draft-ietf-avtcore-multi-party-rtt-mix-02.txt   draft-ietf-avtcore-multi-party-rtt-mix-03.txt 
AVTCore G. Hellstrom AVTCore G. Hellstrom
Internet-Draft Gunnar Hellstrom Accessible Communication Internet-Draft Gunnar Hellstrom Accessible Communication
Updates: RFC 4102, RFC 4103 (if approved) 20 May 2020 Updates: RFC 4102, RFC 4103 (if approved) 27 May 2020
Intended status: Standards Track Intended status: Standards Track
Expires: 21 November 2020 Expires: 28 November 2020
RTP-mixer formatting of multi-party Real-time text RTP-mixer formatting of multi-party Real-time text
draft-ietf-avtcore-multi-party-rtt-mix-02 draft-ietf-avtcore-multi-party-rtt-mix-03
Abstract Abstract
Real-time text mixers for multi-party sessions need to identify the Real-time text mixers for multi-party sessions need to identify the
source of each transmitted group of text so that the text can be source of each transmitted group of text so that the text can be
presented by endpoints in suitable grouping with other text from the presented by endpoints in suitable grouping with other text from the
same source. same source.
Regional regulatory requirements specify provision of real-time text Regional regulatory requirements specify provision of real-time text
in multi-party calls. RFC 4103 mixer implementations can use in multi-party calls. RFC 4103 mixer implementations can use
skipping to change at page 2, line 10 skipping to change at page 2, line 10
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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 21 November 2020. This Internet-Draft will expire on 28 November 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Selected solution and considered alternative . . . . . . 4 1.1. Selected solution and considered alternative . . . . . . 4
1.2. Nomenclature . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Nomenclature . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Intended application . . . . . . . . . . . . . . . . . . 5 1.3. Intended application . . . . . . . . . . . . . . . . . . 5
2. Use of fields in the RTP packets . . . . . . . . . . . . . . 5 2. Use of fields in the RTP packets . . . . . . . . . . . . . . 5
3. Actions at transmission by a mixer . . . . . . . . . . . . . 8 3. Actions at transmission by a mixer . . . . . . . . . . . . . 8
4. Actions at reception . . . . . . . . . . . . . . . . . . . . 10 4. Actions at reception . . . . . . . . . . . . . . . . . . . . 11
5. RTCP considerations . . . . . . . . . . . . . . . . . . . . . 11 5. RTCP considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Chained operation . . . . . . . . . . . . . . . . . . . . . . 11 6. Chained operation . . . . . . . . . . . . . . . . . . . . . . 12
7. Usage without redundancy . . . . . . . . . . . . . . . . . . 12 7. Usage without redundancy . . . . . . . . . . . . . . . . . . 12
8. Use with SIP centralized conferencing framework . . . . . . . 12 8. Use with SIP centralized conferencing framework . . . . . . . 13
9. Media Subtype Registration . . . . . . . . . . . . . . . . . 12 9. Conference control . . . . . . . . . . . . . . . . . . . . . 13
10. SDP considerations . . . . . . . . . . . . . . . . . . . . . 14 10. Media Subtype Registration . . . . . . . . . . . . . . . . . 13
10.1. Security for session control and media . . . . . . . . . 14 11. SDP considerations . . . . . . . . . . . . . . . . . . . . . 14
10.2. SDP offer/answer examples . . . . . . . . . . . . . . . 14 11.1. Security for session control and media . . . . . . . . . 15
11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 16 11.2. SDP offer/answer examples . . . . . . . . . . . . . . . 15
12. Performance considerations . . . . . . . . . . . . . . . . . 19 12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17
13. Presentation level considerations . . . . . . . . . . . . . . 19 13. Performance considerations . . . . . . . . . . . . . . . . . 20
13.1. Presentation by multi-party aware endpoints . . . . . . 20 14. Presentation level considerations . . . . . . . . . . . . . . 20
13.2. Multi-party mixing for multi-party unaware endpoints . . 22 14.1. Presentation by multi-party aware endpoints . . . . . . 21
14. Gateway Considerations . . . . . . . . . . . . . . . . . . . 27 14.2. Multi-party mixing for multi-party unaware endpoints . . 23
14.1. Gateway considerations with Textphones (e.g. TTYs). . . 28 15. Gateway Considerations . . . . . . . . . . . . . . . . . . . 28
14.2. Gateway considerations with WebRTC. . . . . . . . . . . 28 15.1. Gateway considerations with Textphones (e.g. TTYs). . . 29
15. Updates to RFC 4102 and RFC 4103 . . . . . . . . . . . . . . 29 15.2. Gateway considerations with WebRTC. . . . . . . . . . . 29
16. Congestion considerations . . . . . . . . . . . . . . . . . . 29 16. Updates to RFC 4102 and RFC 4103 . . . . . . . . . . . . . . 30
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 17. Congestion considerations . . . . . . . . . . . . . . . . . . 30
18. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
19. Security Considerations . . . . . . . . . . . . . . . . . . . 29 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30
20. Change history . . . . . . . . . . . . . . . . . . . . . . . 29 20. Security Considerations . . . . . . . . . . . . . . . . . . . 30
20.1. Changes included in 21. Change history . . . . . . . . . . . . . . . . . . . . . . . 30
draft-ietf-avtcore-multi-party-rtt-mix-02 . . . . . . . 30 21.1. Changes included in
20.2. Changes to draft-ietf-avtcore-multi-party-rtt-mix-01 . . 30 draft-ietf-avtcore-multi-party-rtt-mix-03 . . . . . . . 31
20.3. Changes from 21.2. Changes included in
draft-ietf-avtcore-multi-party-rtt-mix-02 . . . . . . . 32
21.3. Changes to draft-ietf-avtcore-multi-party-rtt-mix-01 . . 32
21.4. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-03 to draft-hellstrom-avtcore-multi-party-rtt-source-03 to
draft-ietf-avtcore-multi-party-rtt-mix-00 . . . . . . . 30 draft-ietf-avtcore-multi-party-rtt-mix-00 . . . . . . . 32
20.4. Changes from 21.5. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-02 to draft-hellstrom-avtcore-multi-party-rtt-source-02 to
-03 . . . . . . . . . . . . . . . . . . . . . . . . . . 30 -03 . . . . . . . . . . . . . . . . . . . . . . . . . . 32
20.5. Changes from 21.6. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-01 to draft-hellstrom-avtcore-multi-party-rtt-source-01 to
-02 . . . . . . . . . . . . . . . . . . . . . . . . . . 31 -02 . . . . . . . . . . . . . . . . . . . . . . . . . . 33
20.6. Changes from 21.7. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-00 to draft-hellstrom-avtcore-multi-party-rtt-source-00 to
-01 . . . . . . . . . . . . . . . . . . . . . . . . . . 32 -01 . . . . . . . . . . . . . . . . . . . . . . . . . . 34
21. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 22. References . . . . . . . . . . . . . . . . . . . . . . . . . 34
21.1. Normative References . . . . . . . . . . . . . . . . . . 32 22.1. Normative References . . . . . . . . . . . . . . . . . . 34
21.2. Informative References . . . . . . . . . . . . . . . . . 33 22.2. Informative References . . . . . . . . . . . . . . . . . 35
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 34 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction 1. Introduction
RFC 4103[RFC4103] specifies use of RFC 3550 RTP [RFC3550] for RFC 4103[RFC4103] specifies use of RFC 3550 RTP [RFC3550] for
transmission of real-time text (RTT) and the "text/t140" format. It transmission of real-time text (RTT) and the "text/t140" format. It
also specifies a redundancy format "text/red" for increased also specifies a redundancy format "text/red" for increased
robustness. RFC 4102 [RFC4102] registers the "text/red" format. robustness. RFC 4102 [RFC4102] registers the "text/red" format.
Regional regulatory requirements specify provision of real-time text Regional regulatory requirements specify provision of real-time text
in multi-party calls. in multi-party calls.
Real-time text is usually provided together with audio and sometimes
with video in conversational sessions.
The redundancy scheme enables efficient transmission of redundant The redundancy scheme enables efficient transmission of redundant
text in packets together with new text. However the redundant header text in packets together with new text. However the redundant header
format has no source indicators for the redundant transmissions. An format has no source indicators for the redundant transmissions. An
assumption has had to be made that the redundant parts in a packet assumption has had to be made that the redundant parts in a packet
are from the same source as the new text. The recommended are from the same source as the new text. The recommended
transmission is one new and two redundant generations of text transmission is one new and two redundant generations of text
(T140blocks) in each packet and the recommended transmission interval (T140blocks) in each packet and the recommended transmission interval
is 300 ms. is 300 ms.
