RFC 6502

Conference Event Package Data Format Extension for Centralized Conferencing (XCON)

📅 published March 2012, from ietf

RFC 6502 is the Conference Event Package Data Format Extension for Centralized Conferencing (XCON) 🎀

Category: Standards Track ISSN: 2070-1721 Date: March 2012 Authors: G. Camarillo (Ericsson), S. Srinivasan, R. Even (Gesher Erove Ltd), and J. Urpalainen (Nokia) Obsoletes / Updates: the title block doesn't list anything this one obsoletes or updates 🙈

Abstract ✨

okay so this doc is all about the notification mechanism for XCON (centralized conferencing) 📣 It reuses the SIP (Session Initiation Protocol) event package for conference state, and on top of that the notification mechanism supports the XCON data model and partial notifications 💜

Status of This Memo 📋

This is an Internet Standards Track document 🔥

It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check Section 2 of RFC 5741 🧚

For the current status, any errata, and how to give feedback, go to http://www.rfc-editor.org/info/rfc6502 🌸

Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved 💖

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they stand on the date of publication. Please actually read these, bestie, because they spell out your rights and restrictions for this document. Code Components pulled out of this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License 📜

This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The people controlling the copyright in some of that material may not have given the IETF Trust permission to allow modifications outside the IETF Standards Process. So unless you get an adequate license from those copyright holders, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process. The exceptions are formatting it for publication as an RFC or translating it into languages other than English 🌈

Table of Contents 🗂️

1. Introduction ....................................................3
2. Terminology .....................................................4
3. Notification Formats ............................................5
4. Full Notifications ..............................................5
   4.1. Backwards Compatibility ....................................5
5. Partial Notifications ...........................................6
   5.1. Generation of Partial Notifications ........................6
   5.2. Processing of Partial Notifications ........................7
   5.3. Partial Notification Format ................................8
   5.4. XML Schema for Partial Notifications .......................8
   5.5. Examples ...................................................9
6. IANA Considerations ............................................10
   6.1. MIME type Registration:
        application/xcon-conference-info+xml ......................10
   6.2. MIME type Registration:
        application/xcon-conference-info-diff+xml .................11
   6.3. URN Sub-Namespace Registration:
        xcon-conference-info-diff .................................12
   6.4. XML Schema Registration ...................................12
7. Security Considerations ........................................12
8. References .....................................................13
   8.1. Normative References ......................................13
   8.2. Informative References ....................................13

1. Introduction ✨

okay so the XCON (Centralized Conferencing) framework [RFC5239] defines a notification service that sends updates about a conference instance's state to authorized parties using a notification protocol, as shown in Figure 1 🦋 This document explains how to use the SIP (Session Initiation Protocol [RFC3261]) event package for conference state, which is defined in [RFC4575], as the notification protocol between a client and a conference's notification server 💅

        ...........................
        .  Conferencing System    .
        .                         .
        .    +--------------+     .
        .    | Conf. object |     .
        .    |              |     .
        .    +--------------+     .
        .            |            .
        .            v            .
        .  +------------+         .
        .  |Notification|         .
        .  |Service     |         .
        .  +------------+         .
        .         ^               .
        ..........|................
                  |
                  |       Notification
                  |         Protocol
                  |(notifications following the
                  |      XCON data model)
                  |
        ..........|............
        .         v           .
        .  +------------+     .
        .  |Notification|     .
        .  |   Client   |     .
        .  +------------+     .
        .                     .
        . Conferencing Client .
        .......................

Figure 1: Notification service and protocol in the XCON architecture 🖼️

Besides the SIP event package for conference state, [RFC4575] also specifies a data format to go with it. The XCON data model [RFC6501] extends that format with new elements and attributes, so the extended format can do more stuff, like floor control 👑 The notification protocol in this document supports all the data in the XCON data model, meaning the data originally defined in [RFC4575] plus every extension defined in [RFC6501]. It also adds a partial notification mechanism based on XML patch operations [RFC5261] 🫶

2. Terminology 💅

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] 📖

3. Notification Formats 🍓

To get notifications from a conference server's notification service, a client subscribes to the 'conference' event package at the server, as specified in [RFC4575]. Per [RFC4575], NOTIFY requests in this event package can carry an XML document in the application/conference-info+xml format. This spec also lets NOTIFY requests carry XML documents in the application/xcon-conference-info+xml and the application/xcon-conference-info-diff+xml formats 🌈

