence information. 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 Operation
This section provides an overview of operation for having references
to external objects (direct and indirect content) in presence
information.
The external object can be embedded as one part of a multipart
payload of the SIP 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
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 a content id
(CId) and external link (ExtLink) XML elements. Each separate
external content has its own CId or ExtLink value within presence
information. The value of CId is the Content ID of the external
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object part in the multipart payload. The value of the ExtLink is a
URL to the location where the external content can be fetched.
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 'CId' Element
The 'CId' XML element contains a reference to the part in the
multipart payload where either the content can be directly found or
where further information can be found about the external body. The
CId value corresponds to the Content ID parameter of the multipart
made according to MIME Multipart/Related content type [6].
4.3 'ExtLink' Element
The 'ExtLink' XML element contains an URL [9] to a location where the
external content can be fetched.
5. How To Utilize this Specification
This chapter describes how the payload of SIP messages is composed
when there is a need to convey external objects to XML encoded
presence information document between the client and presence server.
Three different methods are presented in the subsections below
whereby external objects can be delivered: direct link to external
content within PIDF based XML document, and reference to multipart
having either the content of the external object embedded or a URL
(and other information) to external location where the content is
stored.
The client is able to indicate the support for different types of
external objects and the ways of delivering the contents within the
SIP message using the Accept header in the SIP SUBSCRIBE request. The
server handling the message uses the content types supported by the
client for delivering the external objects.
5.1 Direct Link to External Content
The ExtLink 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 CId 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 CId 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: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:CId>link_to_direct_picture_own_photo.jpg</obj:cId>
<obj:CId>link_to_indirect_pict.png</obj:cId>
</tuple>
</presence>
--50UBfW7LSCVLtggUPe5z
Content-Type: image/jpeg
Content-ID: <link_to_direct_picture_own_photo.jpg>
Content-Transfer-Encoding: binary
Content-Description: Own photo
(encoded jpeg image)
--50UBfW7LSCVLtggUPe5z
Content-Type: message/external-body
Content-ID: <link_to_indirect_pict.png>
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: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:ExtLink>http://link_to_direct_picture_own_photo.jpg</obj:ExtLink>
</tuple>
</presence>
7. XML Schema Definition
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:ext-cont"
xmlns:xs=http://www.w3.org/2001/XMLSchema
elementFormDetault="qualified"
attributeFormDefault="unqualified">
<xs:element name="CId" type=xs:string />
<xs:element name="ExtLink" type=anyURI />
</xs:schema>
8. Security Considerations
All security conciderations defined in [5] and [4] apply this
document.
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.
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[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.
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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