draft-ietf-avtcore-multi-party-rtt-mix-04.txt   draft-ietf-avtcore-multi-party-rtt-mix-05.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) 1 June 2020 Updates: RFC 4102, RFC 4103 (if approved) 4 June 2020
Intended status: Standards Track Intended status: Standards Track
Expires: 3 December 2020 Expires: 6 December 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-04 draft-ietf-avtcore-multi-party-rtt-mix-05
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
traditional RTP functions for source identification, but the mixer traditional RTP functions for source identification, but the mixer
source switching performance is limited when using the default source switching performance is limited when using the default
transmission with redundancy. transmission with redundancy.
An enhancement for RFC 4103 real-time text mixing is provided in the An enhancement for RFC 4103 real-time text mixing is provided in this
present specification, suitable for a centralized conference model document, suitable for a centralized conference model that enables
that enables source identification and efficient source switching. source identification and efficient source switching. The intended
The intended use is for real-time text mixers and multi-party-aware use is for real-time text mixers and multi-party-aware participant
participant endpoints. The mechanism builds on use of the CSRC list endpoints. The mechanism builds on use of the CSRC list in the RTP
in the RTP packet and an extended packet format 'text/rex'. packet and an extended packet format "text/rex".
A capability exchange is specified so that it can be verified that a A capability exchange is specified so that it can be verified that a
participant can handle the multi-party coded real-time text stream. participant can handle the multi-party coded real-time text stream.
The capability is indicated by the media subtype "text/rex". The capability is indicated by the media subtype "text/rex".
The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103] The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103]
A brief description about how a mixer can format text for the case A brief description about how a mixer can format text for the case
when the endpoint is not multi-party aware is also provided. when the endpoint is not multi-party aware is also provided.
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 3 December 2020. This Internet-Draft will expire on 6 December 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.
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 (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
skipping to change at page 2, line 32 skipping to change at page 2, line 32
extracted from this document must include Simplified BSD License text extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License. provided without warranty as described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Selected solution and considered alternative . . . . . . 5 1.1. Selected solution and considered alternative . . . . . . 5
1.2. Nomenclature . . . . . . . . . . . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . 6
3. Actions at transmission by a mixer . . . . . . . . . . . . . 8 3. Actions at transmission by a mixer . . . . . . . . . . . . . 9
3.1. Initial BOM transmission . . . . . . . . . . . . . . . . 8 3.1. Initial BOM transmission . . . . . . . . . . . . . . . . 9
3.2. Keep-alive . . . . . . . . . . . . . . . . . . . . . . . 9 3.2. Keep-alive . . . . . . . . . . . . . . . . . . . . . . . 9
3.3. Transmission interval . . . . . . . . . . . . . . . . . . 9 3.3. Transmission interval . . . . . . . . . . . . . . . . . . 9
3.4. Do not send to the same source . . . . . . . . . . . . . 9 3.4. Do not send received text to the originating source . . . 9
3.5. Clean incoming text . . . . . . . . . . . . . . . . . . . 9 3.5. Clean incoming text . . . . . . . . . . . . . . . . . . . 10
3.6. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 9 3.6. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 10
3.7. Text placement in packets . . . . . . . . . . . . . . . . 10 3.7. Text placement in packets . . . . . . . . . . . . . . . . 10
3.8. Maximum number of sources per packet . . . . . . . . . . 10 3.8. Maximum number of sources per packet . . . . . . . . . . 10
