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Re: Fwd: RTT note in WebRTC 1.0

From: Janina Sajka <janina@rednote.net>
Date: Wed, 9 Oct 2019 05:58:22 -0400
To: Judy Brewer <jbrewer@w3.org>
Cc: RQTF <public-rqtf@w3.org>, Dominique Hazael-Massieux <dom@w3.org>
Message-ID: <20191009095822.GC2423@rednote.net>
Hello All:

I have revised Dom's text somewhat and included suggested language from
Josh. Before we send this out to APA for approval, can we please
determine I have improved the language--and not impaired it!

Accessibility considerations [New section, informative]

The WebRTC 1.0 specification exposes an API to control protocols
(defined within the IETF) necessary to establish real-time
audio, video and data exchange.

Real-time Text, defined in RFC 4103 on which people
who are deaf or hard of hearing (among others) rely on for their communication needs, utilizes T.140
encapsulated in RTP to enable the transition from TDD/TTY devices to
IP-based communications. Support for RFC 4103 is especially important is it is
being established as the new and more reliable mechanism for text
communications with emergency service centers.

Since Real-time Text requires the ability to send and receive data in near
real time, it can be best supported via the WebRTC 1.0 data channel API. As
defined by the IETF, the data channel protocol utilizes the SCTP/DTLS/UDP
protocol stack, which supports both reliable and unreliable data channels. The
IETF chose to standardize SCTP/DTLS/UDP over proposals for an RTP data channel
which relied on SRTP key management and were focused on unreliable

Since the IETF chose a different approach than the RTP data channel as part of
the WebRTC suite of protocols, as of the time of this publication there is no
standardized way for the WebRTC APIs to directly support Real-time Text as
defined at IETF and implemented in U.S. (FCC) regulations.  The WebRTC working
group will be actively looking to address this gap in future specification
revisions, as well as at progressing technical API requirements.  We hope to
do this in conjunction with developing IETF protocols.

Within the IETF MMUSIC WG, work is ongoing to enable Real-time text to
be sent over the WebRTC data channel, allowing gateways to be deployed
to translate between the SCTP data channel protocol and RFC 4103
Real-time text. This work, once completed, would enable a unified and
interoperable approach for integrating real-time text in WebRTC
user-agents (including browsers) - through a gateway or otherwise.


As of this publication polyfill implementations exist that do enable
effective RTT support in WebRTC applications. This is deemed sufficient until
such time as future
gateways are enabled via IETF protocols such as the SCTP data channel protocol
and RFC 4103 Real-time text. This will need to be defined at IETF in
conjunction with related work at W3C groups to effectively and consistently standardise RTT
support internationally.




Janina Sajka

Linux Foundation Fellow
Executive Chair, Accessibility Workgroup:	http://a11y.org

The World Wide Web Consortium (W3C), Web Accessibility Initiative (WAI)
Chair, Accessible Platform Architectures	http://www.w3.org/wai/apa
Received on Wednesday, 9 October 2019 09:58:25 UTC

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