A mixer, selecting between text input from different sources and A mixer, selecting between text input from different sources and
skipping to change at page 4, line 19 skipping to change at page 4, line 26
A more efficient source identification scheme requires that each A more efficient source identification scheme requires that each
redundant T140block has its source individually preserved. The redundant T140block has its source individually preserved. The
present specification introduces a source indicator by specific rules present specification introduces a source indicator by specific rules
for populating the CSRC-list and the redundancy header in the RTP- for populating the CSRC-list and the redundancy header in the RTP-
packet. packet.
An extended packet format 'text/rex' is specified for this purpose, An extended packet format 'text/rex' is specified for this purpose,
providing the possibility to include text from up to 16 sources in providing the possibility to include text from up to 16 sources in
each packet in order to enhance mixer source switching performance. each packet in order to enhance mixer source switching performance.
By these extensions, the performance requirements on multi-party
mixing for real-time text are exceeded by the solution in the present
document.
A negotiation mechanism can therefore be based on selection between A negotiation mechanism can therefore be based on selection between
the "text/red" and the "text/rex" media formats for verification that the "text/red" and the "text/rex" media formats for verification that
the receiver is able to handle the multi-party coded stream. the receiver is able to handle the multi-party coded stream.
A fall-back mixing procedure is specified for cases when the A fall-back mixing procedure is specified for cases when the
negotiation results in "text/red" being the only common submedia negotiation results in "text/red" being the only common submedia
format. format.
The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103] by The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103] by
skipping to change at page 4, line 40 skipping to change at page 4, line 50
and more strict rules for the use of redundancy. and more strict rules for the use of redundancy.
1.1. Selected solution and considered alternative 1.1. Selected solution and considered alternative
The mechanism specified in the present document makes use of the RTP The mechanism specified in the present document makes use of the RTP
mixer model specified in RFC3550[RFC3550]. From some points of view, mixer model specified in RFC3550[RFC3550]. From some points of view,
use of the RTP translator model specified in RFC 3550 would be more use of the RTP translator model specified in RFC 3550 would be more
efficient, because then the text packets can pass the translator with efficient, because then the text packets can pass the translator with
only minor modification. However, there may be a lack of support for only minor modification. However, there may be a lack of support for
the translator model in existing RTP implementations, and therefore the translator model in existing RTP implementations, and therefore
the more common RTP-mixer model was selected. the more common RTP-mixer model was selected. The translator model
would also easier cause congestion if many users send text
simultaneously.
1.2. Nomenclature 1.2. Nomenclature
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
The terms SDES, CNAME, NAME, SSRC, CSRC, CSRC list, CC are explained The terms SDES, CNAME, NAME, SSRC, CSRC, CSRC list, CC are explained
in [RFC3550] in [RFC3550]
The term "T140block" is defined in RFC 4103 [RFC4103] to contain one The term "T140block" is defined in RFC 4103 [RFC4103] to contain one
or more T.140 code elements. or more T.140 code elements.
1.3. Intended application 1.3. Intended application
The scheme for identification of source of redundant transmissions is The format for multi-party real-time text is primarily intended for
intended for transmission from entities taking the mixer role in use in transmission between mixers and endpoints in centralised
centralised mixing configurations for RTT. It is intended for mixing configurations. It is also applicable between endpoint as
reception by both endpoints and mixers. well as between mixers.
2. Use of fields in the RTP packets 2. Use of fields in the RTP packets
RFC 4103[RFC4103] specifies use of RFC 3550 RTP[RFC3550], and a RFC 4103[RFC4103] specifies use of RFC 3550 RTP[RFC3550], and a
redundancy format "text/red" for increased robustness of real-time redundancy format "text/red" for increased robustness of real-time
text transmission. The current specification updates RFC text transmission. The current specification updates RFC
4102[RFC4102] and RFC 4103[RFC4103] by introducing a rule for 4102[RFC4102] and RFC 4103[RFC4103] by introducing a rule for
populating and using the CSRC-list in the RTP packet and extending populating and using the CSRC-list in the RTP packet and extending
the redundancy header in order to enhance the performance in multi- the redundancy header in order to enhance the performance in multi-
party RTT sessions. party RTT sessions.
skipping to change at page 5, line 49 skipping to change at page 6, line 22
T140blocks MUST be grouped per source in the packet in "source T140blocks MUST be grouped per source in the packet in "source
groups". The recommended level of redundancy is to use one primary groups". The recommended level of redundancy is to use one primary
and two redundant generations of T140blocks. In some cases, a and two redundant generations of T140blocks. In some cases, a
primary or redundant T140block is empty, but is still represented by primary or redundant T140block is empty, but is still represented by
a member in the redundancy header. a member in the redundancy header.
The CC field SHALL show the number of members in the CSRC list. The CC field SHALL show the number of members in the CSRC list.
The RTP header is followed by one or more source groups of data block The RTP header is followed by one or more source groups of data block
headers: one header for each text block to be included. Each of headers: one header for each text block to be included. Each of
these headers except the last provides the timestamp offset and these headers provides the timestamp offset and length of the
length of the corresponding data block, in addition to the payload corresponding data block, in addition to the payload type number
type number corresponding to the payload format "text/t140". The corresponding to the payload format "text/t140". The data block
data block headers are followed by the data fields carrying headers are followed by the data fields carrying T140blocks from the
T140blocks from the sources. Finally, the most recent T140block (if sources. Finally, the most recent T140block (if any) follows.
any) follows.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F| block PT | timestamp offset | block length | |F| block PT | timestamp offset | block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The bits in the header are specified as follows: The bits in the header are specified as follows:
F: 1 bit First bit in header indicates whether another header block F: 1 bit First bit in header indicates whether another header block
follows. It has value 1 if further header blocks follow, and follows. It has value 1 if further header blocks follow, and
value 0 if this is the last header block. value 0 if this is the last header block.
block PT: 7 bits RTP payload type number for this block, block PT: 7 bits RTP payload type number for this block,
corresponding to the t140 payload type. corresponding to the t140 payload type.
timestamp offset: 14 bits Unsigned offset of timestamp of this block timestamp offset: 14 bits Unsigned offset of timestamp of this block
relative to timestamp given in RTP header. The offset is a time relative to timestamp given in RTP header. The offset is a time
to be subtracted from the current timestamp to determine the to be subtracted from the current timestamp to determine the
timestamp of the data when this block was received to the mixer. timestamp of the data when the latest part of this block was sent
For primary data from a mixer, the resulting time is the time when from the original source. If the timestamp offset would be >15
the data or the youngest part of the data was received by the 000, it is set to 15 000. For redundant data, the resulting time
mixer. For primary data from an endpoint, only one primary data is the time when the data was sent as primary from the original
is included last in the packet. If the timestamp offset would be source. If the value would be >15 000, then it SHALL be set to 15
>15 000, it is set to 15 000. For redundant data, the resulting 000 plus 300 times the redundancy level of the data. The high
time the resulting time is the time when the data was sent as
primary. If the value would be >15 000, then it SHALL be set to
15 000 plus 300 times the redundancy level of the data. The high
values appear only in exceptional cases, e.g. when some data has values appear only in exceptional cases, e.g. when some data has
been held in order to keep the text flow under the cps limit. been held in order to keep the text flow under the cps limit.
block length: 10 bits Length in bytes of the corresponding data block length: 10 bits Length in bytes of the corresponding data
block excluding header. block excluding header.
The last data block is placed last in the packet. The timestamp and The last T140block is placed last in the packet. The header for the
block-length fields are derived from the header of this block, since final block has a zero F bit, and apart from that the same fields as
they may be determined from the RTP header and overall packet length. other data headers.
The header for the final block comprises only a zero F bit, and the
block payload type number information corresponding to the t140
format, a total of 8 bits. This is illustrated in the figure below:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0| Block PT |
+-+-+-+-+-+-+-+-+
This specification departs from section 4 of RFC 2198 [RFC2198] which This specification has a packet format that is similar to that of RFC
2198 [RFC2198] but is different from some aspects. RFC 2198
associates the whole of the CSRC-list with the primary data and associates the whole of the CSRC-list with the primary data and
assumes that the same list applies to reconstructed redundant data. assumes that the same list applies to reconstructed redundant data.
