draft-holmberg-mmusic-t140-usage-data-channel-01.txt   draft-holmberg-mmusic-t140-usage-data-channel-02.txt 
MMUSIC Working Group C. Holmberg MMUSIC Working Group C. Holmberg
Internet-Draft Ericsson Internet-Draft Ericsson
Updates: RFC8373 (if approved) August 29, 2019 Updates: RFC8373 (if approved) September 3, 2019
Intended status: Standards Track Intended status: Standards Track
Expires: March 1, 2020 Expires: March 6, 2020
T.140 Real-time Text Conversation over WebRTC Data Channels T.140 Real-time Text Conversation over WebRTC Data Channels
draft-holmberg-mmusic-t140-usage-data-channel-01 draft-holmberg-mmusic-t140-usage-data-channel-02
Abstract Abstract
This document specifies how a WebRTC data channel can be used as a 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 transport mechanism for Real-time text using the ITU-T Protocol for
multimedia application text conversation (Recommendation ITU-T multimedia application text conversation (Recommendation ITU-T
T.140), and how the SDP offer/answer mechanism can be used to T.140), and how the SDP offer/answer mechanism can be used to
negotiate such data channel, referred to as T.140 data channel. negotiate such data channel, referred to as T.140 data channel.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 1, 2020. This Internet-Draft will expire on March 6, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SDP Considerations . . . . . . . . . . . . . . . . . . . . . 3 3. SDP Considerations . . . . . . . . . . . . . . . . . . . . . 3
3.1. Use of dcmap Attribute . . . . . . . . . . . . . . . . . 3 3.1. Use of dcmap Attribute . . . . . . . . . . . . . . . . . 3
3.2. Use of dcsa Attribute . . . . . . . . . . . . . . . . . . 4 3.2. Use of dcsa Attribute . . . . . . . . . . . . . . . . . . 4
3.2.1. Maximum Character Transmission . . . . . . . . . . . 4 3.2.1. Maximum Character Transmission . . . . . . . . . . . 4
3.2.2. Real-time Text Conversation Languages . . . . . . . . 4 3.2.2. Real-time Text Conversation Languages . . . . . . . . 5
3.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 5 3.2.3. Real-time Text Direction . . . . . . . . . . . . . . 5
4. T.140 Considerations . . . . . . . . . . . . . . . . . . . . 6 3.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Session Layer Functions . . . . . . . . . . . . . . . . . 6 4. T.140 Considerations . . . . . . . . . . . . . . . . . . . . 8
4.2. Data Encoding and Sending . . . . . . . . . . . . . . . . 6 4.1. Session Layer Functions . . . . . . . . . . . . . . . . . 8
4.3. Data Buffering . . . . . . . . . . . . . . . . . . . . . 6 4.2. Data Encoding and Sending . . . . . . . . . . . . . . . . 9
4.4. Loss of T140blocks . . . . . . . . . . . . . . . . . . . 7 4.3. Data Buffering . . . . . . . . . . . . . . . . . . . . . 9
4.5. Multi-party Considerations . . . . . . . . . . . . . . . 7 4.4. Loss of T140blocks . . . . . . . . . . . . . . . . . . . 9
5. Gateway Considerations . . . . . . . . . . . . . . . . . . . 7 4.5. Multi-party Considerations . . . . . . . . . . . . . . . 10
6. Update to RFC 8373 . . . . . . . . . . . . . . . . . . . . . 9 5. Gateway Considerations . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. Update to RFC 8373 . . . . . . . . . . . . . . . . . . . . . 11
8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 8. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 8.1. Subprotocol Identifier t140 . . . . . . . . . . . . . . . 12
10.1. Normative References . . . . . . . . . . . . . . . . . . 10 8.2. SDP fmtp Attribute . . . . . . . . . . . . . . . . . . . 12
10.2. Informative References . . . . . . . . . . . . . . . . . 11 8.3. SDP Language Attributes . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11 8.4. SDP Media Direction Attributes . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . 16
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
The ITU-T Protocol for multimedia application text conversation The ITU-T Protocol for multimedia application text conversation
(Recommendation ITU-T T.140) [T140] defines a protocol for text (Recommendation ITU-T T.140) [T140] defines a protocol for text
conversation, also known as real-time text. The native transport for conversation, also known as real-time text. The native transport for
IP networks is the "RTP Payload for Text Conversation" [RFC4103] IP networks is the "RTP Payload for Text Conversation" [RFC4103]
mechanism, based on the Real-time Transport Protocol (RTP) [RFC4103]. mechanism, based on the Real-time Transport Protocol (RTP) [RFC4103].