3.9. Empty T140blocks . . . . . . . . . . . . . . . . . . . . 10 3.9. Empty T140blocks . . . . . . . . . . . . . . . . . . . . 11
3.10. Creation of the redundancy . . . . . . . . . . . . . . . 11 3.10. Creation of the redundancy . . . . . . . . . . . . . . . 11
3.11. Timer offset fields . . . . . . . . . . . . . . . . . . . 11 3.11. Timer offset fields . . . . . . . . . . . . . . . . . . . 11
3.12. Other RTP header fields . . . . . . . . . . . . . . . . . 11 3.12. Other RTP header fields . . . . . . . . . . . . . . . . . 11
3.13. Pause in transmission . . . . . . . . . . . . . . . . . . 11 3.13. Pause in transmission . . . . . . . . . . . . . . . . . . 12
4. Actions at reception . . . . . . . . . . . . . . . . . . . . 12 4. Actions at reception . . . . . . . . . . . . . . . . . . . . 12
4.1. Multi-party vs two-party use . . . . . . . . . . . . . . 12 4.1. Multi-party vs two-party use . . . . . . . . . . . . . . 12
4.2. Level of redundancy . . . . . . . . . . . . . . . . . . . 12 4.2. Level of redundancy . . . . . . . . . . . . . . . . . . . 12
4.3. Extracting text and handling recovery and loss . . . . . 12 4.3. Extracting text and handling recovery and loss . . . . . 12
4.4. Delete BOM . . . . . . . . . . . . . . . . . . . . . . . 13 4.4. Delete BOM . . . . . . . . . . . . . . . . . . . . . . . 13
4.5. Empty T140blocks . . . . . . . . . . . . . . . . . . . . 13 4.5. Empty T140blocks . . . . . . . . . . . . . . . . . . . . 13
5. RTCP considerations . . . . . . . . . . . . . . . . . . . . . 13 5. RTCP considerations . . . . . . . . . . . . . . . . . . . . . 13
6. Chained operation . . . . . . . . . . . . . . . . . . . . . . 13 6. Chained operation . . . . . . . . . . . . . . . . . . . . . . 14
7. Usage without redundancy . . . . . . . . . . . . . . . . . . 13 7. Usage without redundancy . . . . . . . . . . . . . . . . . . 14
8. Use with SIP centralized conferencing framework . . . . . . . 14 8. Use with SIP centralized conferencing framework . . . . . . . 14
9. Conference control . . . . . . . . . . . . . . . . . . . . . 14 9. Conference control . . . . . . . . . . . . . . . . . . . . . 14
10. Media Subtype Registration . . . . . . . . . . . . . . . . . 14 10. Media Subtype Registration . . . . . . . . . . . . . . . . . 14
11. SDP considerations . . . . . . . . . . . . . . . . . . . . . 15 11. SDP considerations . . . . . . . . . . . . . . . . . . . . . 16
11.1. Security for session control and media . . . . . . . . . 16 11.1. Security for session control and media . . . . . . . . . 16
11.2. SDP offer/answer examples . . . . . . . . . . . . . . . 16 11.2. SDP offer/answer examples . . . . . . . . . . . . . . . 16
12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18 12. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18
13. Performance considerations . . . . . . . . . . . . . . . . . 21 13. Performance considerations . . . . . . . . . . . . . . . . . 21
14. Presentation level considerations . . . . . . . . . . . . . . 21 14. Presentation level considerations . . . . . . . . . . . . . . 22
14.1. Presentation by multi-party aware endpoints . . . . . . 22 14.1. Presentation by multi-party aware endpoints . . . . . . 23
14.2. Multi-party mixing for multi-party unaware endpoints . . 24 14.2. Multi-party mixing for multi-party unaware endpoints . . 25
15. Gateway Considerations . . . . . . . . . . . . . . . . . . . 30 15. Gateway Considerations . . . . . . . . . . . . . . . . . . . 30
15.1. Gateway considerations with Textphones (e.g. TTYs). . . 30 15.1. Gateway considerations with Textphones (e.g. TTYs). . . 31
15.2. Gateway considerations with WebRTC. . . . . . . . . . . 31 15.2. Gateway considerations with WebRTC. . . . . . . . . . . 31
16. Updates to RFC 4102 and RFC 4103 . . . . . . . . . . . . . . 31 16. Updates to RFC 4102 and RFC 4103 . . . . . . . . . . . . . . 32
17. Congestion considerations . . . . . . . . . . . . . . . . . . 31 17. Congestion considerations . . . . . . . . . . . . . . . . . . 32
18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
20. Security Considerations . . . . . . . . . . . . . . . . . . . 32 20. Security Considerations . . . . . . . . . . . . . . . . . . . 32