A document in the application/xcon-conference-info+xml format gives the user agent the whole state of a conference instance 🌟 A document in the application/xcon-conference-info-diff+xml format gives the user agent just the changes the conference state has gone through since the last notification sent to that user agent 🦋

4. Full Notifications 💖

Subscribers say they support full notifications by including the application/xcon-conference-info+xml format in the Accept header field of the SUBSCRIBE requests they generate. If a client subscribing to the 'conference' event package generates an Accept header field that includes the MIME type application/xcon-conference-info+xml, the server has the option of returning documents that follow the XML format specified in [RFC6501] and are carried in application/xcon-conference-info+xml message bodies ✨

4.1. Backwards Compatibility 🔙

Conference servers that implement the SIP event package for conference state and support the application/xcon-conference-info+xml MIME type MUST also support the application/conference-info+xml MIME type. That way, legacy clients, which only support application/conference-info+xml, can still get notifications in a format they understand 🧸

Clients that implement the SIP event package for conference state and support the application/xcon-conference-info+xml MIME type SHOULD also support the application/conference-info+xml MIME type. That way, these clients can get notifications from legacy servers, which only support application/conference-info+xml, in a format they understand 🫶

5. Partial Notifications 🧩

The conference state reported by this event package may contain lots of elements. When the xcon-conference-info+xml format is used and an element's state changes, the server generates a notification with the whole conference state. Sending big notifications to report small changes does not meet the efficiency requirements of some bandwidth-constrained environments 😭 The partial notifications mechanism in this section is the more efficient way to report changes in conference state 🚀

The SIP event package for conference state defined a partial notification mechanism based on <state> elements. Servers compliant with this specification MUST NOT use that partial notification mechanism. Instead, they MUST use the mechanism specified in this section 🙅‍♀️

Subscribers say they support partial notifications by including the application/xcon-conference-info-diff+xml format in the Accept header field of the SUBSCRIBE requests they generate. If a client subscribing to the 'conference' event package generates an Accept header field that includes the MIME type application/xcon-conference-info-diff+xml, the server has the option of returning documents that follow the XML format specified in Section 5.4 and carried in application/xcon-conference-diff-info+xml message bodies 💜

5.1. Generation of Partial Notifications ✨

Okay bestie, so once a subscription is accepted and installed, the server MUST deliver full state in its first notification. 💖 To report full state, the server MUST set the Content-Type header field to the value application/xcon-conference-info+xml.

To send a partial notification, the server MUST set the Content-Type header field to the value application/xcon-conference-info-diff+xml. When the server makes a partial notification, it SHOULD only include the info that changed since the previous notification. What counts as a "change" is up to the server's local policy. 🦋

The server MUST construct partial notifications using this logic: anything added to the document goes inside <add> elements, anything removed goes inside <remove> elements, and anything changed goes under <replace> elements. 🧚

The server MUST NOT send a new NOTIFY request with a partial notification until it has received a final response from the subscriber for the previous one, or until the previous NOTIFY request has timed out. ⏳

When the server receives a SUBSCRIBE request (refresh or termination) within the associated subscription, it SHOULD send a NOTIFY request containing the full document, using the application/xcon-conference-info+xml content type. 🌸

If the server has been using a content type other than application/xcon-conference-info+xml in notifications on the existing subscription, and it switches over to partial notifications, the server MUST deliver full state using application/xcon-conference-info+xml before it generates its first partial notification. 💅

5.2. Processing of Partial Notifications 🫶

When a subscriber gets the first notification containing full state in an application/xcon-conference-info+xml MIME body, the subscriber MUST store that full document as its local copy.

When the subscriber receives a later notification, the subscriber MUST update its locally stored info using this logic:

  • If the notification carries an application/xcon-conference-info+xml document, the subscriber MUST replace its local copy of the document with the document received in the notification.
  • If the notification carries an application/xcon-conference-info-diff+xml document, the subscriber MUST apply the changes in that diff document to its local copy of the full document.

If the subscriber runs into a processing error while handling an application/xcon-conference-info-diff+xml document, the subscriber SHOULD renew its subscription. 🔄 A subscriber can go back to normal operations by leaving the application/xcon-conference-info-diff+xml format out of a new SUBSCRIBE request.