This document specifies how a WebRTC data channel This document specifies how a WebRTC data channel
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3.2. Use of dcsa Attribute 3.2. Use of dcsa Attribute
An offerer and answerer MAY, in each offer and answer, include an SDP An offerer and answerer MAY, in each offer and answer, include an SDP
'dcsa' attribute [I-D.ietf-mmusic-data-channel-sdpneg] in the m= 'dcsa' attribute [I-D.ietf-mmusic-data-channel-sdpneg] in the m=
section describing the SCTP association used to realize the T.140 section describing the SCTP association used to realize the T.140
data channel. data channel.
3.2.1. Maximum Character Transmission 3.2.1. Maximum Character Transmission
A 'dcsa' attribute can contain the SDP fmtp attribute used to A 'dcsa' attribute can contain the SDP 'fmtp' attribute used to
indicate a maximum character transmission rate [RFC4103]. The 'cps' indicate a maximum character transmission rate [RFC4103]. The 'cps'
attribute parameter is used indicate the maximum character attribute parameter is used indicate the maximum character
transmission rate that the endpoint that includes the attribute is transmission rate that the endpoint that includes the attribute is
able to receive. The 'format' attribute parameter is not used with able to receive. The 'format' attribute parameter is not used with
T.140 data channels, and MUST be set to "-". T.140 data channels, and MUST be set to "-".
If the fmtp attribute is not included, it indicates that no maximum If the 'fmtp' attribute is not included, it indicates that no maximum
character transmission rate is indicated. It does not mean that the character transmission rate is indicated. It does not mean that the
default value of 30 applies [RFC4103]. default value of 30 applies [RFC4103].
The offerer and answerer MAY modify the 'cps' attribute parameter The offerer and answerer MAY modify the 'cps' attribute parameter
value in subsequent offers and answers. value in subsequent offers and answers.
NOTE: The 'cps' attribute parameter is especially useful when a T.140 NOTE: The 'cps' attribute parameter is especially useful when a T.140
data channel endpoint is acting as a gateway [Section 5] and is data channel endpoint is acting as a gateway [Section 5] and is
interworking with a T.140 transport mechanism that have restrictions interworking with a T.140 transport mechanism that have restrictions
on how many characters can be sent per second. on how many characters can be sent per second.
3.2.2. Real-time Text Conversation Languages 3.2.2. Real-time Text Conversation Languages
'dcsa' attributes can contain the SDP hlang-send and hlang-recv 'dcsa' attributes can contain the SDP 'hlang-send' and 'hlang-recv'
attributes [RFC8373] to negotiate the language to be used for the attributes [RFC8373] to negotiate the language to be used for the
real-time text conversation. real-time text conversation.
For a T.140 data channel, the modality is "written" [RFC8373]. For a T.140 data channel, the modality is "written" [RFC8373].
3.2.3. Real-time Text Direction
'dcsa' attributes can contain the SDP 'sendonly', 'recvonly',
'sendrecv' and 'inactive' attributes [RFC4566] to negotite the
direction in which text can be transmitted in a real-time text
conversation, following the procedures in [RFC3264].
NOTE: A WebRTC data channel is always bi-directional. The usage of
the 'dcsa' attribute only affects the direction in which
implementations are allowed to transmit text on a T.140 data channel.
The offer/answer rules for the direction attributes are based on the
rules for unicast streams defined in [RFC3264], as described below.
Note that the rules only apply to the direction attributes.
NOTE: As for any other attribute included in a 'dcsa' attribute, the
direction attributes only apply to the T.140 data channel for which
the 'dcsa' attribute is used. They have no impact on other data
channels.