In the present specification a T140block is associated with exactly In the present specification a T140block is associated with exactly
one CSRC list member as described above. Also RFC 2198 [RFC2198] one CSRC list member as described above. Also RFC 2198 [RFC2198]
anticipates infrequent change to CSRCs; implementers should be aware anticipates infrequent change to CSRCs; implementers should be aware
that the order of the CSRC-list according to this specification will that the order of the CSRC-list according to this specification will
vary during transitions between transmission from the mixer of text vary during transitions between transmission from the mixer of text
originated by different participants. originated by different participants. Another difference is that the
last member in the data header area in RFC 2198 [RFC2198] only
contains the payload type number while in the current specification
it has the same format as all other entries in the data header.
The picture below shows a typical 'text/rex' RTP packet with multi- The picture below shows a typical 'text/rex' RTP packet with multi-
party RTT contents and coding according to the present specification. party RTT contents and coding according to the present specification.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|X| CC=3 |M| "REX" PT | RTP sequence number | |V=2|P|X| CC=3 |M| "REX" PT | RTP sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| timestamp of packet creation | | timestamp of packet creation |
skipping to change at page 7, line 47 skipping to change at page 8, line 20
|1| T140 PT |timestamp offset of "B-R2" |"B-R2" block length| |1| T140 PT |timestamp offset of "B-R2" |"B-R2" block length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT |timestamp offset of "B-R1" |"B-R1" block length| |1| T140 PT |timestamp offset of "B-R1" |"B-R1" block length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT | timestamp offset of "B-P" | "B-P" block length| |1| T140 PT | timestamp offset of "B-P" | "B-P" block length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT |timestamp offset of "C-R2" |"C-R2" block length| |1| T140 PT |timestamp offset of "C-R2" |"C-R2" block length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1| T140 PT |timestamp offset of "C-R1" |"C-R1" block length| |1| T140 PT |timestamp offset of "C-R1" |"C-R1" block length|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| T140 PT | "A-R2" T.140 encoded redundant data | |0| T140 PT |timestamp offset of "C-P" |"C-P" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | "A-R1" T.140 encoded redundant data | | | "A-R2" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "A-P" T.140 encoded primary data | | | |"A-R1" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|"A-P" T.140 encoded primary d. | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "B-R2" T.140 encoded redundant data | | | "B-R2" T.140 encoded redundant data | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | "B-R1" T.140 encoded redundant data | | | "B-R1" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "B-P" T.140 encoded primary data | | | "B-P" T.140 encoded primary data | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "C-R2" T.140 encoded redundant data | | | "C-R2" T.140 encoded redundant data | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---------------+
| | "C-R1" T.140 encoded redundant data | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "C-P" T.140 encoded primary data | | "C-R1" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "C-P" T.140 encoded primary data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1:A 'text/rex' packet with text from three sources A, B, C. Figure 1:A 'text/rex' packet with text from three sources A, B, C.
3. Actions at transmission by a mixer 3. Actions at transmission by a mixer
A "text/rex" transmitter is sending packets at least at regular
transmission intervals as long as there is something (new or
redundant T140blocks) to transmit. The default transmission interval
that SHOULD be applied is 300 ms.
As soon as a participant is known to participate in a session and As soon as a participant is known to participate in a session and
being available for text reception, a Unicode BOM character SHALL be being available for text reception, a Unicode BOM character SHALL be
sent to it according to the procedures in the present document. sent to it according to the procedures in the present document. If
the transmitter is a mixer, then the source of this character SHALL
be indicated to be the mixer itself.
After that, the transmitter SHALL send keep-alive traffic to the After that, the transmitter SHALL send keep-alive traffic to the
receivers at regular intervals when no other traffic has occurred receivers at regular intervals when no other traffic has occurred
during that interval if that is decided for the actual connection. during that interval if that is decided for the actual connection.
Recommendations for keep-alive can be found in RFC 6263[RFC6263]. Recommendations for keep-alive can be found in RFC 6263[RFC6263].
For multi-party operation, it is RECOMMENDED that the mixer sends a A "text/rex" transmitter SHOULD send packets distributed in time as
packet to each receiver as soon as text has been received from a long as there is something (new or redundant T140blocks) to transmit.
source as long as the maximum number of characters per second The maximum transmission interval SHOULD then be 300 ms. It is
indicated by the recipient is not exceeded, and also the number of RECOMMENDED to send a packet to a receiver as soon as new text to
packets sent per second to a recipient is kept under a specified that receiver is available, as long as the time after the latest sent
number. This number SHALL be 10 if no other limit is applied for the packet to the same receiver is more than 150 ms, and also the maximum
application. The intention is to keep the latency introduced by the character rate to the receiver is not exceeded. The intention is to
mixer low. keep the latency low while keeping a good protection against text
loss in bursty packet loss conditions.
Text received from a participant SHOULD NOT be included in
transmission to that participant.
The mixer has its own SSRC, and its own RTP sequence number series. The mixer has its own SSRC, and its own RTP sequence number series.
The number of redundant generations of T140blocks to include in A mixer SHALL handle reception and recovery of packet loss, marking
transmitted packets SHALL be deducted from the SDP negotiation. It of possible text loss and deletion of 'BOM' characters from each
SHOULD be set to the minimum of the number declared by the receiver participant before queueing received text for transmission to
and the transmitter. The same number of redundant generations MUST receiving participants.
be used for all sources in the transmissions. The number of
The transmitting party sends redundant repetitions of T140blocks
aleady transmitted in earlier packets. The number of redundant
generations of T140blocks to include in transmitted packets SHALL be
deducted from the SDP negotiation. It SHOULD be set to the minimum
of the number declared by the two parties negotiating a connection.
The same number of redundant generations MUST be used for text from
all sources when it is transmitted to a receiver. The number of
generations sent to a receiver SHALL be the same during the whole generations sent to a receiver SHALL be the same during the whole
session unless it is modified by session renegotiation. session unless it is modified by session renegotiation.
At time of transmission, the mixer SHALL populate the RTP packet with At time of transmission, the mixer SHALL populate the RTP packet with
T140blocks combined from all T140blocks queued for transmission T140blocks combined from all T140blocks queued for transmission
originating from each source as long as this is not in conflict with originating from each source as long as this is not in conflict with
the allowed number of characters per second or the maximum packet the allowed number of characters per second or the maximum packet
size. These T140blocks SHALL be placed in the packet interleaved size. These T140blocks SHALL be placed in the packet interleaved
with redundant T140blocks and new T140blocks from other sources. The with redundant T140blocks and new T140blocks from other sources. The
primary and redundant T140blocks from each source are grouped primary and redundant T140blocks from each source are grouped
skipping to change at page 10, line 7 skipping to change at page 10, line 42
Usually this is the level of redundancy used. If a higher number of Usually this is the level of redundancy used. If a higher number of
redundancy is negotiated, then the procedure SHALL be maintained redundancy is negotiated, then the procedure SHALL be maintained
until all available redundant levels of T140blocks and their sources until all available redundant levels of T140blocks and their sources
are placed in the packet. If a receiver has negotiated a lower are placed in the packet. If a receiver has negotiated a lower
number of text/rex generations, then that level shall be the maximum number of text/rex generations, then that level shall be the maximum
used by the transmitter. used by the transmitter.
The timer offset values are inserted in the redundancy header, with The timer offset values are inserted in the redundancy header, with
the time offset from the RTP timestamp in the packet when the the time offset from the RTP timestamp in the packet when the
corresponding T140block was sent from the mixer as primary. corresponding T140block was sent from its original source as primary.
The number of members in the CSRC list shall be placed in the "CC" The number of members in the CSRC list shall be placed in the "CC"
header field. Only mixers place values >0 in the "CC" field. header field. Only mixers place values >0 in the "CC" field.
When there is no new T140block to transmit, and no redundant When there is no new T140block to transmit, and no redundant
T140block that has not been retransmitted the intended number of T140block that has not been retransmitted the intended number of
times, the transmission process can stop until either new T140blocks times, the transmission process can stop until either new T140blocks
arrive, or a keep-alive method calls for transmission of keep-alive arrive, or a keep-alive method calls for transmission of keep-alive
packets. packets.
skipping to change at page 12, line 15 skipping to change at page 12, line 44
7. Usage without redundancy 7. Usage without redundancy
The "text/rex" format SHALL be used also for multi-party The "text/rex" format SHALL be used also for multi-party
communication when the redundancy mechanism is not used. That MAY be communication when the redundancy mechanism is not used. That MAY be
the case when robustness in transmission is provided by some other the case when robustness in transmission is provided by some other
means than by redundancy. All aspects of the present document SHALL means than by redundancy. All aspects of the present document SHALL
be applied except the redundant generations in transmission. be applied except the redundant generations in transmission.
