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Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

In instant messaging (IM) systems, it is useful to know during an IM conversation that the other party is composing a message, e.g., typing or recording an audio message. This document defines a new status message content type and XML namespace that conveys information about a message being composed. The status message can indicate the composition of a message of any type, including text, voice or video. The status messages are delivered to the instant messaging recipient in the same manner as the instant messages themselves.

Table of Contents

1.  Introduction
2.  Terminology and Conventions
3.  Description
    3.1  Overview
    3.2  Message Composer Behavior
    3.3  Status Message Receiver Behavior
    3.4  Additional Status Information
4.  Using the Status Message
5.  Examples
6.  XML Schema Definition
7.  Security Considerations
8.  IANA Considerations
    8.1  Content-Type Registration for 'application/im-iscomposing+xml'
    8.2  URN Sub-Namespace Registration for 'urn:ietf:params:xml:ns:im-iscomposing'
9.  Acknowledgements
§.  Normative References
§.  Informative References
§  Author's Address
§  Intellectual Property and Copyright Statements

1. Introduction

By definition, instant messaging (IM) is message-based, i.e., a user composes a message by typing, speaking or recording a video clip. This message is then sent to one or more recipients. Unlike email, instant messaging is often conversational, so that the other party is waiting for a response. If no response is forthcoming, a participant in an instant messaging conversation may erroneously assume that either the communication partner has left or that it is her turn to type again, leading to two messages "crossing on the wire".

To avoid this uncertainty, a number of commercial instant messaging systems feature an "is-typing" indication that is sent as soon as one party starts typing a message. In this document, we describe a generalized version of this indication, called isComposing. As described in Section 3 in more detail, a status message is delivered to the instant message recipient in the same manner as the messages themselves. The isComposing messages can announce the composition of any media type, not just text. For example, it might be used if somebody is recording an audio or video clip. In addition, it can be extended to convey other instant messaging user states in the future.

The status messages are carried as XML, as instances of the XML schema defined in Section 6 and labeled as an application/im-iscomposing+xml content type.

These status messages can be considered somewhat analogous to the comfort noise packets that are transmitted in silence-suppressed interactive voice conversations.

Events and extensions to presence, such as PIDFSugano, H. and S. Fujimoto, Presence Information Data Format (PIDF), May 2003.[5], were also considered, but have a number of disadvantages. They add more overhead, since an explicit and periodic subscription is required. For page-mode delivery, subscribing to the right user agent and set of messages may not be easy. An in-band, message-based mechanism is also easier to translate across heterogeneous instant messaging systems.

The mechanism described here aims to satisfy the requirements in [6]Rosenberg, J., Advanced Instant Messaging Requirements for the Session Initiation Protocol (SIP), February 2004..

2. Terminology and Conventions

This memo makes use of the vocabulary defined in the IMPP Model document [1]Day, M., Rosenberg, J. and H. Sugano, A Model for Presence and Instant Messaging, February 2000.. Terms such as CLOSED, INSTANT MESSAGE, OPEN, PRESENCE SERVICE, PRESENTITY, WATCHER, and WATCHER USER AGENT in this memo are used in the same meaning as defined therein. 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 2119Bradner, S., Key words for use in RFCs to Indicate Requirement Levels, March 1997.[2].

This document discusses two kinds of messages, namely the instant message (IM) conveying actual content between two or more users engaged in an instant messaging conversation, and the status message, described in this document, that indicates the current composing status to the other participants in a conversation. We use the terms "content message" and "status message" for these two message types.

3. Description

3.1 Overview

We model the user of an instant messaging system as being in one of several states, in this draft limited to "idle" and "active". By default, the user is in "idle" state, both before starting to compose a message and after sending it.

3.2 Message Composer Behavior

Only the instant messaging user agent actively composing a content message generates status messages indicating the current state. When the user first starts composing an content message (the actual instant message), the state becomes "active" and an isComposing status message containing a <state> element indicating "active" is sent to the recipient of the content message being composed. As long as the user continues to produce instant message content, the user remains in state "active".

There are two sender timeouts, the refresh time-out interval and the idle time-out interval. The composing user MAY specify a refresh time-out interval measured in seconds, using the <timeout> element in the status message, after which the isComposing status message is resent to refresh the state. The refresh period SHOULD be no shorter than 60 seconds. A message composer MAY decide not to send refresh messages at all and thus indicate no refresh interval; this will cause the receiver to assume that it has gone idle after 120 seconds. (In most cases, the content message will have been sent by then.)