Session level direction attributes [RFC4566] have no impact on a
T.140 data channel. An offerer and answerer MUST mark the direction
of the text by sending a direction attribute inside aEUR~dcsa-
attribute.
3.2.3.1. Negotiate Text Direction
3.2.3.1.1. Generating an Offer
If the offerer wishes to both send or receive text on a T.140 data
channel, it SHOULD mark the data channel as sendrecv with a
aEUR~sendrecvaEUR[TM] attribute inside a aEUR~dcsaaEUR[TM] attribute.
If the offerer does not explicitly mark the data channel, a
aEUR~sendrecvaEUR[TM] attribute inside a aEUR~dcsaaEUR[TM] attribute
is implicitly applied.
If the offerer wishes to only send text on a T.140 data channel, it
MUST mark the data channel as sendonly with a aEUR~sendonlyaEUR[TM]
attribute inside a aEUR~dcsaaEUR[TM] attribute.
If the offerer wishes to only receive text on a T.140 data channel,
it MUST mark the data channel as recvonly with a
aEUR~recvonlyaEUR[TM] attribute inside a aEUR~dcsaaEUR[TM] attribute.
If the offerer wishes to neither send or receive text on a T.140 data
channel, it MUST mark the data channel as inactive with a
aEUR~inactiveaEUR[TM] attribute inside a aEUR~dcsaaEUR[TM] attribute.
If the offerer has marked a data channel as sendrecv (implicit or
explicit) or recvonly, it MUST be prepared to receive T.140 data as
soon as the state of the T.140 data channel allows it.
When the offerer receives an answer to the offer, if the answerer has
marked a data channel as sendrecv (implicit or explicit) or recvonly
in the answer, the offerer can start to send T.140 data as soon as
the state of the T.140 data channel allows it. If the answerer has
marked the data channel as inactive or sendonly, the offerer MUST NOT
send any T.140 data.
3.2.3.1.2. Generating an Answer
When the answerer accepts an offer, and marks the direction of the
text in the corresponding answer, the marking is based on the marking
(explicit or implicit) in the offer.
If the offerer marked the data channel as sendrecv (implicitly or
explicitly), the answerer MUST mark the data channel as sendrecv,
sendonly, recvonly or inactive with a aEUR~sendrecvaEUR[TM],
aEUR~sendonlyaEUR[TM], aEUR~recvonlyaEUR[TM] respective
aEUR~inactiveaEUR[TM] attribute inside a aEUR~dcsaaEUR[TM] attribute.
If the answerer does not explicitly mark the data channel, a
aEUR~sendrecvaEUR[TM] attribute inside a aEUR~dcsaaEUR[TM] attribute
is implicitly applied.
If the offerer marked the data channel as sendonly, the answerer MUST
mark the data channel as recvonly or inactive with a
aEUR~recvonlyaEUR[TM] respective aEUR~inactiveaEUR[TM] attribute
inside a aEUR~dcsaaEUR[TM] attribute.
If the offerer marked the data channel as recvonly, the answerer MUST
mark the data channel as sendonly or inactive with a
aEUR~sendonlyaEUR[TM] respective aEUR~inactiveaEUR[TM] attribute
inside a aEUR~dcsaaEUR[TM] attribute.
If the offerer marked the data channel as inactive, the answerer MUST
mark the data channel as inactive with a aEUR~inactiveaEUR[TM]
attribute inside a aEUR~dcsaaEUR[TM] attribute.
If the answerer has marked a data channel as sendrecv or recvonly, it
MUST be prepared to receive data as soon as the state of the T.140
data channel allows transmission of data.
3.2.3.2. Modify Text Direction
If an endpoint wishes to modify a previously negotiated text
direction in an ongoing session, it MUST initiate an offer that
indicates the new direction, following the rules in
Section 3.2.3.1.1. If the answerer accepts the offer it follows the
procedures in Section 3.2.3.1.2.