If the server changes the content type it uses in notifications within the existing subscription, the subscriber MUST discard all the previously received information and process the new content as specified for that content type. 🧹

5.3. Partial Notification Format 🎀

An xcon-conference-info-diff document is an XML [W3C.REC-xml-20081126] document that MUST be well-formed and SHOULD be valid. The namespace URI for the <conference-info-diff> root document element is defined in [RFC6501]:

urn:ietf:params:xml:ns:xcon-conference-info

The root document element <conference-info-diff> has a single mandatory attribute, "entity". Its value is the conference object identifier (XCON-URI) that identifies the conference being described in the document.

The content of <conference-info-diff> is an unordered sequence of <add>, <replace>, and <remove> elements, followed by elements from other namespaces for extensibility. Any such unknown elements MUST be ignored by the client. 🙈 The <add>, <replace>, and <remove> elements can contain extension attributes beyond the ones defined in their corresponding base types in [RFC5261].

5.4. XML Schema for Partial Notifications 📜

This is the XML schema for the "application/xcon-conference-info-diff+xml" data format. The "urn:ietf:params:xml:schema:xml-patch-ops" schema is defined in [RFC5261].

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
 targetNamespace="urn:ietf:params:xml:ns:xcon-conference-info"
 xmlns="urn:ietf:params:xml:ns:xcon-conference-info"
 xmlns:xs="http://www.w3.org/2001/XMLSchema"
 elementFormDefault="qualified">

 <!-- include patch-ops type definitions -->
 <xs:include
  schemaLocation="urn:ietf:params:xml:schema:patch-ops"/>
 <!-- partial updates -->
 <xs:element name="conference-info-diff">
  <xs:complexType>
   <xs:sequence minOccurs="0" maxOccurs="unbounded">
    <xs:choice>
     <!-- add some content -->
     <xs:element name="add">
      <xs:complexType mixed="true">
       <xs:complexContent>

        <xs:extension base="add">
         <xs:anyAttribute processContents="lax"/>
        </xs:extension>
       </xs:complexContent>
      </xs:complexType>
     </xs:element>
     <!-- remove some content -->
     <xs:element name="remove">
      <xs:complexType>
       <xs:complexContent>
        <xs:extension base="remove">
         <xs:anyAttribute processContents="lax"/>
        </xs:extension>
       </xs:complexContent>
      </xs:complexType>
     </xs:element>
     <!-- replace some content -->
     <xs:element name="replace">
      <xs:complexType mixed="true">
       <xs:complexContent>
        <xs:extension base="replace">
         <xs:anyAttribute processContents="lax"/>
        </xs:extension>
       </xs:complexContent>
      </xs:complexType>
     </xs:element>
     <!-- allow extension elements from other namespaces -->
     <xs:any namespace="##other" processContents="lax"/>
    </xs:choice>
   </xs:sequence>
   <xs:attribute name="entity" type="xs:anyURI" use="required"/>
   <xs:anyAttribute processContents="lax"/>
  </xs:complexType>
 </xs:element>
</xs:schema>

5.5. Examples 🍓

The following is an application/xcon-conference-info-diff+xml partial update document:

<?xml version="1.0" encoding="UTF-8"?>
<conference-info-diff
 xmlns="urn:ietf:params:xml:ns:xcon-conference-info"
 entity="conference123@example.com">
 <add
  sel="*/users/allowed-users-list">  <target
  uri="sip:john@example.com" method="refer"/>
  </add>

 <replace sel="*/conference-state/user-count/text()">5</replace>

</conference-info-diff>

6. IANA Considerations 👑

There are four IANA considerations associated with this specification.

6.1. MIME type Registration: application/xcon-conference-info+xml 💜

This section registers the application/xcon-conference-info+xml MIME type.

  • MIME media type name: application
  • MIME subtype name: xcon-conference-info+xml
  • Mandatory parameters: none
  • Optional Parameters: Same as charset parameter application/xml as specified in [RFC3023].
  • Encoding considerations: Same as encoding considerations of application/xml as specified in [RFC3023].
  • Security considerations: Security considerations: See Section 10 of [RFC3023].
  • Interoperability considerations: none
  • Published specification: RFC 6502
  • Applications that use this media type: This document type has been defined to support centralized conferencing applications.
  • Additional Information:
    • Magic Number: none
    • File extension: .xml
    • Macintosh file type code: "TEXT"
  • Personal and email address for further information: IETF XCON Working Group <xcon@ietf.org>
  • Intended usage: COMMON
  • Author/Change controller: The IETF.