21. Change history . . . . . . . . . . . . . . . . . . . . . . . 32 21. Change history . . . . . . . . . . . . . . . . . . . . . . . 33
21.1. Changes included in 21.1. Changes included in
draft-ietf-avtcore-multi-party-rtt-mix-04 . . . . . . . 32 draft-ietf-avtcore-multi-party-rtt-mix-05 . . . . . . . 33
21.2. Changes included in 21.2. Changes included in
draft-ietf-avtcore-multi-party-rtt-mix-03 . . . . . . . 32 draft-ietf-avtcore-multi-party-rtt-mix-04 . . . . . . . 33
21.3. Changes included in 21.3. Changes included in
draft-ietf-avtcore-multi-party-rtt-mix-02 . . . . . . . 33 draft-ietf-avtcore-multi-party-rtt-mix-03 . . . . . . . 33
21.4. Changes to draft-ietf-avtcore-multi-party-rtt-mix-01 . . 34 21.4. Changes included in
21.5. Changes from draft-ietf-avtcore-multi-party-rtt-mix-02 . . . . . . . 34
21.5. Changes to draft-ietf-avtcore-multi-party-rtt-mix-01 . . 34
21.6. 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 . . . . . . . 34 draft-ietf-avtcore-multi-party-rtt-mix-00 . . . . . . . 34
21.6. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-02 to
-03 . . . . . . . . . . . . . . . . . . . . . . . . . . 34
21.7. Changes from 21.7. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-02 to
-03 . . . . . . . . . . . . . . . . . . . . . . . . . . 35
21.8. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-01 to draft-hellstrom-avtcore-multi-party-rtt-source-01 to
-02 . . . . . . . . . . . . . . . . . . . . . . . . . . 35 -02 . . . . . . . . . . . . . . . . . . . . . . . . . . 35
21.8. Changes from 21.9. Changes from
draft-hellstrom-avtcore-multi-party-rtt-source-00 to draft-hellstrom-avtcore-multi-party-rtt-source-00 to
-01 . . . . . . . . . . . . . . . . . . . . . . . . . . 35 -01 . . . . . . . . . . . . . . . . . . . . . . . . . . 36
22. References . . . . . . . . . . . . . . . . . . . . . . . . . 36 22. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
22.1. Normative References . . . . . . . . . . . . . . . . . . 36 22.1. Normative References . . . . . . . . . . . . . . . . . . 36
22.2. Informative References . . . . . . . . . . . . . . . . . 37 22.2. Informative References . . . . . . . . . . . . . . . . . 38
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 38 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 38
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.
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presentation. Therefore, using RFC 4103 without any extra rule for presentation. Therefore, using RFC 4103 without any extra rule for
source identification, the mixer needs to stop sending new text from source identification, the mixer needs to stop sending new text from
one source and then make sure that all text so far has been sent with one source and then make sure that all text so far has been sent with
all intended redundancy levels (usually two) before switching to all intended redundancy levels (usually two) before switching to
another source. That causes the very long time of one second to another source. That causes the very long time of one second to
switch between transmission of text from one source to text from switch between transmission of text from one source to text from
another source. Both the total throughput and the switching another source. Both the total throughput and the switching
performance in the mixer is too low for most applications. performance in the mixer is too low for most applications.
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. This
present specification introduces a source indicator by specific rules document introduces a source indicator by specific rules for
for populating the CSRC-list and the data header in the RTP-packet. populating the CSRC-list and the data header in the RTP-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 By these extensions, the performance requirements on multi-party
mixing for real-time text are exceeded by the solution in the present mixing for real-time text are exceeded by the solution in this
document. 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
introducing an extended packet format for the multi-party mixing case introducing an extended packet format for the multi-party mixing case
and more strict rules for the use of redundancy. and more strict rules for the source indications.