3.3. Examples 3.3. Examples
Below is an example of an m= section describing a T.140 data channel, Below is an example of an m= section describing a T.140 data channel,
where the maximum character transmission rate is set to 20. where the maximum character transmission rate is set to 20, and the
text transmission direction is set to "sendrecv".
m=application 911 UDP/DTLS/SCTP webrtc-datachannel m=application 911 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 2001:db8::3 c=IN IP6 2001:db8::3
a=max-message-size:1000 a=max-message-size:1000
a=sctp-port 5000 a=sctp-port 5000
a=dcmap:1 label="text conversation";subprotocol="t140" a=dcmap:1 label="text conversation";subprotocol="t140"
a=dcsa:1 fmtp:- cps=20 a=dcsa:1 fmtp:- cps=20
a=dcsa:1 sendrecv
Below is an example of an m= section of an offer for a T.140 data Below is an example of an m= section of an offer for a T.140 data
channel offering real-time text conversation in Spanish and channel offering real-time text conversation in Spanish and
Esperanto, and an m= section in the associated answer accepting Esperanto, and an m= section in the associated answer accepting
Esperanto. Esperanto.
Offer: Offer:
m=application 911 UDP/DTLS/SCTP webrtc-datachannel m=application 911 UDP/DTLS/SCTP webrtc-datachannel
c=IN IP6 2001:db8::3 c=IN IP6 2001:db8::3
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(Section 3.2), if such has been provided by the peer. (Section 3.2), if such has been provided by the peer.
An implementation needs to take the user requirements for smooth flow An implementation needs to take the user requirements for smooth flow
and low latency in real-time text conversation into consideration and low latency in real-time text conversation into consideration
when assigning a buffer time. It is RECOMMENDED to use the default when assigning a buffer time. It is RECOMMENDED to use the default
transmission interval of 300 milliseconds [RFC4103], or lower, also transmission interval of 300 milliseconds [RFC4103], or lower, also
for T.140 data channels. for T.140 data channels.
4.4. Loss of T140blocks 4.4. Loss of T140blocks
In case of network failure or congestion, T140 data channels might In case of network failure or congestion, T.140 data channels might
fail and get torn down. If this happens but the session sustains, it fail and get torn down. If this happens but the session sustains, it
is RECOMMENDED that a low number of retries are made to reestablish is RECOMMENDED that a low number of retries are made to reestablish
the T140 data channels. If reestablishment of the T140 data channel the T.140 data channels. If reestablishment of the T.140 data
is successful, an implementation MUST evaluate if any T140blocks were channel is successful, an implementation MUST evaluate if any
lost. Retransmission of already transmitted T140blocks MUST be T140blocks were lost. Retransmission of already transmitted
avoided, and missing text markers [T140ad1] SHOULD be inserted in the T140blocks MUST be avoided, and missing text markers [T140ad1] SHOULD
received data stream where loss is detected or suspected. be inserted in the received data stream where loss is detected or
suspected.
An implementation needs to take the user requirements for smooth flow An implementation needs to take the user requirements for smooth flow
and low latency in real-time text conversation into consideration and low latency in real-time text conversation into consideration
when assigning a buffer time. It is RECOMMENDED to use the default when assigning a buffer time. It is RECOMMENDED to use the default
transmission interval of 300 milliseconds [RFC4103], or lower, also transmission interval of 300 milliseconds [RFC4103], or lower, also
for T.140 data channels. for T.140 data channels.
4.5. Multi-party Considerations 4.5. Multi-party Considerations
If an implementation needs to support multi-party scenarios, the If an implementation needs to support multi-party scenarios, the
implementation needs to support multiple simultaneous T.140 data implementation needs to support multiple simultaneous T.140 data
channels, one for each remote party. At the time of writing this channels, one for each remote party. At the time of writing this
document, this is true even in scenarios where each participants document, this is true even in scenarios where each participant
communicate via a centralized conference server. The reason is that, communicate via a centralized conference server. The reason is that,
unlike RTP media, WebRTC data channels and the T.140 protocol do not unlike RTP media, WebRTC data channels and the T.140 protocol do not
support the indication of the source of T.140 data. The SDP 'dcmap' support the indication of the source of T.140 data. The SDP 'dcmap'
attribute label attribute parameter (Section 3.1) can be used by the attribute label attribute parameter (Section 3.1) can be used by the
offerer to provide additional information about each T.140 data offerer to provide additional information about each T.140 data
channel, and help implementations to distinguish between them. channel, and help implementations to distinguish between them.
