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.
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
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.
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 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
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.
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 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.
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 element, with a mandatory
element indicating the composer state; i.e., idle or active.
In addition, there are three optional elements: ,
indicating the time of last activity; , the type of
message being created; and , 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.
The optional element describes the absolute time when
the user last added or edited content.
The optional 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.
4. Using the Status Message
The isComposing status message can be used with either page mode or
session mode, although session mode is a more natural fit. 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
that stream, with details depending on the session mode protocol.
Sending the status messages within the session-mode messaging stream
has at least three 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 having an active indication appear at the receiver
after the actual message has been delivered, due to message
reordering across two delivery mechanisms.
Secondly, end-to-end security can be applied to the messages.
Thirdly, session negotiation mechanisms can be used to turn it on and
off at any time, and even to negotiate its use in a single direction
at a time.
Usage with page mode is also straightforward: The status message is
carried as the body of a page mode message. In SIP-based IM, The
composer MUST cease transmitting status messages if the receiver
returned a 415 status code (Unsupported Media Type) in response to a
MESSAGE request containing the status indication.
The sender cannot be assured that the status message is delivered
before the actual content being composed arrives. However, SIP page
mode is limited to one unacknowledged message, so out-of-order
delivery is unlikely, albeit still possible if proxies are involved.
5. Examples
active
text/plain
90
idle
2003-01-27T10:43:00Z
audio
6. XML Document Format
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 by 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
6.1. XML 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
recipient of the message will receive the isComposing indication.
Since the status messages are carried by using the IM protocol
itself, all security considerations of the underlying IM protocol
also apply 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 whether a message is in
response to an earlier one in page mode, 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 3023 [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: RFC 3994
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 the mailing list address
simple@ietf.org.
Other information: This media type is a specialization of
application/xml RFC 3023 [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
RFC 3994 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
Namespace for SIMPLE iscomposing extension
urn:ietf:params:xml:ns:im-composing
See RFC3994.
END
8.3. Schema Registration
This section registers a new XML schema per the procedures in [5].
URI: urn:ietf:params:xml:schema:im-composing
Registrant Contact: IETF, SIMPLE working group, (simple@ietf.org),
Henning Schulzrinne (hgs@cs.columbia.edu).
The XML for this schema can be found as the sole content of Section
6.1.
9. Acknowledgements
Ben Campbell, Miguel Garcia, Scott Hollenbeck, Christian Jansson,
Cullen Jennings, Hisham Khartabil, Allison Mankin, Aki Niemi,
Jonathan Rosenberg, and Xiaotao Wu provided helpful comments.
10. References
10.1. Normative References
[1] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and
Instant Messaging", RFC 2778, February 2000.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Klyne, G. and D. Atkins, "Common Presence and Instant Messaging
(CPIM): Message Format", RFC 3862, August 2004.
[4] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types", RFC
3023, January 2001.
[5] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January
2004.
10.2. Informative References
[6] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and
J. Peterson, "Presence Information Data Format (PIDF)", RFC
3863, August 2004.
[7] Rosenberg, J., "Advanced Instant Messaging Requirements for the
Session Initiation Protocol (SIP)", Work in Progress, February
2004.
Author's Address
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
EMail: hgs@cs.columbia.edu
URI: http://www.cs.columbia.edu/~hgs
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