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 this document makes use of the RTP mixer
mixer model specified in RFC3550[RFC3550]. From some points of view, model specified in RFC3550[RFC3550]. From some points of view, use
use of the RTP translator model specified in RFC 3550 would be more 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 translator model the more common RTP-mixer model was selected. The translator model
would also easier cause congestion if many users send text would also easier cause congestion if many users send text
simultaneously. 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, RTCP, RTP-
in [RFC3550] mixer, RTP-translator are explained 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.
"TTY" stands for a text telephone type used in North America.
"WebRTC" stands for web based communication specified by W3C and
IETF.
"DTLS-SRTP" stnds for security specified in RFC 5764 [RFC5764].
1.3. Intended application 1.3. Intended application
The format for multi-party real-time text is primarily intended for The format for multi-party real-time text is primarily intended for
use in transmission between mixers and endpoints in centralised use in transmission between mixers and endpoints in centralised
mixing configurations. It is also applicable between endpoints as mixing configurations. It is also applicable between endpoints as
well as between 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. This document updates RFC 4102[RFC4102] and RFC
4102[RFC4102] and RFC 4103[RFC4103] by introducing a rule for 4103[RFC4103] by introducing a format "text/rex" with 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 to be called a data header. This is done in the redundancy header to be called a data header. This is done in
order to enhance the performance in multi-party RTT sessions. order to enhance the performance in multi-party RTT sessions.
The "text/rex" format can be seen as an "n-tuple" of the "text/red" The "text/rex" format can be seen as an "n-tuple" of the "text/red"
format intended to carry text information from up to 16 sources per format intended to carry text information from up to 16 sources per
packet. packet.
When transmitted from a mixer, the members in the CSRC-list SHALL The CC field SHALL show the number of members in the CSRC list, which
contain the SSRCs of the sources of the T140blocks in the packet. is one per source represented in the packet.
The order of the CSRC members MUST be the same as the order of
sources of the T140blocks and redundant header fields. When
redundancy is used, text from all included sources MUST have the same
number of redundant generations. The primary, first redundant,
second redundant and possible further redundant generations of
T140blocks MUST be grouped per source in the packet in "source
groups". The recommended level of redundancy is to use one primary
and two redundant generations of T140blocks. In some cases, a
primary or redundant T140block is empty, but is still represented by
a member in the data header.
The CC field SHALL show the number of members in the CSRC list. When transmitted from a mixer, a CSRC list is included in the packet.
The members in the CSRC-list SHALL contain the SSRCs of the sources
of the T140blocks in the packet. The order of the CSRC members MUST
be the same as the order of the sources of the data header fields and
the T140blocks. When redundancy is used, text from all included
sources MUST have the same number of redundant generations. The
primary, first redundant, second redundant and possible further
redundant generations of T140blocks MUST be grouped per source in the
packet in "source groups". The recommended level of redundancy is to
use one primary and two redundant generations of T140blocks. In some
cases, a primary or redundant T140block is empty, but is still
represented by a member in the data header.
The RTP header is followed by one or more source groups of data The RTP header is followed by one or more source groups of data
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 data headers provides the timestamp offset and length of the these data headers provides the timestamp offset and length of the
corresponding data block, in addition to the payload type number corresponding data block, in addition to the payload type number
corresponding to the payload format "text/t140". The data headers corresponding to the payload format "text/t140". The data headers
are followed by the data fields carrying T140blocks from the sources. are followed by the data fields carrying T140blocks from the sources.
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
skipping to change at page 7, line 16 skipping to change at page 7, line 27
resulting time is the time when the data was sent as primary from resulting time is the time when the data was sent as primary from
the original source. If the value would be >15 000, then it SHALL the original source. If the value would be >15 000, then it SHALL
be set to 15 000 plus 300 times the redundancy level of the data. 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 The high values appear only in exceptional cases, e.g. when some
data has been held in order to keep the text flow under the data has been held in order to keep the text flow under the
Characters Per Second (CPS) limit. Characters Per Second (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 the header. block excluding the header.