The "text/rex" format SHOULD thus be used for multi-party operation, The "text/rex" format SHOULD thus be used for multi-party operation,
also when some other protection against packet loss is utilized, for also when some other protection against packet loss is utilized, for
example a reliable network or transport. The format is also allowed example a reliable network or transport. The format is also suitable
to be used for point-to-point operation. to be used for point-to-point operation.
8. Use with SIP centralized conferencing framework 8. Use with SIP centralized conferencing framework
The SIP conferencing framework, mainly specified in RFC The SIP conferencing framework, mainly specified in RFC
4353[RFC4353], RFC 4579[RFC4579] and RFC 4575[RFC4575] is suitable 4353[RFC4353], RFC 4579[RFC4579] and RFC 4575[RFC4575] is suitable
for coordinating sessions including multi-party RTT. The RTT stream for coordinating sessions including multi-party RTT. The RTT stream
between the mixer and a participant is one and the same during the between the mixer and a participant is one and the same during the
conference. Participants get announced by notifications when conference. Participants get announced by notifications when
participants are joining or leaving, and further user information may participants are joining or leaving, and further user information may
skipping to change at page 12, line 38 skipping to change at page 13, line 25
security purposes and for translation to a label for presentation to security purposes and for translation to a label for presentation to
other users. other users.
Note: The CSRC-list in an RTP packet only includes participants who's Note: The CSRC-list in an RTP packet only includes participants who's
text is included in one or more text blocks. It is not the same as text is included in one or more text blocks. It is not the same as
the total list of participants in a conference. With audio and video the total list of participants in a conference. With audio and video
media, the CSRC-list would often contain all participants who are not media, the CSRC-list would often contain all participants who are not
muted whereas text participants that don't type are completely silent muted whereas text participants that don't type are completely silent
and thus are not represented in RTP packet CSRC-lists. and thus are not represented in RTP packet CSRC-lists.
9. Media Subtype Registration 9. Conference control
In managed conferences, control of the real-time text media SHOULD be
provided in the same way as other for media, e.g. for muting and
unmuting by the direction attributes in sdp [RFC4566].
Note that floor control functions may be of value for RTT users as
well as for users of other media in a conference.
10. Media Subtype Registration
This registration is done using the template defined in [RFC6838] and This registration is done using the template defined in [RFC6838] and
following [RFC4855]. following [RFC4855].
Type name: text Type name: text
Subtype name: rex Subtype name: rex
Required parameters: rate: The RTP timestamp (clock) rate. The Required parameters: rate: The RTP timestamp (clock) rate. The
only valid value is 1000. only valid value is 1000.
pt: A slash-separated list with the payload pt: A slash-separated list with the payload
type number(pt) for the primary text, the first redundant text, type number(pt) for the primary text, the first redundant text,
the second redundant text etc, that the receiver is capable to the second redundant text etc, that the receiver is capable to
receive. receive.
Optional parameter: cps: This parameter is used to signal the Optional parameter: cps: This parameter is used to signal the
capabilities of a receiver implementation. It indicates the capabilities of a receiver implementation. It indicates the
skipping to change at page 13, line 19 skipping to change at page 14, line 10
the second redundant text etc, that the receiver is capable to the second redundant text etc, that the receiver is capable to
receive. receive.
Optional parameter: cps: This parameter is used to signal the Optional parameter: cps: This parameter is used to signal the
capabilities of a receiver implementation. It indicates the capabilities of a receiver implementation. It indicates the
maximum number of characters that may be received per second maximum number of characters that may be received per second
measured over a period of 10 seconds. The default value is 150. measured over a period of 10 seconds. The default value is 150.
Encoding considerations: binary; see Section 4.8 of [RFC6838]. Encoding considerations: binary; see Section 4.8 of [RFC6838].
Security considerations: See Section 19 of RFC xxxx. [RFC Editor: Security considerations: See Section 20 of RFC xxxx. [RFC Editor:
Upon publication as an RFC, please replace "XXXX" with the number Upon publication as an RFC, please replace "XXXX" with the number
assigned to this document and remove this note.] assigned to this document and remove this note.]
Interoperability considerations: None. Interoperability considerations: None.
Published specification: RFC XXXX. [RFC Editor: Upon publication as Published specification: RFC XXXX. [RFC Editor: Upon publication as
an RFC, please replace "XXXX" with the number assigned to this an RFC, please replace "XXXX" with the number assigned to this
document and remove this note.] document and remove this note.]
Applications which use this media type: For example: Text Applications which use this media type: For example: Text
skipping to change at page 14, line 5 skipping to change at page 14, line 40
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: This media type depends on RTP framing, and Restrictions on usage: This media type depends on RTP framing, and
hence is only defined for transfer via RTP [RFC3550]. hence is only defined for transfer via RTP [RFC3550].
Author: Gunnar Hellstrom <gunnar.hellstrom@ghaccess.se> Author: Gunnar Hellstrom <gunnar.hellstrom@ghaccess.se>
Change controller: IETF AVTCore Working Group delegated from the Change controller: IETF AVTCore Working Group delegated from the
IESG. IESG.
10. SDP considerations 11. SDP considerations
There are receiving RTT implementations which implement RFC 4103 There are receiving RTT implementations which implement RFC 4103
[RFC4103] but not the source separation by the CSRC. Sending mixed [RFC4103] but not the source separation by the CSRC. Sending mixed
text according to the usual CSRC convention from RFC 2198 [RFC2198] text according to the usual CSRC convention from RFC 2198 [RFC2198]
to a device implementing only RFC 4103 [RFC4103] would risk to lead to a device implementing only RFC 4103 [RFC4103] would risk to lead
to unreadable presented text. Therefore, in order to negotiate RTT to unreadable presented text. Therefore, in order to negotiate RTT
mixing capability according to the present specification, all devices mixing capability according to the present specification, all devices
supporting the present specification for multi-party aware supporting the present specification for multi-party aware
participants SHALL include an sdp media format "text/rex" in the sdp, participants SHALL include an sdp media format "text/rex" in the sdp,
indicating this capability in offers and answers. Multi-party indicating this capability in offers and answers. Multi-party
skipping to change at page 14, line 31 skipping to change at page 15, line 18
according to common SDP rules. according to common SDP rules.
The sdp media format defined here, is named "rex", for extended The sdp media format defined here, is named "rex", for extended
redundancy. It is intended to be used in "text" media descriptions redundancy. It is intended to be used in "text" media descriptions
with "text/rex" and "text/t140" formats. Both formats MUST be with "text/rex" and "text/t140" formats. Both formats MUST be
declared for the "text/rex" format to be used. It indicates declared for the "text/rex" format to be used. It indicates
capability to use source indications in the CSRC list and the packet capability to use source indications in the CSRC list and the packet
format according to the present specification. It also indicates format according to the present specification. It also indicates
ability to receive 150 real-time text characters per second. ability to receive 150 real-time text characters per second.
10.1. Security for session control and media 11.1. Security for session control and media
Security SHOULD be applied on both session control and media. In Security SHOULD be applied on both session control and media. In
applications where legacy endpoints without security may exist, a applications where legacy endpoints without security may exist, a
negotiation between security and no security SHOULD be applied. If negotiation between security and no security SHOULD be applied. If
no other security solution is mandated by the application, then RFC no other security solution is mandated by the application, then RFC
8643 OSRTP[RFC8643] SHOULD be applied to negotiate SRTP media 8643 OSRTP[RFC8643] SHOULD be applied to negotiate SRTP media
security with DTLS. Most SDP examples below are expressed without security with DTLS. Most SDP examples below are expressed without
the security additions for simplicity. The principles (but not all the security additions for simplicity. The principles (but not all
details) for applying DTLS-SRTP security is shown in a couple of the details) for applying DTLS-SRTP security is shown in a couple of the
following examples. following examples.
10.2. SDP offer/answer examples 11.2. SDP offer/answer examples
This sections shows some examples of SDP for session negotiation of
the real-time text media in SIP sessions. In the same session
usually audio is provided and sometimes also video. The examples
only show the part of importance for the real-time text media.
Offer example for just multi-party capability: Offer example for just multi-party capability:
m=text 11000 RTP/AVP 101 98 m=text 11000 RTP/AVP 101 98
a=rtpmap:98 t140/1000 a=rtpmap:98 t140/1000
a=rtpmap:101 rex/1000 a=rtpmap:101 rex/1000
a=fmtp:101 98/98/98 a=fmtp:101 98/98/98
Answer example from a multi-party capable device Answer example from a multi-party capable device
m=text 12000 RTP/AVP 101 98 m=text 12000 RTP/AVP 101 98
skipping to change at page 16, line 27 skipping to change at page 17, line 19
A party who has negotiated the "text/rex" capability MUST interpret A party who has negotiated the "text/rex" capability MUST interpret
the contents of the CSRC-list and the packets according to the the contents of the CSRC-list and the packets according to the
present specification in received rtp packets using the corresponding present specification in received rtp packets using the corresponding
payload type. payload type.