NOTE: Future extensions to T.140, or to the T140block, might allow NOTE: Future extensions to T.140, or to the T140block, might allow
indicating the source of T.140 data, in which case it might be indicating the source of T.140 data, in which case it might be
possible to use a single T.140 data channel to transport data from possible to use a single T.140 data channel to transport data from
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are no longer used, as the technologies they use have been obsoleted are no longer used, as the technologies they use have been obsoleted
etc, while others are still in use. etc, while others are still in use.
When performing interworking between T.140 data channels and another When performing interworking between T.140 data channels and another
real-time text transports and protocols with real-time text in real-time text transports and protocols with real-time text in
another, a number of factors need to be considered. At the time of another, a number of factors need to be considered. At the time of
writing this document, the most common IP-based real-time text writing this document, the most common IP-based real-time text
transport is the RTP based mechanism defined in [RFC4103]. While transport is the RTP based mechanism defined in [RFC4103]. While
this document does not define a complete interworking solution, this this document does not define a complete interworking solution, this
list below provides some guidance and considerations to take into list below provides some guidance and considerations to take into
account when designing an gateway for interworking between T140 data account when designing an gateway for interworking between T.140 data
channels and RTP-based T.140 transport: channels and RTP-based T.140 transport:
o For each T.140 data channel there is an RTP stream for real-time o For each T.140 data channel there is an RTP stream for real-time
text [RFC4103] . Redundancy is by default declared and used on text [RFC4103] . Redundancy is by default declared and used on
RTP stream. On the T.140 data channel there is no redundancy, but RTP stream. On the T.140 data channel there is no redundancy, but
the reliable property [I-D.ietf-mmusic-data-channel-sdpneg] of the reliable property [I-D.ietf-mmusic-data-channel-sdpneg] of
T.140 the data channel is set. T.140 the data channel is set.
o During a normal text flow, T140blocks received from one network o During a normal text flow, T140blocks received from one network
are forwarded towards the other network. Keep-alive traffic is are forwarded towards the other network. Keep-alive traffic is
implicit on the T.140 data channel. A gateway might have to implicit on the T.140 data channel. A gateway might have to
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o For each T.140 data channel there is an RTP stream for real-time o For each T.140 data channel there is an RTP stream for real-time
text [RFC4103] . Redundancy is by default declared and used on text [RFC4103] . Redundancy is by default declared and used on
RTP stream. On the T.140 data channel there is no redundancy, but RTP stream. On the T.140 data channel there is no redundancy, but
the reliable property [I-D.ietf-mmusic-data-channel-sdpneg] of the reliable property [I-D.ietf-mmusic-data-channel-sdpneg] of
T.140 the data channel is set. T.140 the data channel is set.
o During a normal text flow, T140blocks received from one network o During a normal text flow, T140blocks received from one network
are forwarded towards the other network. Keep-alive traffic is are forwarded towards the other network. Keep-alive traffic is
implicit on the T.140 data channel. A gateway might have to implicit on the T.140 data channel. A gateway might have to
extract keep-alives from incoming RTP streams, and MAY generate extract keep-alives from incoming RTP streams, and MAY generate
keep-alives on outgoing RTP streams. keep-alives on outgoing RTP streams.
o It is RECOMMENDED that the gateway uses the same transmission o It is RECOMMENDED that the gateway uses the same transmission
interval on both the T140 data channel and the RTP stream, if interval on both the T.140 data channel and the RTP stream, if
possible. That will reduce the delay caused by buffering. possible. That will reduce the delay caused by buffering.
o If the gateway detects or suspects loss of data on the RTP stream, o If the gateway detects or suspects loss of data on the RTP stream,
the gateway gateway SHOULD insert the T.140 missing text marker the gateway gateway SHOULD insert the T.140 missing text marker
[T140ad1] in the data sent on the outgoing T.140 data channel. [T140ad1] in the data sent on the outgoing T.140 data channel.