The last T140block is placed last in the packet. The header for the The header for the final block has a zero F bit, and apart from that
final block has a zero F bit, and apart from that the same fields as the same fields as other data headers.
other data headers.
Note: This specification has a packet format that is similar to that Note: This document has a packet format that is similar to that of
of RFC 2198 [RFC2198] but is different from some aspects. RFC 2198 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 this document a T140block is associated with exactly one CSRC list
one CSRC list member as described above. Also RFC 2198 [RFC2198] member as described above. Also RFC 2198 [RFC2198] anticipates
anticipates infrequent change to CSRCs; implementers should be aware infrequent change to CSRCs; implementers should be aware that the
that the order of the CSRC-list according to this specification will order of the CSRC-list according to this document will vary during
vary during transitions between transmission from the mixer of text transitions between transmission from the mixer of text originated by
originated by different participants. Another difference is that the different participants. Another difference is that the last member
last member in the data header area in RFC 2198 [RFC2198] only in the data header area in RFC 2198 [RFC2198] only contains the
contains the payload type number while in the current specification payload type number while in this document it has the same format as
it has the same format as all other entries in the data header. 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 from three sources and coding according to the party RTT contents from three sources and coding according to this
present specification. document.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| synchronization source (SSRC) identifier | | synchronization source (SSRC) identifier |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
skipping to change at page 8, line 25 skipping to change at page 8, line 40
|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 |timestamp offset of "C-P" |"C-P" block length | |0| T140 PT |timestamp offset of "C-P" |"C-P" block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "A-R2" T.140 encoded redundant data | | "A-R2" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |"A-R1" T.140 encoded redundant data | | |"A-R1" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|"A-P" T.140 encoded primary d. | | |"A-P" T.140 encoded primary | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "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-R1" T.140 encoded redundant data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| "C-P" T.140 encoded primary data | | "C-P" T.140 encoded primary data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2:A 'text/rex' packet with text from three sources A, B, C. Figure 2:A "text/rex" packet with text from three sources A, B, C.
A-P, B-P, C-P are primary data from A, B and C.
A-R1, B-R1, C-R1 are first redundant generation data from A, B and C.
A-R2, B-R2, C-R2 are first redundant generation data from A, B and C.
In a real case, some of the data headers will likely indicate a zero
block length, and no corresponding T.140 data.
3. Actions at transmission by a mixer 3. Actions at transmission by a mixer
3.1. Initial BOM transmission 3.1. Initial BOM transmission
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. If sent to it according to the procedures in this document. If the
the transmitter is a mixer, then the source of this character SHALL transmitter is a mixer, then the source of this character SHALL be
be indicated to be the mixer itself. indicated to be the mixer itself.
3.2. Keep-alive 3.2. Keep-alive
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].
3.3. Transmission interval 3.3. Transmission interval
A "text/rex" transmitter SHOULD send packets distributed in time as A "text/rex" transmitter SHOULD send packets distributed in time as
long as there is something (new or redundant T140blocks) to transmit. long as there is something (new or redundant T140blocks) to transmit.
The maximum transmission interval SHOULD then be 300 ms. It is 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 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 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 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 character rate to the receiver is not exceeded. The intention is to
keep the latency low while keeping a good protection against text keep the latency low while keeping a good protection against text
loss in bursty packet loss conditions. loss in bursty packet loss conditions.
3.4. Do not send to the same source 3.4. Do not send received text to the originating source
Text received from a participant SHOULD NOT be included in Text received from a participant SHOULD NOT be included in
transmission to that participant. transmission to that participant.