A party performing as a mixer, which has not negotiated the "text/ A party performing as a mixer, which has not negotiated the "text/
rex" format, but negotiated a "text/red" or "text/t140" format in a rex" format, but negotiated a "text/red" or "text/t140" format in a
session with a participant SHOULD, if nothing else is specified for session with a participant SHOULD, if nothing else is specified for
the application, format transmitted text to that participant to be the application, format transmitted text to that participant to be
suitable to present on a multi-party unaware endpoint as further suitable to present on a multi-party unaware endpoint as further
specified in section Section 13.2. specified in section Section 14.2.
11. Examples 12. Examples
This example shows a symbolic flow of packets from a mixer with loss This example shows a symbolic flow of packets from a mixer with loss
and recovery. A, B and C are sources of RTT. M is the mixer. Pn and recovery. A, B and C are sources of RTT. M is the mixer. Pn
indicates primary data in source group "n". Rn1 is first redundant indicates primary data in source group "n". Rn1 is first redundant
generation data and Rn2 is second redundant generation data in source generation data and Rn2 is second redundant generation data in source
group "n". A1, B1, A2 etc are text chunks (T140blocks) received from group "n". A1, B1, A2 etc are text chunks (T140blocks) received from
the respective sources. X indicates dropped packet between the mixer the respective sources. X indicates dropped packet between the mixer
and a receiver. and a receiver.
|----------------| |----------------|
skipping to change at page 19, line 5 skipping to change at page 20, line 5
respective reception areas. respective reception areas.
Primary text B3 and A5 are received and appended to their Primary text B3 and A5 are received and appended to their
respective reception areas. respective reception areas.
With only one or two packets lost, there would not be any need to With only one or two packets lost, there would not be any need to
create a missing text marker, and all text would be recovered. create a missing text marker, and all text would be recovered.
It will be a design decision how to present the missing text markers It will be a design decision how to present the missing text markers
assigned to the mixer as a source. assigned to the mixer as a source.
12. Performance considerations 13. Performance considerations
This specification allows new text from 16 sources per packet. This specification allows new text from up to 16 sources per packet.
Packets SHOULD be transmitted with a maximum time interval when there A mixer implementing the specification will normally cause a latency
is text to be transmitted (either primary or redundant) . The default of 0 to 150 milliseconds in text from up to 16 simultaneous sources.
maximum transmission interval is 300 ms. It is also RECOMMENDED for This performance meets well the realistic requirements for conference
the mixer to send a packet as soon as text has been received from a applications for which up to 5 simultaneous sources should not be
source as long as the maximum number of characters per second delayed more than 500 milliseconds by a mixer. In order to achieve
indicated by the recipient is not exceeded, and also the number of good performance, a receiver for multi-party calls SHOULD declare a
packets sent per second to a recipient is kept under a number. In sufficient CPS value in SDP for the number of allowable characters
order to achieve good performance, a receiver for multi-party calls per second.
SHOULD declare a sufficient CPS value in SDP for the number of
allowable characters per second. These characteristics provide for
smooth flow of text with acceptable latency from at least 32 sources
simultaneously.
The default maximum rate of reception of real-time text is in RFC The default maximum rate of reception of real-time text is in RFC
4103 [RFC4103] specified to be 30 characters per second. The value 4103 [RFC4103] specified to be 30 characters per second. The value
MAY be modified in the CPS parameter of the FMTP attribute in the MAY be modified in the CPS parameter of the FMTP attribute in the
media section for RFC 4103. A mixer combining real-time text from a media section for RFC 4103. A mixer combining real-time text from a
number of sources may have a higher combined flow of text coming from number of sources may have a higher combined flow of text coming from
the sources. Endpoints SHOULD therefore specify a suitable higher the sources. Endpoints SHOULD therefore specify a suitable higher
value for the CPS parameter, corresponding to its real reception value for the CPS parameter, corresponding to its real reception
capability. A value for CPS of 150 is the default for the "text/rex" capability. A value for CPS of 150 is the default for the "text/rex"
format. See RFC 4103 [RFC4103] for the format and use of the CPS format. See RFC 4103 [RFC4103] for the format and use of the CPS
parameter. The same rules apply for the "text/rex" format except for parameter. The same rules apply for the "text/rex" format except for
the default value. the default value.
13. Presentation level considerations 14. Presentation level considerations
ITU-T T.140 [T140] provides the presentation level requirements for ITU-T T.140 [T140] provides the presentation level requirements for
the RFC 4103 [RFC4103] transport. T.140 [T140] has functions for the RFC 4103 [RFC4103] transport. T.140 [T140] has functions for
erasure and other formatting functions and has the following general erasure and other formatting functions and has the following general
statement for the presentation: statement for the presentation:
"The display of text from the members of the conversation should be "The display of text from the members of the conversation should be
arranged so that the text from each participant is clearly readable, arranged so that the text from each participant is clearly readable,
and its source and the relative timing of entered text is visualized and its source and the relative timing of entered text is visualized
in the display. Mechanisms for looking back in the contents from the in the display. Mechanisms for looking back in the contents from the
skipping to change at page 20, line 28 skipping to change at page 21, line 21
text to be grouped in presentation. The characters "CRLF" may be text to be grouped in presentation. The characters "CRLF" may be
used by other implementations as replacement for Line Separator. The used by other implementations as replacement for Line Separator. The
"CRLF" combination SHALL be erased by just one erasing action, just "CRLF" combination SHALL be erased by just one erasing action, just
as the Line Separator. Presentation functions are allowed to group as the Line Separator. Presentation functions are allowed to group
text for presentation in smaller groups than the line separators text for presentation in smaller groups than the line separators
imply and present such groups with source indication together with imply and present such groups with source indication together with
text groups from other sources (see the following presentation text groups from other sources (see the following presentation
examples). Erasure has no specific limit by any delimiter in the examples). Erasure has no specific limit by any delimiter in the
text stream. text stream.
13.1. Presentation by multi-party aware endpoints 14.1. Presentation by multi-party aware endpoints
A multi-party aware receiving party, presenting real-time text MUST A multi-party aware receiving party, presenting real-time text MUST
separate text from different sources and present them in separate separate text from different sources and present them in separate
presentation areas. The receiving party MAY separate presentation of presentation fields. The receiving party MAY separate presentation
parts of text from a source in readable groups based on other of parts of text from a source in readable groups based on other
criteria than line separator and merge these groups in the criteria than line separator and merge these groups in the
presentation area when it benefits the user to most easily find and presentation area when it benefits the user to most easily find and
read text from the different participants. The criteria MAY e.g. be read text from the different participants. The criteria MAY e.g. be
a received comma, full stop, or other phrase delimiters, or a long a received comma, full stop, or other phrase delimiters, or a long
pause. pause.
When text is received from multiple original sources, the When text is received from multiple original sources, the
presentation SHOULD provide a view where text is added in multiple presentation SHOULD provide a view where text is added in multiple
places simultaneously. places simultaneously.
skipping to change at page 22, line 17 skipping to change at page 23, line 4
|____________________|______________________|_______________________| |____________________|______________________|_______________________|
| | |I will arrive by TGV. | | | |I will arrive by TGV. |
|My flight is to Orly| |Convenient to the main | |My flight is to Orly| |Convenient to the main |
| |Hi all, can we plan |station. | | |Hi all, can we plan |station. |
| |for the seminar? | | | |for the seminar? | |
|Eve, will you do | | | |Eve, will you do | | |
|your presentation on| | | |your presentation on| | |
|Friday? |Yes, Friday at 10. | | |Friday? |Yes, Friday at 10. | |
|Fine, wo | |We need to meet befo | |Fine, wo | |We need to meet befo |
|___________________________________________________________________| |___________________________________________________________________|
Figure 3: An example of a coordinated column-view of a three-party Figure 3: An example of a coordinated column-view of a three-party
session with entries ordered vertically in approximate time-order. session with entries ordered vertically in approximate time-order.
13.2. Multi-party mixing for multi-party unaware endpoints 14.2. Multi-party mixing for multi-party unaware endpoints
When the mixer has indicated multi-party capability in an sdp When the mixer has indicated multi-party capability in an sdp
negotiation, but the multi-party capability negotiation fails with an negotiation, but the multi-party capability negotiation fails with an
endpoint, then the mixer SHOULD compose a best-effort presentation of endpoint, then the mixer SHOULD compose a best-effort presentation of
multi-party real-time text in one stream intended to be presented by multi-party real-time text in one stream intended to be presented by
an endpoint with no multi-party awareness. an endpoint with no multi-party awareness.
