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multi-party real-time text charter-01p.txt
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multi-party real-time text charter-01p.txt
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multi-party-real-time-text-01p
21 October 2019
IETF charter for Multi-party handling of Real-time text.
Real-time text is text media used in conversational services, transmitted
and presented at the rate it is created. That is intended to creates a
sense of direct contact between the sender and receiver just as real-time
voice and video communication does.
Real-time text is used by its own in calls as well as in combination with
audio and/or video.
A number of higher level standards requires availability of multi-party
real-time text. Multi-party real-time text can be arranged by standardized
mechanisms in a number of ways. However no current standard is sufficient
explicit about any recommended method for provision of multi-party
real-time text to assure proper presentation in end-user devices.
The work described by this charter is intended to create IETF documents
specifying recommended methods for provision of multi-party real-time text.
The goal is to specify multi-party real-time text for cases when
ITU-T T.140 presentation protocol for real-time text is used, The main
transport protocol for the methods to be specified is RTP, with payload
as specified in RFC 4103.
Multi-party real-time text requires specific actions for presentation
of the text from the different sources in a way that places the text
from the different sources collected in a clearly readable way while
still also providing an impression of the order in time that text
from the different sources was created. This requirement makes plain
mixing of the text from different sources in a similar way as usually
done for audio unsuitable. Instead, for good presentation, the sender
of the text from different sources need to indicate the source of text
and interleave transmission of text from the different sources to let
the receiver have control over the presentation.
Indication of source of each T.140 text item, and interleaved
transmission of text from different sources can be done in a number
of different ways. Four ways have been identified and discussed:
Use of the RTP translator specified in RFC 3550, use of RTP bundle
specified in RFC 8108, using separate RTP sessions (or data channels)
for each source and finally; including a source in the T.140 text stream
as a new T.140 control code. The most realistic ways are studied
during the work and their benefits and weaknesses are described.
One method is selected to be recommended and specified in more
detail. Ways to negotiate the recommended mixing method will be
specified.
Many current implementations of Real-time text have no multi-party
capability and no conference-awareness. In order to enable participation
in multi-party sessions also for such implementations, a form of limited
multi-party presentation arranged by a specific mixer function for this
case will be specified. The presentation for this case cannot be
expected to have good usability, but will rather be a low
functionality fallback method.
Input material to the work, is an expired IETF draft:
"Text media handling in RTP based real-time conferences"
https://tools.ietf.org/html/draft-hellstrom-text-conference-04
and a specification available in the real-time text task force:
"Multi-party real-time text for presentation in conference-unaware user agents"
http://www.realtimetext.org/sites/default/files/Files_and_Documents/Specifications/multiparty-real-time-text-mixer-2011-04-30.pdf
Aspects to consider for presentation of real-time text is found in an expired
IETF draft "Presentation of Text Conversation in real-time and en-bloc form".
https://datatracker.ietf.org/doc/draft-hellstrom-textpreview/
The work will focus on use in the SIP RFC 3261 call control environment.
Opportunities to use the methods or variants of them in WebRTC
will be mentioned.
The goal is that the fully specified method will be applicable in the
next generation emergency services as specified in RFC 6443, and in 3GPP IMS.
The methods used for multi-party call control and specified in RFC 4579
and RFC 4575 will be among the ones studied.
The expected output is one Best Current Practices document specifying
recommended use of standards for the purpose, and, if needed, a short
Standard Track documents registering items for capability declarations
and negotiating the recommended method.
The main document may also specify need for extensions on the ITU-T T.140
protocol.