3.5. Clean incoming text 3.5. Clean incoming text
A mixer SHALL handle reception and recovery of packet loss, marking A mixer SHALL handle reception and recovery of packet loss, marking
of possible text loss and deletion of 'BOM' characters from each of possible text loss and deletion of 'BOM' characters from each
participant before queueing received text for transmission to participant before queueing received text for transmission to
receiving participants. receiving participants.
skipping to change at page 10, line 19 skipping to change at page 10, line 39
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
SSRC of each source shall be placed as a member in the CSRC-list at a SSRC of each source shall be placed as a member in the CSRC-list at a
place corresponding to the place of its T140blocks in the packet. place corresponding to the place of its T140blocks in the packet.
3.8. Maximum number of sources per packet 3.8. Maximum number of sources per packet
Text from a maximum of 16 sources MAY be included in a packet. The Text from a maximum of 16 sources MAY be included in a packet. The
reason for this limitation is the maximum number of CSRC list reason for this limitation is the maximum number of CSRC list members
members. If text from more sources need to be transmitted, the mixer allowed in a packet. If text from more sources need to be
MAY let the sources take turns in having their text transmitted. transmitted, the mixer MAY let the sources take turns in having their
When stopping transmission of one source to allow another source to text transmitted. When stopping transmission of one source to allow
have its text sent, all intended redundant generations of the last another source to have its text sent, all intended redundant
text from the source to be stopped MUST be transmitted before text generations of the last text from the source to be stopped MUST be
from another source can be transmitted. Actively transmitting transmitted before text from another source can be transmitted.
sources SHOULD be allowed to take turns with short intervals to have Actively transmitting sources SHOULD be allowed to take turns with
their text transmitted. short intervals to have their text transmitted.
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 text blocks. It is not the same as the total text is included in text blocks. It is not the same as the total
list of participants in a conference. With audio and video media, list of participants in a conference. With audio and video media,
the CSRC-list would often contain all participants who are not muted the CSRC-list would often contain all participants who are not muted
whereas text participants that don't type are completely silent and whereas text participants that don't type are completely silent and
thus are not represented in RTP packet CSRC-lists once their text thus are not represented in RTP packet CSRC-lists once their text
have been transmitted as primary and the intended number of redundant have been transmitted as primary and the intended number of redundant
generations. generations.
3.9. Empty T140blocks 3.9. Empty T140blocks
If no unsent T140blocks were available at this time for a source, but If no unsent T140blocks were available for a source at the time of
T140blocks are available which have not yet been sent the full populating a packet, but T140blocks are available which have not yet
intended number of redundant transmissions, then the primary been sent the full intended number of redundant transmissions, then
T140block for that source is composed of an empty T140block, and the primary T140block for that source is composed of an empty
populated (without taking up any length) in a packet for T140block, and populated (without taking up any length) in a packet
transmission. The corresponding SSRC SHALL be placed in its place in for transmission. The corresponding SSRC SHALL be placed in its
the CSRC-list. place in the CSRC-list.
3.10. Creation of the redundancy 3.10. Creation of the redundancy
The primary T140block from each source in the latest transmission is The primary T140block from each source in the latest transmitted
used to populate the first redundant T140block for that source. The packet is used to populate the first redundant T140block for that
first redundant T140block for that source from the latest source. The first redundant T140block for that source from the
transmission is placed as the second redundant T140block source. latest transmission is placed as the second redundant T140block
source.
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
used by the transmitter. maximum used by the transmitter.
3.11. Timer offset fields 3.11. Timer offset fields
The timer offset values are inserted in the data header, with the The timer offset values are inserted in the data header, with the
time offset from the RTP timestamp in the packet when the time offset from the RTP timestamp in the packet when the
corresponding T140block was sent from its original source as primary. corresponding T140block was sent from its original source as primary.
The timer offsets are expressed in the same clock tick units as the
RTP timestamp.
The timestamp offset values for empty T140blocks have no relevance The timestamp offset values for empty T140blocks have no relevance
but SHOULD be assigned realistic values. but SHOULD be assigned realistic values.
3.12. Other RTP header fields 3.12. Other RTP header fields
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.