This presentation format has functional limitations and SHOULD be This presentation format has functional limitations and SHOULD be
used only to enable participation in multi-party calls by legacy used only to enable participation in multi-party calls by legacy
deployed endpoints. deployed endpoints.
skipping to change at page 23, line 5 skipping to change at page 23, line 36
simulated limited multi-party RTT view suitable for presentation in simulated limited multi-party RTT view suitable for presentation in
one presentation area. The mixer SHALL group text in suitable groups one presentation area. The mixer SHALL group text in suitable groups
and prepare for presentation of them by inserting a new line betwwen and prepare for presentation of them by inserting a new line betwwen
them if the transmitted text did not already end with a new line. A them if the transmitted text did not already end with a new line. A
presentable label SHOULD be composed and sent for the source presentable label SHOULD be composed and sent for the source
initially in the session and after each source switch. With this initially in the session and after each source switch. With this
procedure the time for source switching is depending on the actions procedure the time for source switching is depending on the actions
of the users. In order to expedite source switch, a user can for of the users. In order to expedite source switch, a user can for
example end its turn with a new line. example end its turn with a new line.
13.2.1. Actions by the mixer at reception from the call participants 14.2.1. Actions by the mixer at reception from the call participants
When text is received by the mixer from the different participants, When text is received by the mixer from the different participants,
the mixer SHALL recover text from redundancy if any packets are lost. the mixer SHALL recover text from redundancy if any packets are lost.
The mark for lost text [T140ad1] SHOULD be inserted in the stream if The mark for lost text [T140ad1] SHOULD be inserted in the stream if
unrecoverable loss appears. Any Unicode BOM characters, possibly unrecoverable loss appears. Any Unicode BOM characters, possibly
used for keep-alive shall be deleted. The time of arrival of text used for keep-alive shall be deleted. The time of arrival of text
SHALL be stored together with the received text from each source in a SHALL be stored together with the received text from each source in a
queue for transmission to the recipients. queue for transmission to the recipients.
13.2.2. Actions by the mixer for transmission to the recipients 14.2.2. Actions by the mixer for transmission to the recipients
The following procedure SHOULD be applied for each recipient of The following procedure SHOULD be applied for each recipient of
multi-part text from the mixer. multi-part text from the mixer.
The text for transmission SHOULD be formatted by the mixer for each The text for transmission SHOULD be formatted by the mixer for each
receiving user for presentation in one single presentation area. receiving user for presentation in one single presentation area.
Text received from a participant SHOULD NOT be included in Text received from a participant SHOULD NOT be included in
transmission to that participant. When there is text available for transmission to that participant. When there is text available for
transmission from the mixer to a receiving party from more than one transmission from the mixer to a receiving party from more than one
participant, the mixer SHOULD switch between transmission of text participant, the mixer SHOULD switch between transmission of text
skipping to change at page 24, line 30 skipping to change at page 25, line 16
Graphic Rendition (SGR) from each source. If there is an SGR code Graphic Rendition (SGR) from each source. If there is an SGR code
stored for the current source before the source switch is done, a stored for the current source before the source switch is done, a
reset of SGR shall be sent by the sequence SGR 0 [009B 0000 006D] reset of SGR shall be sent by the sequence SGR 0 [009B 0000 006D]
after the new line and before the new label during a source switch. after the new line and before the new label during a source switch.
See SGR below for an explanation. This transmission does not See SGR below for an explanation. This transmission does not
influence the display count. If there is an SGR code stored for the influence the display count. If there is an SGR code stored for the
new source after the source switch, that SGR code SHOULD be new source after the source switch, that SGR code SHOULD be
transmitted to the recipient before the label. This transmission transmitted to the recipient before the label. This transmission
does not influence the display count. does not influence the display count.
13.2.3. Actions on transmission of text 14.2.3. Actions on transmission of text
Text from a source sent to the recipient SHOULD increase the display Text from a source sent to the recipient SHOULD increase the display
count by one per transmitted character. count by one per transmitted character.
13.2.4. Actions on transmission of control codes 14.2.4. Actions on transmission of control codes
The following control codes specified by T.140 require specific The following control codes specified by T.140 require specific
actions. They SHOULD cause specific considerations in the mixer. actions. They SHOULD cause specific considerations in the mixer.
Note that the codes presented here are expressed in UCS-16, while Note that the codes presented here are expressed in UCS-16, while
transmission is made in UTF-8 transform of these codes. transmission is made in UTF-8 transform of these codes.
BEL 0007 Bell Alert in session, provides for alerting during an BEL 0007 Bell Alert in session, provides for alerting during an
active session. The display count SHOULD not be altered. active session. The display count SHOULD not be altered.
NEW LINE 2028 Line separator. Check and perform a source switch if NEW LINE 2028 Line separator. Check and perform a source switch if
skipping to change at page 26, line 5 skipping to change at page 26, line 38
to the end of the leading label after a source switch, then the to the end of the leading label after a source switch, then the
mixer must not transmit more backspaces. Instead it is mixer must not transmit more backspaces. Instead it is
RECOMMENDED that a letter "X" is inserted in the text stream for RECOMMENDED that a letter "X" is inserted in the text stream for
each backspace as an indication of the intent to erase more. A each backspace as an indication of the intent to erase more. A
new line is usually coded by a Line Separator, but the character new line is usually coded by a Line Separator, but the character
combination "CRLF" MAY be used instead. Erasure of a new line is combination "CRLF" MAY be used instead. Erasure of a new line is
in both cases done by just one erasing action (Backspace). If the in both cases done by just one erasing action (Backspace). If the
display count has a positive value it is decreased by one when the display count has a positive value it is decreased by one when the
BS is sent. If the display count is at zero, it is not altered. BS is sent. If the display count is at zero, it is not altered.
13.2.5. Packet transmission 14.2.5. Packet transmission
A mixer transmitting to a multi-party unaware terminal SHOULD send A mixer transmitting to a multi-party unaware terminal SHOULD send
primary data only from one source per packet. The SSRC SHOULD be the primary data only from one source per packet. The SSRC SHOULD be the
SSRC of the mixer. The CSRC list SHOULD contain one member and be SSRC of the mixer. The CSRC list SHOULD contain one member and be
the SSRC of the source of the primary data. the SSRC of the source of the primary data.
13.2.6. Functional limitations 14.2.6. Functional limitations
When a multi-party unaware endpoint presents a conversation in one When a multi-party unaware endpoint presents a conversation in one
display area in a chat style, it inserts source indications for display area in a chat style, it inserts source indications for
remote text and local user text as they are merged in completed text remote text and local user text as they are merged in completed text
groups. When an endpoint using this layout receives and presents groups. When an endpoint using this layout receives and presents
text mixed for multi-party unaware endpoints, there will be two text mixed for multi-party unaware endpoints, there will be two
levels of source indicators for the received text; one generated by levels of source indicators for the received text; one generated by
the mixer and inserted in a label after each source switch, and the mixer and inserted in a label after each source switch, and
another generated by the receiving endpoint and inserted after each another generated by the receiving endpoint and inserted after each
switch between local and remote source in the presentation area. switch between local and remote source in the presentation area.
skipping to change at page 26, line 41 skipping to change at page 27, line 34
Erasure can only be done up to the latest source switch. If a user Erasure can only be done up to the latest source switch. If a user
tries to erase more text, the erasing actions will be presented as tries to erase more text, the erasing actions will be presented as
letter X after the label. letter X after the label.
These facts makes it strongly RECOMMENDED to implement multi-party These facts makes it strongly RECOMMENDED to implement multi-party
awareness in RTT endpoints. The use of the mixing method for multi- awareness in RTT endpoints. The use of the mixing method for multi-
party-unaware endpoints should be left for use with endpoints which party-unaware endpoints should be left for use with endpoints which
are impossible to upgrade to become multi-party aware. are impossible to upgrade to become multi-party aware.
13.2.7. Example views of presentation on multi-party unaware endpoints 14.2.7. Example views of presentation on multi-party unaware endpoints
The following pictures are examples of the view on a participant's The following pictures are examples of the view on a participant's
display for the multi-party-unaware case. display for the multi-party-unaware case.
