Network Working Group H. Schulzrinne Request for Comments: 4482 Columbia U. Category: Standards Track July 2006
CIPID: Contact Information for the Presence Information Data Format
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The Presence Information Data Format (PIDF) defines a basic XML format for presenting presence information for a presentity. The Contact Information for the Presence Information Data format (CIPID) is an extension that adds elements to PIDF that provide additional contact information about a presentity and its contacts, including references to address book entries and icons.
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Table of Contents
1. Introduction ....................................................2 2. Terminology and Conventions .....................................3 3. CIPID Elements ..................................................3 3.1. Card Element ...............................................3 3.2. Display-Name Element .......................................3 3.3. Homepage Element ...........................................3 3.4. Icon Element ...............................................4 3.5. Map Element ................................................4 3.6. Sound Element ..............................................4 4. Example .........................................................4 5. The XML Schema Definition .......................................6 6. IANA Considerations .............................................7 6.1. URN Sub-Namespace Registration for .........................7 'urn:ietf:params:xml:ns:pidf:cipid' 6.2. Schema Registration for Schema 'urn:ietf:params:xml:ns:pidf:cipid' ........................7 7. Internationalization Considerations .............................8 8. Security Considerations .........................................8 9. References ......................................................9 9.1. Normative References .......................................9 9.2. Informative References ....................................10
Presence information facilitates communication; its usefulness can be enhanced by providing basic information about a presentity or contact. This specification describes a basic set of information elements that allow a watcher to retrieve additional information about a presentity or contact.
This specification defines extensions to the PIDF [9] Extensible Markup Language [7][8][10] (XML) document format.
We describe elements for providing a "business card", references to the homepage, map, representative sound, display name, and an icon. This additional presence information can be used in PIDF [9] documents, together with Rich Presence Information Data format [11] (RPID), future-status [12], and other PIDF extensions.
All elements extend the <person> or, less commonly, <tuple> element in the presence data model [13]. The <tuple> element is only extended with Contact Information for the Presence Information Data format (CIPID) elements if the information describes a service referring to another person that is marked by an RPID <relationship> element with a value other than 'self'. All elements described in this document are optional.
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RPID and CIPID both provide "rich" presence that goes beyond the basic 'open' and 'closed' status information in PIDF. The presence information described in these two documents can be supplied independently, although in practice, both will often appear in the same PIDF document. CIPID elements describe the more static aspects of somebody's presence information, while RPID focuses on elements that will likely change throughout the day. Thus, CIPID information can often be statically configured by the user through the graphical user interface of a presence client; this is less likely to be sufficient for RPID.
The namespace URI for these elements defined by this specification is a URN [2], using the namespace identifier 'ietf' defined by [4] and extended by [6]:
The key words MUST, MUST NOT, REQUIRED, SHOULD, SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL in this document are to be interpreted as described in BCP 14, RFC 2119 [1].
The <display-name> element includes the name identifying the tuple or person that the presentity suggests should be shown by the watcher user interface. It is left to the watcher user interface design to choose whether to heed this suggestion or to use some other suitable string. The CIPID information MAY contain multiple display names, but only if they are labeled with different 'xml:lang' attributes. This allows a Korean-speaking presentity to convey its display name in different languages, Latin and Hangul, for example.
The <icon> element provides a URI pointing to an image (icon) representing the tuple or person. The watcher can use this information to represent the tuple or person in a graphical user interface. Presentities SHOULD provide images of sizes and aspect ratios that are appropriate for rendering as an icon. Support for JPEG, PNG, and GIF formats is REQUIRED.
The <map> element provides a URI pointing to a map related to the tuple or person. The watcher can use this information to represent the tuple or person in a graphical user interface. The map may be either an image, an HTML client-side image map, or a geographical information system (GIS) document, e.g., encoded as GML. Support for images formatted as PNG and GIF is REQUIRED.
The <sound> element provides a URI pointing to a sound related to the tuple or person. The watcher MAY use the sound object, such as a MIDI or MP3 file, referenced by the URL to inform the watcher that the presentity has assumed the status OPEN. Implementors are advised to create user interfaces that provide the watcher with the opportunity to choose whether to play such sounds. Support for sounds coded as MPEG-2 Layer 3 (MP3) is RECOMMENDED. The sound object might also be used to indicate how to pronounce the presentity's name.
This document calls for IANA to register a new XML namespace URN and schema per [6].