The current time SHALL be inserted in the timestamp. The current time SHALL be inserted in the timestamp.
skipping to change at page 13, line 48 skipping to change at page 14, line 15
6. Chained operation 6. Chained operation
By strictly applying the rules for "text/rex" packet format by all By strictly applying the rules for "text/rex" packet format by all
conforming devices, mixers MAY be arranged in chains. conforming devices, mixers MAY be arranged in chains.
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 this document SHALL be
be applied except the redundant generations in transmission. 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 suitable 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
skipping to change at page 15, line 45 skipping to change at page 16, line 12
Change controller: IETF AVTCore Working Group delegated from the Change controller: IETF AVTCore Working Group delegated from the
IESG. IESG.
11. 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 this document, all devices supporting
supporting the present specification for multi-party aware this document for multi-party aware participants SHALL include an SDP
participants SHALL include an SDP media format "text/rex" in the SDP media format "text/rex" in the SDP [RFC4566], indicating this
[RFC4566], indicating this capability in offers and answers. Multi- capability in offers and answers. Multi-party streams using the
party streams using the coding of the present specification intended coding of this document intended for multi-party aware endpoints MUST
for multi-party aware endpoints MUST NOT be sent to devices which NOT be sent to devices which have not indicated the "text/rex"
have not indicated the "text/rex" format. format.
Implementations not understanding this format MUST ignore it Implementations not understanding this format MUST ignore it
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
"red". It is intended to be used in "text" media descriptions with "red". It is intended to be used in "text" media descriptions with
"text/rex" and "text/t140" formats. Both formats MUST be declared "text/rex" and "text/t140" formats. Both formats MUST be declared
for the "text/rex" format to be used. It indicates capability to use for the "text/rex" format to be used. It indicates capability to use
source indications in the CSRC list and the packet format according source indications in the CSRC list and the packet format according
to the present specification. It also indicates ability to receive to this document. It also indicates ability to receive 150 real-time
150 real-time text characters per second by default. text characters per second by default.
11.1. 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 for simplicity
the security additions for simplicity. The principles (but not all expressed without the security additions. The principles (but not
details) for applying DTLS-SRTP security is shown in a couple of the all details) for applying DTLS-SRTP security is shown in a couple of
following examples. the following examples.
11.2. SDP offer/answer examples 11.2. SDP offer/answer examples
This sections shows some examples of SDP for session negotiation of This sections shows some examples of SDP for session negotiation of
the real-time text media in SIP sessions. Audio is usually provided the real-time text media in SIP sessions. Audio is usually provided
in the same session, and sometimes also video. The examples only in the same session, and sometimes also video. The examples only
show the part of importance for the real-time text media. 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:
skipping to change at page 18, line 6 skipping to change at page 18, line 24
Answer example from a multi-party unaware device that also Answer example from a multi-party unaware device that also
does not support security: does not support security:
m=text 12000 RTP/AVP 100 98 m=text 12000 RTP/AVP 100 98
a=rtpmap:98 t140/1000 a=rtpmap:98 t140/1000
a=rtpmap:100 red/1000 a=rtpmap:100 red/1000
a=fmtp:100 98/98/98 a=fmtp:100 98/98/98
A party which has negotiated the "text/rex" format MUST populate the A party which has negotiated the "text/rex" format MUST populate the
CSRC-list and format the packets according to the present CSRC-list and format the packets according to this document if it
specification if it acts as an rtp-mixer and sends multi-party text. acts as an rtp-mixer and sends multi-party text.
A party which has negotiated the "text/rex" capability MUST interpret A party which 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 this
present specification in received rtp packets using the corresponding document in received rtp packets using the corresponding payload
payload type. 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 14.2. specified in section Section 14.2.
A party not performing as a mixer MUST not include the CSRC list if A party not performing as a mixer MUST not include the CSRC list if
it has a single source of text. it has a single source of text.
skipping to change at page 21, line 10 skipping to change at page 21, line 26
mark in time between A1 and A3. mark in time between A1 and A3.
