T.140 Real-time Text Conversation over WebRTC Data Channels
draft-ietf-mmusic-t140-usage-data-channel-14
MMUSIC Working Group C. Holmberg
Internet-Draft Ericsson
Updates: 8373 (if approved) G. Hellstrom
Intended status: Standards TrackGunnar Hellstrom Accessible Communicatio
Expires: October 12, 2020 April 10, 2020
T.140 Real-time Text Conversation over WebRTC Data Channels
draft-ietf-mmusic-t140-usage-data-channel-14
Abstract
This document specifies how a WebRTC data channel can be used as a
transport mechanism for Real-time text using the ITU-T Protocol for
multimedia application text conversation (Recommendation ITU-T
T.140), and how the SDP offer/answer mechanism can be used to
negotiate such data channel, referred to as T.140 data channel. This
document updates RFC 8373 to specify its use with WebRTC data
channels.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. WebRTC Data Channel Considerations . . . . . . . . . . . . . 4
4. SDP Considerations . . . . . . . . . . . . . . . . . . . . . 4
4.1. Use of dcmap Attribute . . . . . . . . . . . . . . . . . 4
4.2. Use of dcsa Attribute . . . . . . . . . . . . . . . . . . 5
4.2.1. Maximum Character Transmission Rate . . . . . . . . . 5
4.2.2. Real-time Text Conversation Languages . . . . . . . . 6
4.2.3. Real-time Text Direction . . . . . . . . . . . . . . 7
4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 9
5. T.140 Considerations . . . . . . . . . . . . . . . . . . . . 10
5.1. Session Layer Functions . . . . . . . . . . . . . . . . . 10
5.2. Data Encoding and Sending . . . . . . . . . . . . . . . . 11
5.3. Data Buffering . . . . . . . . . . . . . . . . . . . . . 11
5.4. Loss of T140blocks . . . . . . . . . . . . . . . . . . . 11
5.5. Multi-party Considerations . . . . . . . . . . . . . . . 12
6. Gateway Considerations . . . . . . . . . . . . . . . . . . . 12
7. Update to RFC 8373 . . . . . . . . . . . . . . . . . . . . . 13
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14
9. IANA considerations . . . . . . . . . . . . . . . . . . . . . 14
9.1. Subprotocol Identifier t140 . . . . . . . . . . . . . . . 14
9.2. SDP fmtp Attribute . . . . . . . . . . . . . . . . . . . 15
9.3. SDP Language Attributes . . . . . . . . . . . . . . . . . 15
9.4. SDP Media Direction Attributes . . . . . . . . . . . . . 16
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The ITU-T Protocol for multimedia application text conversation
(Recommendation ITU-T T.140) [T140] defines a protocol for text
conversation, also known as real-time text. The transport used for
IP networks is the "RTP Payload for Text Conversation" [RFC4103]
mechanism, based on the Real-time Transport Protocol (RTP) [RFC3550].
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