6.1. URN Sub-Namespace Registration for 'urn:ietf:params:xml:ns:pidf:cipid'
URI: urn:ietf:params:xml:ns:pidf:cipid Description: This is the XML namespace for XML elements defined by RFC 4482 to describe contact information presence information extensions for the status element in the PIDF presence document format in the application/pidf+xml content type. Registrant Contact: IETF, SIMPLE working group, simple@ietf.org; Henning Schulzrinne, hgs@cs.columbia.edu 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>CIPID: Contact Information for the Presence Information Data Format</title> </head> <body> <h1>Namespace for contact information presence extension (status)</h1> <h2>urn:ietf:params:xml:ns:pidf:cipid</h2> <p>See <a href="http://www.rfc-editor.org/rfc/rfc4482.txt"> RFC4482</a>.</p> </body> </html> END
6.2. Schema Registration for Schema 'urn:ietf:params:xml:ns:pidf:cipid'
URI: urn:ietf:params:xml:ns:pidf:cipid Registrant Contact: IESG XML: See Figure 1
CIPID delivers only URLs, except for the <display-name> element. The resolution of the URLs can negotiate appropriate language and character sets within the URL-designated protocol.
For the display name and to handle Internationalized Resource Identifiers (IRIs) [16], since CIPID is represented in XML, it provides native support for encoding information using the Unicode character set and its more compact representations including UTF-8. Conformant XML processors recognize both UTF-8 and UTF-16. Though XML includes provisions to identify and use other character encodings through use of an "encoding" attribute in an <?xml?> declaration, use of UTF-8 is RECOMMENDED in environments where parser encoding support incompatibility exists.
The XML 'xml:lang' attribute can be used to identify the language and script for the <display-name> element. The specification allows multiple occurrences of this element so that the presentity can convey display names in multiple scripts and languages. If no 'xml: lang' attribute is provided, the default value is "i-default" [3].
The security issues are similar to those for RPID [11]. Watchers need to restrict which content types of content pointed to by <icon>, <homepage>, <map>, <sound>, and <vcard> elements they render.
Also, when a watcher accesses these URIs, the presentity may deduce that the watcher is currently using the presence application. Thus, a presence application concerned about leaking this information may want to cache these objects for later use. (A presentity could easily customize the URLs for each watcher, so that it can tell who is referencing the objects.) This caching behavior may cause the information to become stale, out-of-sync with the current data until the cache is refreshed. Fortunately, the elements in CIPID are expected to retain the same content for periods measured in days, so that privacy-conscious applications may well decide to perform caching over durations that reveal little current activity information. Presentities need to keep in mind that clients may cache the content referenced by URIs for long periods as they use their presence system to construct presence documents using this extension. If the referenced content needs to change frequently, the presentity could, for example, update the presence document with a new URI to encourage clients to notice.
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Icons and other URIs in this document could be used as a covert channel to convey messages to the watcher, outside the content monitoring that might be in place for instant messages or other communications channels. Thus, entities that worry about such channels may want to prohibit the usage of URLs pointing to resources outside their domain, for example.
Implementors must take care to adhere to the mechanisms for verifying the identity in the referenced server's certificate against the URI. For instance, if the URI scheme is https, the requirements of RFC 2818 [5], section 3.1, must be met. In particular, the domain represented in the URI must match the subjectAltName in the certificate presented by the referenced server. If this identity check fails, the referenced content SHOULD NOT be retrieved and MUST NOT be used.
[3] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998.
[4] Moats, R., "A URN Namespace for IETF Documents", RFC 2648, August 1999.
[5] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.
[6] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004.
[7] Maloney, M., Beech, D., Thompson, H., and N. Mendelsohn, "XML Schema Part 1: Structures Second Edition", W3C REC REC- xmlschema-1-20041028, October 2004.
[8] Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes Second Edition", W3C REC REC-xmlschema-2-20041028, October 2004.
[9] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, "Presence Information Data Format (PIDF)", RFC 3863, August 2004.
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[10] Yergeau, F., Paoli, J., Sperberg-McQueen, C., Bray, T., and E. Maler, "Extensible Markup Language (XML) 1.0 (Third Edition)", W3C REC REC-xml-20040204, February 2004.
[11] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. Rosenberg, "RPID: Rich Presence Extensions to the Presence Information Data Format (PIDF)", RFC 4480, July 2006.
[12] Schulzrinne, H., "Timed Presence Extensions to the Presence Information Data Format (PIDF) to Indicate Status Information for Past and Future Time Intervals", RFC 4481, July 2006.
[13] Rosenberg, J., "A Data Model for Presence", RFC 4479, July 2006.
[14] Dawson, F. and T. Howes, "vCard MIME Directory Profile", RFC 2426, September 1998.
[15] Good, G., "The LDAP Data Interchange Format (LDIF) - Technical Specification", RFC 2849, June 2000.
[16] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005.
Acknowledgements
This document is based on discussions within the IETF SIMPLE working group. Spencer Dawkins, Vijay Gurbani, Avshalom Houri, Hisham Khartabil, Paul Kyzivat, Eva Leppanen, Mikko Lonnfors, Aki Niemi, Jon Peterson, Jonathan Rosenberg, and Robert Sparks provided helpful comments.
Author's Address
Henning Schulzrinne Columbia University Department of Computer Science 450 Computer Science Building New York, NY 10027 US
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