Network Working Group                                     H. Schulzrinne
Request for Comments: 3994                                   Columbia U.
Category: Standards Track                                   January 2005


        Indication of Message Composition for Instant Messaging

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 (2005).

Abstract

   In instant messaging (IM) systems, it is useful to know during an IM
   conversation whether 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.





















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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology and Conventions  . . . . . . . . . . . . . . . . .  3
   3.  Description  . . . . . . . . . . . . . . . . . . . . . . . . .  3
       3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . .  3
       3.2.  Message Composer Behavior  . . . . . . . . . . . . . . .  4
       3.3.  Status Message Receiver Behavior . . . . . . . . . . . .  5
       3.4.  Message Content  . . . . . . . . . . . . . . . . . . . .  6
       3.5.  Additional Status Information  . . . . . . . . . . . . .  6
   4.  Using the Status Message . . . . . . . . . . . . . . . . . . .  7
   5.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  XML Document Format  . . . . . . . . . . . . . . . . . . . . .  8
       6.1.  XML Schema . . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
       8.1.  Content-Type Registration for
             'application/im-iscomposing+xml' . . . . . . . . . . . . 10
       8.2.  URN Sub-Namespace Registration for
             'urn:ietf:params:xml:ns:im-iscomposing'  . . . . . . . . 11
       8.3.  Schema Registration  . . . . . . . . . . . . . . . . . . 11
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
       10.1. Normative References . . . . . . . . . . . . . . . . . . 12
       10.2. Informative References . . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 13

1.  Introduction

   By definition, instant messaging (IM) is message based:  A user
   composes a message by, for example, 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 the other
   party is waiting for a response.  If no response is forthcoming, a
   participant in an instant messaging conversation may erroneously
   assume either that 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 sent as soon as one party
   starts typing a message.  In this document, we describe a generalized
   version of this indication, called the isComposing status message.
   As described in Section 3 in more detail, a status message is
   delivered to the instant message recipient in the same manner as are
   the messages themselves.  The isComposing status messages can
   announce the composition of any media type, not just text.  For



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   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.  Below, we will call these
   messages "status messages" for brevity.

   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 PIDF [6], were also
      considered but have a number of disadvantages.  They add more
      overhead, as 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 [7].

2.  Terminology and Conventions

   This memo makes use of the vocabulary defined in the IMPP Model
   document [1].  In this memo, terms such as CLOSED, INSTANT MESSAGE,
   OPEN, PRESENCE SERVICE, PRESENTITY, WATCHER, and WATCHER USER AGENT
   are used with the same meaning 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 2119 [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, which 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 document limited to "idle" and "active".  By
   default, the user is in "idle" state, both before starting to compose
   a message and after sending it.



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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 starts composing a 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 timers: the active-state refresh interval, and
   the idle time-out interval.

   The active-state refresh interval determines how often "active" state
   messages are sent while the composer remains in "active" state.  The
   interval is chosen by the composing user and indicated in the
   <refresh> element in the status message, expressed in integer
   seconds.  Each transmission of the isComposing message resets the
   timer.  The interval SHOULD be no shorter than 60 seconds.  A message
   composer MAY decide not to send active-state refresh messages at all.
   This is indicated by omitting the 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.)  No
   refresh messages are sent in "idle" state.

      The active-state refresh mechanism deals with the case in which
      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.  If the user starts composing again while in
   "idle" state, the state transitions to "active", and the
   corresponding status message is sent.  Unless otherwise configured by
   the user, the idle timeout SHOULD have a default value of 15 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.









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   The state transitions are shown in Figure 1.

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

                   Figure 1. 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; otherwise, it is 120 seconds.  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.









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   The state transitions are shown in Figure 2.

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

                 Figure 2. Receiver State Diagram

3.4.  Message Content

   We briefly describe the message content to summarize the discussion
   above.  This description is non-normative.  The schema (Section 6)
   should be consulted for the normative message format.

   The message consists of an <isComposing> element, with a mandatory
   <state> element indicating the composer state; i.e., idle or active.
   In addition, there are three optional elements: <lastactive>,
   indicating the time of last activity; <contenttype>, the type of
   message being created; and <refresh>, the time interval after which
   the receiver can expect an update from the composer.  Details are
   given in the following section.

3.5.  Additional Status Information

   The status message contains additional optional elements to provide
   further details on the composition activity.  Any of these can appear
   in both "active" and "idle" state messages.








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

   The optional <contenttype> element indicates the type of medium in
   which 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.

   To further describe message composition, 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".  Additional elements MUST use their own namespaces and MUST
   be designed so that receivers can safely ignore such extensions.
   Adding elements to the namespace defined in this document is not
   permitted.

   The isComposing status message MAY be carried in CPIM messages [3].

      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.