Internet Engineering Task Force
Internet Draft H. Schulzrinne
Columbia U.
draft-schulzrinne-simple-iscomposing-00.txt
February 24, 2003
Expires: August 2003
is-composing Indication for Instant Messaging Using the Session
Initiation Protocol (SIP)
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
In instant messaging systems, it is useful to know that the other
party is composing a message, e.g., typing. This document defines a
new content type and XML namespace that conveys information about a
message being composed. The message could be of any type, including
text, voice or video.
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1 Introduction
By definition, instant messaging is message-based, i.e., a user
composes a message by typing, speaking or recording a video clip.
This message is then sent. Unlike email, instant messaging is often
conversational, so that the other party is waiting for a response. If
no response is forthcoming, an IM participant side may erroneously
assume that either the communication partner has left or that it is
her turn to type again, leading to messaging "crossing on the wire".
A number of commercial instant messaging systems feature an "is
typing" indication that is set as soon as one party starts typing a
message. In this document, we describe a generalized version of this
indication. It applies to the composition of any media type, not just
text. For example, it might be used if somebody is recording an audio
or video clip.
This indication can be considered somewhat analogous to the comfort
noise packets that are transmitted in silence-suppressed interactive
voice conversations.
The mechanism described here aims to satisfy the requirements in [3].
2 Terminology and Conventions
This memo makes use of the vocabulary defined in the IMPP Model
document [1]. Terms such as CLOSED, INSTANT MESSAGE, OPEN, PRESENCE
SERVICE, PRESENTITY, WATCHER, and WATCHER USER AGENT in the memo are
used in the same meaning as defined therein. The key words MUST,
MUSTNOT, REQUIRED, SHOULD, SHOULDNOT, RECOMMENDED, MAY, and OPTIONAL
in this document are to be interpreted as described in BCP XX, RFC
2119 [2].
3 Description
There are two modes of operation, a keep-alive and two-state mode. In
keep-alive mode, an IM terminal where the user is actively composing
a message sends an update every few seconds if there has been
activity such as typing. The messages cease if there is no sign of
activity during the last interval. This mode has the advantage that
the rate of is-composing indications is constant, but it adds
unnecessary overhead for the common case that a message is composed
in one uninterrupted activity. The keep-alive mode would be useful if
the is-composing indication can convey additional information, such
as the amount of content that has been produced. Such fine-grained
information seems of little practical use, however.
We choose a two-state mode with the states "idle" and "active". As
long as the user produces message content, the state remains active.
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If the user stops composing for more than a configured time interval,
the idle threshold, the state transitions to idle. If a message is
sent before the idle threshold expires, no idle state indication is
needed. Thus, in most cases, only one message is needed. The message
rate is limited to one message per idle threshold interval.
The <contenttype> can contain either just a MIME media type or a
media type and subtype.
The idle threshold SHOULD be ten seconds.
The XML schema can be extended in the future.
We chose XML since this also makes it possible to easily
turn this into event notification. This is likely only
useful for third-party notifications, i.e., notifying event
recipients other than the recipient of the MESSAGE.
Events 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 gateway into non-SIP systems.
4 Using the Indicator
The is-composing indicator can be used with either SIP page mode or
session mode, although it is a more natural fit with session mode. In
session mode, the indicator is sent as part of the messaging stream.
Its usage is negotiated just like support for any other media type in
a stream is negotiated, i.e., through SDP. Sending the indicators
within the messaging stream has many benefits. First, it ensures
proper sequencing and synchronization with the actual messages being
composed. 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 the page mode is also straightforward. The indicator would
be 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 indicator gets delivered before the actual content being
composed.
5 Example
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<?xml version="1.0" encoding="UTF-8"?>
<isComposing xmlns="urn:ietf:params:xml:ns:sip-iscomposing"
<state>active</active>
<contenttype>text/plain</contenttype>
<lastactivity>2003-01-27T10:43:00Z</lastactivity>
</isComposing>
<?xml version="1.0" encoding="UTF-8"?>
<isComposing xmlns="urn:ietf:params:xml:ns:sip-iscomposing"
<state>idle</active>
<contenttype>audio</contenttype>
<lastactivity>2003-01-27T10:43:00Z</lastactivity>
</isComposing>
6 XML Schema Definitions
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="urn:ietf:params:xml:ns:sip-iscomposing"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:tns="urn:ietf:params:xml:ns:sip-iscomposing"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- This import brings in the XML language attribute xml:lang-->
<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="status" type="tns:status"
minOccurs="1"/>
<xs:element name="lastactive" type="xs:dateTime"
minOccurs="0"/>
<xs:element name="contenttype" type="xs:string" minOccurs="0"
maxOccurs="1"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:element>
<xs:simpleType name="status">
<xs:restriction base="xs:string">
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<xs:enumeration value="active"/>
<xs:enumeration value="idle"/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
7 Security Considerations
The is-composing 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 is-composing indication.
8 IANA Considerations
8.1 Content-Type Registration for
To: ietf-types@iana.org
Subject: Registration of MIME media type application/sip-
iscomposing+xml
MIME media type name: application
MIME subtype name: sip-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 [RFC 3023], 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: RFCXXXX (this document)
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Applications which use this media type: Instant messaging
systems.
Additional information: none
Person & email address to contact for further information:
Henning Schulzrinne
E-mail: 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 3023], and many of the considerations
described there also apply to application/sip-
iscomposing+xml.
8.2 URN Sub-Namespace Registration for
URI: urn:ietf:params:xml:ns:sip-iscomposing
Description: This is the XML namespace for XML elements defined
by RFCXXXX to describe composition activity by SIP-based
instant message client using the
application/sip-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 Using the
Session Initiation Protocol (SIP)</title>
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</head>
<body>
<h1>Namespace for SIMPLE iscomposing extension</h1>
<h2>application/sip-iscomposing+xml</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
9 Acknowledgements
Jonathan Rosenberg and Xiaotao Wu provided helpful comments.
10 References
11 Normative References
[1] M. Day, J. Rosenberg, and H. Sugano, "A model for presence and
instant messaging," RFC 2778, Internet Engineering Task Force, Feb.
2000.
[2] S. Bradner, "Key words for use in rfcs to indicate requirement
levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.
12 Informative References
[3] J. Rosenberg, "Advanced instant messaging requirements for the
session initiation protocol (SIP)," internet draft, Internet
Engineering Task Force, Dec. 2002. Work in progress.
13 Authors' and Editor's Addresses
Henning Schulzrinne
Dept. of Computer Science
Columbia University
1214 Amsterdam Avenue
New York, NY 10027
USA
Email: schulzrinne@cs.columbia.edu
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Table of Contents
1 Introduction ........................................ 2
2 Terminology and Conventions ......................... 2
3 Description ......................................... 2
4 Using the Indicator ................................. 3
5 Example ............................................. 3
6 XML Schema Definitions .............................. 4
7 Security Considerations ............................. 5
8 IANA Considerations ................................. 5
8.1 Content-Type Registration for ....................... 5
8.2 URN Sub-Namespace Registration for .................. 6
9 Acknowledgements .................................... 7
10 References .......................................... 7
11 Normative References ................................ 7
12 Informative References .............................. 7
13 Authors' and Editor's Addresses ..................... 7
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