_________________________________________________ _________________________________________________
| Conference | Alice | | Conference | Alice |
|________________________|_________________________| |________________________|_________________________|
| |I will arrive by TGV. | | |I will arrive by TGV. |
|[Bob]:My flight is to |Convenient to the main | |[Bob]:My flight is to |Convenient to the main |
|Orly. |station. | |Orly. |station. |
skipping to change at page 27, line 51 skipping to change at page 28, line 51
|[Eve] But I need to be back to | | |[Eve] But I need to be back to | |
| the hotel by 11 because I need |-| | the hotel by 11 because I need |-|
| |-| | |-|
|______________________________________________|v| |______________________________________________|v|
| of course, I underst | | of course, I underst |
|________________________________________________| |________________________________________________|
Figure 5: An example of a view of the multi-party unaware Figure 5: An example of a view of the multi-party unaware
presentation in chat style. Alice is the local user. presentation in chat style. Alice is the local user.
14. Gateway Considerations 15. Gateway Considerations
14.1. Gateway considerations with Textphones (e.g. TTYs). 15.1. Gateway considerations with Textphones (e.g. TTYs).
Multi-party RTT sessions may involve gateways of different kinds. Multi-party RTT sessions may involve gateways of different kinds.
Gateways involved in setting up sessions SHALL correctly reflect the Gateways involved in setting up sessions SHALL correctly reflect the
multi-party capability or unawareness of the combination of the multi-party capability or unawareness of the combination of the
gateway and the remote endpoint beyond the gateway. gateway and the remote endpoint beyond the gateway.
One case that may occur is a gateway to PSTN for communication with One case that may occur is a gateway to PSTN for communication with
textphones (e.g. TTYs). Textphones are limited devices with no textphones (e.g. TTYs). Textphones are limited devices with no
multi-party awareness, and it SHOULD therefore be suitable for the multi-party awareness, and it SHOULD therefore be suitable for the
gateway to not indicate multi-party awareness for that case. Another gateway to not indicate multi-party awareness for that case. Another
solution is that the gateway indicates multi-party capability towards solution is that the gateway indicates multi-party capability towards
the mixer, and includes the multi-party mixer function for multi- the mixer, and includes the multi-party mixer function for multi-
party unaware endpoints itself. This solution makes it possible to party unaware endpoints itself. This solution makes it possible to
make adaptations for the functional limitations of the textphone make adaptations for the functional limitations of the textphone
(TTY). (TTY).
14.2. Gateway considerations with WebRTC. 15.2. Gateway considerations with WebRTC.
Gateway operation to real-time text in WebRTC may also be required. Gateway operation to real-time text in WebRTC may also be required.
In WebRTC, RTT is specified in draft-ietf-mmusic-t140-usage-data- In WebRTC, RTT is specified in draft-ietf-mmusic-t140-usage-data-
channel[I-D.ietf-mmusic-t140-usage-data-channel]. channel[I-D.ietf-mmusic-t140-usage-data-channel].
A multi-party bridge may have functionality for communicating by RTT A multi-party bridge may have functionality for communicating by RTT
in both RTP streams with RTT and WebRTC t140 data channels. Other in both RTP streams with RTT and WebRTC t140 data channels. Other
configurations may consist of a multi-party bridge with either configurations may consist of a multi-party bridge with either
technology for RTT transport and a separate gateway for conversion of technology for RTT transport and a separate gateway for conversion of
the text communication streams between RTP and t140 data channel. the text communication streams between RTP and t140 data channel.
skipping to change at page 29, line 11 skipping to change at page 30, line 11
rtt, a new t140 channel SHOULD be established to WebRTC users with rtt, a new t140 channel SHOULD be established to WebRTC users with
the label parameter composed from the NAME field in RTCP on the RTP the label parameter composed from the NAME field in RTCP on the RTP
side. side.
When a new participant has entered the multi-party session with RTT When a new participant has entered the multi-party session with RTT
transport in a WebRTC t140 data channel, the new participant SHOULD transport in a WebRTC t140 data channel, the new participant SHOULD
be announced by a notification to RTP users. The label parameter be announced by a notification to RTP users. The label parameter
from the WebRTC side SHOULD be used as the NAME RTCP field on the RTP from the WebRTC side SHOULD be used as the NAME RTCP field on the RTP
side. side.
15. Updates to RFC 4102 and RFC 4103 16. Updates to RFC 4102 and RFC 4103
The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103] by The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103] by
introducing an extended packet format 'text/rex' for the multi-party introducing an extended packet format 'text/rex' for the multi-party
mixing case and more strict rules for the use of redundancy, and mixing case and more strict rules for the use of redundancy, and
population of the CSRC list in the packets. Implications for the population of the CSRC list in the packets. Implications for the
CSRC list use from RFC 2198[RFC2198] are hereby not in effect. CSRC list use from RFC 2198[RFC2198] are hereby not in effect.
16. Congestion considerations 17. Congestion considerations
The congestion considerations and recommended actions from RFC 4103 The congestion considerations and recommended actions from RFC 4103
[RFC4103] are valid also in multi-party situations. [RFC4103] are valid also in multi-party situations.
17. Acknowledgements 18. Acknowledgements
James Hamlin for format input. James Hamlin for format input.
18. IANA Considerations 19. IANA Considerations
The IANA is requested to register the media type registration "text/ The IANA is requested to register the media type registration "text/
rex" as specified in Section 9. The media type is also requested to rex" as specified in Section 10. The media type is also requested to
be added to the IANA registry for "RTP Payload Format Media Types" be added to the IANA registry for "RTP Payload Format Media Types"
<http://www.iana.org/assignments/rtp-parameters>. <http://www.iana.org/assignments/rtp-parameters>.
19. Security Considerations 20. Security Considerations
The RTP-mixer model requires the mixer to be allowed to decrypt, pack The RTP-mixer model requires the mixer to be allowed to decrypt, pack
and encrypt secured text from the conference participants. Therefore and encrypt secured text from the conference participants. Therefore
the mixer needs to be trusted. This is similar to the situation for the mixer needs to be trusted. This is similar to the situation for
central mixers of audio and video. central mixers of audio and video.
The requirement to transfer information about the user in RTCP The requirement to transfer information about the user in RTCP
reports in SDES, CNAME and NAME fields for creation of labels may reports in SDES, CNAME and NAME fields for creation of labels may
have privacy concerns as already stated in RFC 3550 [RFC3550], and have privacy concerns as already stated in RFC 3550 [RFC3550], and
may be restricted of privacy reasons. The receiving user will then may be restricted of privacy reasons. The receiving user will then
get a more symbolic label for the source. get a more symbolic label for the source.
20. Change history 21. Change history
20.1. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-02 21.1. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-03
Mention possible need to mute and raise hands as for other media.
---done ----
Make sure that use in two-party calls is also possible and explained.
- may need more wording -
Clarify the RTT is often used together with other media. --done--
Tell that text mixing is N-1. A users own text is not received in
the mix. -done-
In 3. correct the interval to: A "text/rex" transmitter SHOULD send
packets distributed in time as long as there is something (new or
redundant T140blocks) to transmit. The maximum transmission interval
SHOULD then be 300 ms. It is RECOMMENDED to send a packet to a
receiver as soon as new text to that receiver is available, as long
as the time after the latest sent packet to the same receiver is more
than 150 ms, and also the maximum character rate to the receiver is
not exceeded. The intention is to keep the latency low while keeping
a good protection against text loss in bursty packet loss conditions.
-done-
In 1.3 say that the format is used both ways. -done-
In 13.1 change presentation area to presentation field so that reader
does not think it shall be totally separated. -done-
In Performance and intro, tell the performance in number of
simultaneous sending users and introduced delay 16, 150 vs
requirements 5 vs 500. -done --
Clarify redundancy level per connection. -done-
Timestamp also for the last data header. To make it possible for all
text to have time offset as for transmission from the source. Make
that header equal to the others. -done-
Mixer always use the CSRC list, even for its own BOM. -done-
Combine all talk about transmission interval (300 ms vs when text has
arrived) in section 3 in one paragraph or close to each other. -done-
Documents the goal of good performance with low delay for 5
simultaneous typers in the introduction. -done-
Describe better that only primary text shall be sent on to receivers.
Redundancy and loss must be resolved by the mixer. -done-
21.2. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-02
SDP and better description and visibility of security by OSRTP RFC SDP and better description and visibility of security by OSRTP RFC
8634 needed. 8634 needed.
The description of gatewaying to WebRTC extended. The description of gatewaying to WebRTC extended.
The description of the redundancy header in the packet is improved. The description of the redundancy header in the packet is improved.
20.2. Changes to draft-ietf-avtcore-multi-party-rtt-mix-01 21.3. Changes to draft-ietf-avtcore-multi-party-rtt-mix-01
2,5,6 More efficient format text/rex introduced and attribute a=rtt- 2,5,6 More efficient format text/rex introduced and attribute a=rtt-
mix deleted. mix deleted.