The refresh mechanism deals with the case that the user logs off or the application crashes before the content message is completed.

If the user stops composing for more than a configured time interval, the idle timeout, the state transitions to "idle" and an "idle" status message is sent. When the user starts composing again while in "idle" state, the state transitions to "active", with the corresponding status message being sent. Unless otherwise configured by the user, the idle timeout SHOULD have a default value of fifteen seconds.

If a content message is sent before the idle threshold expires, no "idle" state indication is needed. Thus, in most cases, only one status message is generated for each content message. In any event, the message rate is limited to one status message per refresh threshold interval.

The state transitions are shown in Figure 1.

                        +-------------+
                        |+-----------+|
                        ||           ||
                 +------>|   idle    |<------+
                 |      ||           ||      |
                 |      |+-----------+|      |
                 |      +------+------+      |
                 |             |             | idle timeout
content msg. sent|             |composing    | w/o activity
-----------------|             |-------------| ------------------
      --         |             |"active" msg.| "idle" status msg.
                 |      +------V------+      |
                 |      |             |      |
                 |      |             |      |
                 |      |             |      |
                 +------+   active    +------+
                        |             |
                        |             |
                        +-------------+

Sender state diagram

3.3 Status Message Receiver Behavior

The status message receiver uses the status messages to determine the state of the content message sender. If the most recent "active" status message contained a <refresh> value, the refresh time-out is set to that value; it is 120 seconds otherwise. The state at the receiver transitions from "active" to "idle" under three conditions:

1. A status message with status "idle" is received.
2. A content message is received.
3. The refresh interval expires.

Receivers MUST be able to handle multiple consecutive isComposing messages with "active" state regardless of the refresh interval.

The state transitions are shown in Figure 2.

                         +-------------+
                         |+-----------+|
                         ||           ||
                  +------>|   idle    |<------+
                  |      ||           ||      |
                  |      |+-----------+|      |
                  |      +------+------+      |
                  |             |             |
     "idle" recd. |             |"active" msg.| refresh timeout
 or content recd. |             |             | or 120s
                  |             |             |
                  |      +------V------+      |
                  |      |             |      |
                  |      |             |      |
                  |      |             |      |
                  +------+   active    +------+
                         |             |
                         |             |
                         +-------------+

Receiver state diagram

3.4 Additional Status Information

The status message contains additional optional elements to provide further details on the composition activity.

The optional <lastactive> element describes the absolute time when the user last added or edited content.

The optional <contenttype> element indicates what type of media the messaging terminal is currently composing. It can contain either just a MIME media type, such as "audio" or "text", or a media type and subtype, such as "text/html". It is best understood as a hint to the user, not a guarantee that the actual content message will indeed contain only the content indicated. It allows the human recipient to be prepared for the likely message format.

The XML schema or the set of allowable state names can be extended in future documents. Recipients of status messages implementing this specification without extensions MUST treat state tokens other than "idle" and "active" as "idle".

The isComposing status message MAY be carried in CPIM messages [3]Atkins, D. and G. Klyne, Common Presence and Instant Messaging: Message Format, January 2003..

Such a wrapper is particularly useful if messages are relayed by a conference server since the CPIM message maintains the identity of the original composer.

4. Using the Status Message

The isComposing status message can be used with either page mode or session mode, although it is a more natural fit with session mode. In session mode, the status message is sent as part of the messaging stream. Its usage is negotiated just like any other media type in a stream is negotiated, i.e., through SDP. Sending the status messages within the messaging stream has several benefits. First, it ensures proper ordering and synchronization with the actual content messages being composed. In messaging systems that guarantee in-order delivery of messages, this approach avoids that message reordering across two delivery mechanisms has an active indication appear at the receiver after the actual message has been delivered.

Secondly, end-to-end security can be applied to the messages. Thirdly, SDP negotiation mechanisms can be used to turn it on and off at any time, and even negotiate its use in a single direction at a time.

Usage with page mode is also straightforward. There, the status message is carried as the body of a page mode message. Unfortunately, there is no way to negotiate its usage, turn it on or off, or even be sure that the status message gets delivered before the actual content being composed arrives. (However, in SIP, page mode is limited to one unacknowledged message, so that out-of-order delivery is unlikely, albeit still possible if proxies are involved.)