o If the gateway detects or suspects loss of data on the T.140 data o If the gateway detects or suspects loss of data on the T.140 data
channel, the gateway gateway SHOULD insert the T.140 missing text channel, the gateway gateway SHOULD insert the T.140 missing text
marker [T140ad1] in the data sent on the outgoing RTP stream. marker [T140ad1] in the data sent on the outgoing RTP stream.
o If the gateway detects that the T.140 data channel has failed and o If the gateway detects that the T.140 data channel has failed and
got torn down, once the data channel has been reestablished the got torn down, once the data channel has been reestablished the
gateway SHOULD insert the T.140 missing text marker [T140ad1] in gateway SHOULD insert the T.140 missing text marker [T140ad1] in
the data sent on the outgoing RTP stream. the data sent on the outgoing RTP stream if it detects or suspects
that data on the T.140 data channel was lost.
o The gateway MUST indicate the same text transmission direction
(Section 3.2.3) on the T.140 data channel and the RTP stream.
NOTE: In order for the gateway to insert a missing text marker, or to NOTE: In order for the gateway to insert a missing text marker, or to
perform other actions that require that the gateway has access to the perform other actions that require that the gateway has access to the
T.140 data, the T.140 data cannot be encrypted end-to-end between the T.140 data, the T.140 data cannot be encrypted end-to-end between the
T.140 data channel endpoint and the RTP endpoint. At the time of T.140 data channel endpoint and the RTP endpoint. At the time of
writing this document, a mechanism to provide such end-to-end writing this document, a mechanism to provide such end-to-end
encryption has not been defined. encryption has not been defined.
6. Update to RFC 8373 6. Update to RFC 8373
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The generic security considerations for the SDP-based external The generic security considerations for the SDP-based external
negotiation method are defined in negotiation method are defined in
[I-D.ietf-mmusic-data-channel-sdpneg]. [I-D.ietf-mmusic-data-channel-sdpneg].
8. IANA considerations 8. IANA considerations
[RFC EDITOR NOTE: Please replace all instances of RFCXXXX with the [RFC EDITOR NOTE: Please replace all instances of RFCXXXX with the
RFC number of this document.] RFC number of this document.]
8.1. Subprotocol Identifier t140
This document adds the subprotocol identifier "t140" to the This document adds the subprotocol identifier "t140" to the
"WebSocket Subprotocol Name Registry" as follows: "WebSocket Subprotocol Name Registry" as follows:
+--------------------------+-------------+ +--------------------------+-------------+
| Subprotocol Identifier: | t140 | | Subprotocol Identifier: | t140 |
| Subprotocol Common Name: | ITU-T T.140 | | Subprotocol Common Name: | ITU-T T.140 |
| Subprotocol Definition: | RFCXXXX | | Subprotocol Definition: | RFCXXXX |
| Reference: | RFCXXXX | | Reference: | RFCXXXX |
+--------------------------+-------------+ +--------------------------+-------------+
8.2. SDP fmtp Attribute
This document modifies the usage of the SDP 'fmtp' attribute, if this
attribute is included in an SDP 'dcsa' attribute and associated with
an T.140 real-time text session over a WebRTC data channel. The
modified usage is described in Section 3.2.1.
The usage level "dcsa(t140)" is added to the IANA registration of the
SDP 'fmtp' attribute as follows:
+-----------------------+-------------------------------------------+
| Contact name: | MMUSIC Chairs |
| Contact email: | mmusic-chairs@ietf.org |
| Attribute name: | fmtp |
| Usage level: | dcsa(t140) |
| Purpose: | Indicate the maximum transmission rate |
| | that an endpoint is willing to recive on |
| | a T.140 data channel. |
| Reference: | RFCXXXX |
+-----------------------+-------------------------------------------+
8.3. SDP Language Attributes
This document modifies the usage of the SDP 'hlang-send' and 'hlang-
recv' attributes, if these attributes are included in SDP 'dcsa'
attributes associated with an T.140 data channel. The modified usage
is described in Section 3.2.2.