6.2. MIME type Registration: application/xcon-conference-info-diff+xml 🦋

This section registers the application/xcon-conference-info-diff+xml MIME type.

  • MIME media type name: application
  • MIME subtype name: xcon-conference-info-diff+xml
  • Mandatory parameters: none
  • Optional Parameters: Same as charset parameter application/xml as specified in [RFC3023].
  • Encoding considerations: Same as encoding considerations of application/xml as specified in [RFC3023].
  • Security considerations: Security considerations: See Section 10 of [RFC3023].
  • Interoperability considerations: none
  • Published specification: RFC 6502
  • Applications that use this media type: This document type has been defined to support partial notifications in centralized conferencing applications.
  • Additional Information:
    • Magic Number: none
    • File extension: .xml
    • Macintosh file type code: "TEXT"
  • Personal and email address for further information: IETF XCON Working Group <xcon@ietf.org>
  • Intended usage: COMMON
  • Author/Change controller: The IETF.

6.3. URN Sub-Namespace Registration: xcon-conference-info-diff 🌈

This section registers a new XML namespace per the procedures in [RFC3688].

  • URI: urn:ietf:params:xml:ns:xcon-conference-info-diff
  • Registrant Contact: IETF SIPPING working group <sipping@ietf.org>, Gonzalo Camarillo <Gonzalo.Camarillo@ericsson.com>
  • XML:
<?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>Partial Notifications in Centralized Conferencing</title>
</head>
<body>
  <h1>Namespace for Partial Notifications in</h1>
  <h1>Centralized Conferencing</h1>
  <h2>urn:ietf:params:xml:ns:xcon-conference-info-diff</h2>
  <p>See <a href="http://www.rfc-editor.org/rfc/rfc6502.txt">
     RFC 6502</a>.</p>
 </body>
</html>

6.4. XML Schema Registration ✨

This section registers an XML schema per the procedures in [RFC3688].

  • URI: urn:ietf:params:xml:schema:xcon-conference-info-diff
  • Registrant Contact: IETF XCON working group, <xcon@ietf.org>, Gonzalo Camarillo <Gonzalo.Camarillo@ericsson.com>

The XML for this schema can be found in Section 5.4.

7. Security Considerations 🔥

This document specifies how to deliver notifications using the SIP event package for conference state in two new formats. The fact that notifications are encoded in a different format does not have security implications. Section 8 of [RFC4575] contains security considerations related to the use of the event package.

Bestie, this part is serious. Implementers of the event package need to follow those considerations regardless of the format used to encode their notifications. No skipping, no cap. 💀

8. References 📚

8.1. Normative References 📚

okay so these are the references the spec leans on hardcore, the ones you need to actually read to get the whole picture 🤓

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3023] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC 3023, January 2001.

[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002.

[RFC4575] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session Initiation Protocol (SIP) Event Package for Conference State", RFC 4575, August 2006.

[RFC5261] Urpalainen, J., "An Extensible Markup Language (XML) Patch Operations Framework Utilizing XML Path Language (XPath) Selectors", RFC 5261, September 2008.

[RFC6501] Novo, O., Camarillo, G., Morgan, D., and J. Urpalainen, "Conference Information Data Model for Centralized Conferencing (XCON)", RFC 6501, March 2012.

[W3C.REC-xml-20081126] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC-xml-20081126, November 2008, <http://www.w3.org/TR/2008/REC-xml-20081126>.

8.2. Informative References 🦋

these ones are more like background reading. super helpful, just not the core rules 💅

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004.

[RFC5239] Barnes, M., Boulton, C., and O. Levin, "A Framework for Centralized Conferencing", RFC 5239, June 2008.

Authors' Addresses 🎀

the squad behind this one 🫶

Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas  02420
Finland

EMail: Gonzalo.Camarillo@ericsson.com


Srivatsa Srinivasan

EMail: srivatsa.srinivasan@gmail.com


Roni Even
Gesher Erove Ltd
14 David Hamelech
Tel Aviv 64953
Israel

EMail: ron.even.tlv@gmail.com


Jari Urpalainen
Nokia
Itamerenkatu 11-13
Helsinki  00180
Finland

EMail: jari.urpalainen@nokia.com
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