3. Brief about use of OSRTP for security included- More needed. 3. Brief about use of OSRTP for security included- More needed.
4. Brief motivation for the solution and why not rtp-translator is 4. Brief motivation for the solution and why not rtp-translator is
used added to intro. used added to intro.
7. More limitations for the multi-party unaware mixing method 7. More limitations for the multi-party unaware mixing method
inserted. inserted.
8. Updates to RFC 4102 and 4103 more clearly expressed. 8. Updates to RFC 4102 and 4103 more clearly expressed.
9. Gateway to WebRTC started. More needed. 9. Gateway to WebRTC started. More needed.
20.3. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-03 to 21.4. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-03 to
draft-ietf-avtcore-multi-party-rtt-mix-00 draft-ietf-avtcore-multi-party-rtt-mix-00
Changed file name to draft-ietf-avtcore-multi-party-rtt-mix-00 Changed file name to draft-ietf-avtcore-multi-party-rtt-mix-00
Replaced CDATA in IANA registration table with better coding. Replaced CDATA in IANA registration table with better coding.
Converted to xml2rfc version 3. Converted to xml2rfc version 3.
20.4. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-02 to 21.5. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-02 to
-03 -03
Changed company and e-mail of the author. Changed company and e-mail of the author.
Changed title to "RTP-mixer formatting of multi-party Real-time text" Changed title to "RTP-mixer formatting of multi-party Real-time text"
to better match contents. to better match contents.
Check and modification where needed of use of RFC 2119 words SHALL Check and modification where needed of use of RFC 2119 words SHALL
etc. etc.
More about the CC value in sections on transmitters and receivers so More about the CC value in sections on transmitters and receivers so
that 1-to-1 sessions do not use the mixer format. that 1-to-1 sessions do not use the mixer format.
Enhanced section on presentation for multi-party-unaware endpoints Enhanced section on presentation for multi-party-unaware endpoints
A paragraph recommending CPS=150 inserted in the performance section. A paragraph recommending CPS=150 inserted in the performance section.
20.5. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-01 to 21.6. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-01 to
-02 -02
In Abstract and 1. Introduction: Introduced wording about regulatory In Abstract and 1. Introduction: Introduced wording about regulatory
requirements. requirements.
In section 5: The transmission interval is decreased to 100 ms when In section 5: The transmission interval is decreased to 100 ms when
there is text from more than one source to transmit. there is text from more than one source to transmit.
In section 11 about sdp negotiation, a SHOULD-requirement is In section 11 about sdp negotiation, a SHOULD-requirement is
introduced that the mixer should make a mix for multi-party unaware introduced that the mixer should make a mix for multi-party unaware
skipping to change at page 32, line 5 skipping to change at page 34, line 5
In chapter 9. "Use with SIP centralized conferencing framework" the In chapter 9. "Use with SIP centralized conferencing framework" the
following note is inserted: Note: The CSRC-list in an RTP packet only following note is inserted: Note: The CSRC-list in an RTP packet only
includes participants who's text is included in one or more text includes participants who's text is included in one or more text
blocks. It is not the same as the list of participants in a blocks. It is not the same as the list of participants in a
conference. With audio and video media, the CSRC-list would often conference. With audio and video media, the CSRC-list would often
contain all participants who are not muted whereas text participants contain all participants who are not muted whereas text participants
that don't type are completely silent and so don't show up in RTP that don't type are completely silent and so don't show up in RTP
packet CSRC-lists. packet CSRC-lists.
20.6. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-00 to 21.7. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-00 to
-01 -01
Editorial cleanup. Editorial cleanup.
Changed capability indication from fmtp-parameter to sdp attribute Changed capability indication from fmtp-parameter to sdp attribute
"rtt-mix". "rtt-mix".
Swapped order of redundancy elements in the example to match reality. Swapped order of redundancy elements in the example to match reality.
Increased the SDP negotiation section Increased the SDP negotiation section
21. References 22. References
21.1. Normative References 22.1. Normative References
[I-D.ietf-mmusic-t140-usage-data-channel] [I-D.ietf-mmusic-t140-usage-data-channel]
Holmberg, C. and G. Hellstrom, "T.140 Real-time Text Holmberg, C. and G. Hellstrom, "T.140 Real-time Text
Conversation over WebRTC Data Channels", Work in Progress, Conversation over WebRTC Data Channels", Work in Progress,
Internet-Draft, draft-ietf-mmusic-t140-usage-data-channel- Internet-Draft, draft-ietf-mmusic-t140-usage-data-channel-
14, 10 April 2020, <https://tools.ietf.org/html/draft- 14, 10 April 2020, <https://tools.ietf.org/html/draft-
ietf-mmusic-t140-usage-data-channel-14>. ietf-mmusic-t140-usage-data-channel-14>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
skipping to change at page 33, line 5 skipping to change at page 35, line 5
July 2003, <https://www.rfc-editor.org/info/rfc3550>. July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC4102] Jones, P., "Registration of the text/red MIME Sub-Type", [RFC4102] Jones, P., "Registration of the text/red MIME Sub-Type",
RFC 4102, DOI 10.17487/RFC4102, June 2005, RFC 4102, DOI 10.17487/RFC4102, June 2005,
<https://www.rfc-editor.org/info/rfc4102>. <https://www.rfc-editor.org/info/rfc4102>.
[RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text [RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text
Conversation", RFC 4103, DOI 10.17487/RFC4103, June 2005, Conversation", RFC 4103, DOI 10.17487/RFC4103, June 2005,
<https://www.rfc-editor.org/info/rfc4103>. <https://www.rfc-editor.org/info/rfc4103>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://www.rfc-editor.org/info/rfc4566>.
[RFC4855] Casner, S., "Media Type Registration of RTP Payload [RFC4855] Casner, S., "Media Type Registration of RTP Payload
Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007, Formats", RFC 4855, DOI 10.17487/RFC4855, February 2007,
<https://www.rfc-editor.org/info/rfc4855>. <https://www.rfc-editor.org/info/rfc4855>.
[RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for [RFC6263] Marjou, X. and A. Sollaud, "Application Mechanism for
Keeping Alive the NAT Mappings Associated with RTP / RTP Keeping Alive the NAT Mappings Associated with RTP / RTP
Control Protocol (RTCP) Flows", RFC 6263, Control Protocol (RTCP) Flows", RFC 6263,
DOI 10.17487/RFC6263, June 2011, DOI 10.17487/RFC6263, June 2011,
<https://www.rfc-editor.org/info/rfc6263>. <https://www.rfc-editor.org/info/rfc6263>.
skipping to change at page 33, line 35 skipping to change at page 35, line 39
[T140] ITU-T, "Recommendation ITU-T T.140 (02/1998), Protocol for [T140] ITU-T, "Recommendation ITU-T T.140 (02/1998), Protocol for
multimedia application text conversation", February 1998, multimedia application text conversation", February 1998,
<https://www.itu.int/rec/T-REC-T.140-199802-I/en>. <https://www.itu.int/rec/T-REC-T.140-199802-I/en>.
[T140ad1] ITU-T, "Recommendation ITU-T.140 Addendum 1 - (02/2000), [T140ad1] ITU-T, "Recommendation ITU-T.140 Addendum 1 - (02/2000),
Protocol for multimedia application text conversation", Protocol for multimedia application text conversation",
February 2000, February 2000,
<https://www.itu.int/rec/T-REC-T.140-200002-I!Add1/en>. <https://www.itu.int/rec/T-REC-T.140-200002-I!Add1/en>.
21.2. Informative References 22.2. Informative References
[RFC4353] Rosenberg, J., "A Framework for Conferencing with the [RFC4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353, Session Initiation Protocol (SIP)", RFC 4353,
DOI 10.17487/RFC4353, February 2006, DOI 10.17487/RFC4353, February 2006,
<https://www.rfc-editor.org/info/rfc4353>. <https://www.rfc-editor.org/info/rfc4353>.
[RFC4575] Rosenberg, J., Schulzrinne, H., and O. Levin, Ed., "A [RFC4575] Rosenberg, J., Schulzrinne, H., and O. Levin, Ed., "A
Session Initiation Protocol (SIP) Event Package for Session Initiation Protocol (SIP) Event Package for
Conference State", RFC 4575, DOI 10.17487/RFC4575, August Conference State", RFC 4575, DOI 10.17487/RFC4575, August
2006, <https://www.rfc-editor.org/info/rfc4575>. 2006, <https://www.rfc-editor.org/info/rfc4575>.
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