The usage level "dcsa(t140)" is added to the IANA registration of the
SDP 'hlang-send' attribute as follows:
+-----------------------+-------------------------------------------+
| Contact name: | MMUSIC Chairs |
| Contact email: | mmusic-chairs@ietf.org |
| Attribute name: | hlang-send |
| Usage level: | dcsa(t140) |
| Purpose: | Negotiate the language to be used on a |
| | T.140 data channel. |
| Reference: | RFCXXXX |
+-----------------------+-------------------------------------------+
The usage level "dcsa(t140)" is added to the IANA registration of the
SDP 'hlang-recv' attribute as follows:
+-----------------------+-------------------------------------------+
| Contact name: | MMUSIC Chairs |
| Contact email: | mmusic-chairs@ietf.org |
| Attribute name: | hlang-recv |
| Usage level: | dcsa(t140) |
| Purpose: | Negotiate the language to be used on a |
| | T.140 data channel. |
| Reference: | RFCXXXX |
+-----------------------+-------------------------------------------+
8.4. SDP Media Direction Attributes
This document modifies the usage of the SDP 'sendonly', 'recvonly',
'sendrecv' and 'inactive' attributes, if these attributes are
included in SDP 'dcsa' attributes associated T.140 data channel. The
modified usage is described in Section 3.2.3.
The usage level "dcsa(t140)" is added to the IANA registration of the
SDP 'sendonly' attribute as follows:
+-----------------------+-------------------------------------------+
| Contact name: | MMUSIC Chairs |
| Contact email: | mmusic-chairs@ietf.org |
| Attribute name: | sendonly |
| Usage level: | dcsa(t140) |
| Purpose: | Negotiate the direction in which real- |
| | time text can be sent on a T.140 data |
| | channel. |
| Reference: | RFCXXXX |
+-----------------------+-------------------------------------------+
The usage level "dcsa(t140)" is added to the IANA registration of the
SDP 'recvonly' attribute as follows:
+-----------------------+-------------------------------------------+
| Contact name: | MMUSIC Chairs |
| Contact email: | mmusic-chairs@ietf.org |
| Attribute name: | recvonly |
| Usage level: | dcsa(t140) |
| Purpose: | Negotiate the direction in which real- |
| | time text can be sent on a T.140 data |
| | channel. |
| Reference: | RFCXXXX |
+-----------------------+-------------------------------------------+
The usage level "dcsa(t140)" is added to the IANA registration of the
SDP 'sendrecv' attribute as follows:
+-----------------------+-------------------------------------------+
| Contact name: | MMUSIC Chairs |
| Contact email: | mmusic-chairs@ietf.org |
| Attribute name: | sendrecv |
| Usage level: | dcsa(t140) |
| Purpose: | Negotiate the direction in which real- |
| | time text can be sent on a T.140 data |
| | channel. |
| Reference: | RFCXXXX |
+-----------------------+-------------------------------------------+
The usage level "dcsa(t140)" is added to the IANA registration of the
SDP 'inactive' attribute as follows:
+-----------------------+-------------------------------------------+
| Contact name: | MMUSIC Chairs |
| Contact email: | mmusic-chairs@ietf.org |
| Attribute name: | inactive |
| Usage level: | dcsa(t140) |
| Purpose: | Negotiate the direction in which real- |
| | time text can be sent on a T.140 data |
| | channel. |
| Reference: | RFCXXXX |
+-----------------------+-------------------------------------------+
9. Acknowledgements 9. Acknowledgements
This document is based on an earlier Internet draft edited by Keith This document is based on an earlier Internet draft edited by Keith
Drage, Juergen Stoetzer-Bradler and Albrecht Schwarz. Drage, Juergen Stoetzer-Bradler and Albrecht Schwarz.
Thomas Belling provided useful comments on the initial (pre- Thomas Belling provided useful comments on the initial (pre-
submission) version of the draft. Gunnar Hellstrom provided comments submission) version of the draft. Gunnar Hellstrom provided comments
and text on the draft. and text on the draft.
10. References 10. References
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