5. Examples

<?xml version="1.0" encoding="UTF-8"?>
  <isComposing xmlns="urn:ietf:params:xml:ns:im-iscomposing"
    <state>active</state>
    <contenttype>text/plain</contenttype>
    <timeout>90</timeout>
    <lastactivity>2003-01-27T10:43:00Z</lastactivity>
  </isComposing>

<?xml version="1.0" encoding="UTF-8"?>
  <isComposing xmlns="urn:ietf:params:xml:ns:im-iscomposing"
    <state>idle</state>
    <contenttype>audio</contenttype>
    <lastactivity>2003-01-27T10:43:00Z</lastactivity>
  </isComposing>

6. XML Schema Definition

An isComposing document is an XML document that MUST be well-formed and SHOULD be valid. isComposing documents MUST be based on XML 1.0 and MUST be encoded using UTF-8. This specification makes use of XML namespaces for identifying isComposing documents. The namespace URI for elements defined for this purpose is a URN, using the namespace identifier 'ietf'. This URN is:

urn:ietf:params:xml:ns:im-iscomposing

  <?xml version="1.0" encoding="UTF-8"?>
  <xs:schema 
     targetNamespace="urn:ietf:params:xml:ns:im-iscomposing"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     xmlns:tns="urn:ietf:params:xml:ns:im-iscomposing"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">

     <xs:import namespace="http://www.w3.org/XML/1998/namespace"
     schemaLocation="http://www.w3.org/2001/xml.xsd"/>

    <xs:element name="isComposing">
      <xs:sequence>
        <xs:element name="state" type="xs:string" />
        <xs:element name="lastactive" type="xs:dateTime"
          minOccurs="0"/>
        <xs:element name="contenttype" type="xs:string"
          minOccurs="0"/>
        <xs:element name="refresh" type="xs:positiveInteger"
          minOccurs="0"/>
        <xs:any namespace="##other" processContents="lax"
          minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
    </xs:element>
  </xs:schema>

7. Security Considerations

The isComposing indication provides a fine-grained view of the activity of the entity composing and thus deserves particularly careful confidentiality protection so that only the intended destination of the message will receive the isComposing indication.

Since the status messages are carried using the IM protocol itself, all security considerations of the underlying IM protocol apply also to the isComposing status messages.

There are potential privacy issues in sending isComposing status messages before an actual conversation has been established between the communicating users. A status message may be sent even if the user later abandons the message. It is RECOMMENDED that isComposing indications in page-mode are only sent when a message is being composed as a reply to an earlier message. This document does not prescribe how an implementation detects in page mode whether a message is in response to an earlier one, but elapsed time or user interface behavior might be used as hints.

8. IANA Considerations

8.1 Content-Type Registration for 'application/im-iscomposing+xml'

To:

ietf-types@iana.org

Subject:

Registration of MIME media type application/im-iscomposing+xml

MIME media type name:

application

MIME subtype name:

im-iscomposing+xml

Required 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 3023Murata, M., St. Laurent, S. and D. Kohn, XML Media Types, January 2001.[4], section 3.2.

Security considerations:

This content type is designed to carry information about current user activity, which may be considered private information. Appropriate precautions should be adopted to limit disclosure of this information.

Interoperability considerations:

This content type provides a common format for exchange of composition activity information.

Published specification:

XXXX (this document)

Applications which use this media type:

Instant messaging systems.

Additional information:

none

Person & email address to contact for further information:

Henning Schulzrinne, hgs@cs.columbia.edu

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.

Other information:

This media type is a specialization of application/xml RFC 3023Murata, M., St. Laurent, S. and D. Kohn, XML Media Types, January 2001.[4], and many of the considerations described there also apply to application/im-iscomposing+xml.

8.2 URN Sub-Namespace Registration for 'urn:ietf:params:xml:ns:im-iscomposing'

URI:

urn:ietf:params:xml:ns:im-iscomposing

Description:

This is the XML namespace for XML elements defined by RFCXXXX to describe composition activity by an instant messaging client using the application/im-iscomposing+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>Is-composing Indication for Instant Messaging</title>
   </head>
   <body>
       <h1>Namespace for SIMPLE iscomposing extension</h1>
       <h2>application/im-iscomposing+xml</h2>
       <p>See <a href="[URL of published RFC]">RFCXXXX</a>.</p>
    </body>
    </html>
   END

9. Acknowledgements

Niemi Aki, Ben Campbell, Miguel Garcia, Christian Jansson, Cullen Jennings, Hisham Khartabil, Jonathan Rosenberg and Xiaotao Wu provided helpful comments.

10. References

10.1 Normative References

10.2 Informative References

Author's Address

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