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.
13. Performance considerations 13. Performance considerations
This specification allows new text from up to 16 sources per packet. This document allows new text from up to 16 sources per packet. A
A mixer implementing the specification will normally cause a latency mixer implementing the specification will normally cause a latency of
of 0 to 150 milliseconds in text from up to 16 simultaneous sources. 0 to 150 milliseconds in text from up to 16 simultaneous sources.
This performance meets well the realistic requirements for conference This performance meets well the realistic requirements for conference
and conversational applications for which up to 5 simultaneous and conversational applications for which up to 5 simultaneous
sources should not be delayed more than 500 milliseconds by a mixer. sources should not be delayed more than 500 milliseconds by a mixer.
In order to achieve good performance, a receiver for multi-party In order to achieve good performance, a receiver for multi-party
calls SHOULD declare a sufficient CPS value in SDP for the number of calls SHOULD declare a sufficient CPS value in SDP for the number of
allowable characters per second. allowable characters per second.
As comparison, if the "text/red" format would be used for multi-party As comparison, if the "text/red" format would be used for multi-party
communication with its default timing and redundancy, 5 communication with its default timing and redundancy, 5
simultaneously sending parties would cause jerky presentation of the simultaneously sending parties would cause jerky presentation of the
skipping to change at page 22, line 12 skipping to change at page 22, line 29
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
current session should be provided. The text should be displayed as current session should be provided. The text should be displayed as
soon as it is received." soon as it is received."
Strict application of T.140 [T140] is of essence for the Strict application of T.140 [T140] is of essence for the
interoperability of real-time text implementations and to fulfill the interoperability of real-time text implementations and to fulfill the
intention that the session participants have the same information of intention that the session participants have the same information of
the text contents of the conversation without necessarily having the the text contents of the conversation without necessarily having the
exact same layout of the conversation. This also includes the exact same layout of the conversation.
ability to ignore optional presentation control codes not supported
by a receiving application.
T.140 [T140] specifies a set of presentation control codes to include T.140 [T140] specifies a set of presentation control codes to include
in the stream. Some of them are optional. Implementations MUST be in the stream. Some of them are optional. Implementations MUST be
able to ignore optional control codes that they do not support. able to ignore optional control codes that they do not support.
There is no strict "message" concept in real-time text. Line There is no strict "message" concept in real-time text. Line
Separator SHALL be used as a separator allowing a part of received Separator SHALL be used as a separator allowing a part of received
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
skipping to change at page 23, line 17 skipping to change at page 24, line 7
local user ended at suitable points merged with received text to local user ended at suitable points merged with received text to
indicate the relative timing for when the text groups were completed. indicate the relative timing for when the text groups were completed.
In this presentation mode, the receiving endpoint SHALL present the In this presentation mode, the receiving endpoint SHALL present the
source of the different groups of text. source of the different groups of text.
A view of a three-party RTT call in chat style is shown in this A view of a three-party RTT call in chat style is shown in this
example . example .
_________________________________________________ _________________________________________________
| |^| | |^|
|[Alice] Hi, Alice here. | | |[Alice] Hi, Alice here. |-|
| | | | | |
|[Bob] Bob as well. | | |[Bob] Bob as well. | |
| | | | | |
|[Eve] Hi, this is Eve, calling from Paris. | | |[Eve] Hi, this is Eve, calling from Paris. | |
| I thought you should be here. | | | I thought you should be here. | |
| | | | | |
|[Alice] I am coming on Thursday, my | | |[Alice] I am coming on Thursday, my | |
| performance is not until Friday morning.| | | performance is not until Friday morning.| |
| | | | | |
|[Bob] And I on Wednesday evening. | | |[Bob] And I on Wednesday evening. | |
| | | | | |
|[Alice] Can we meet on Thursday evening? | | |[Alice] Can we meet on Thursday evening? | |
| | | | | |
|[Eve] Yes, definitely. How about 7pm. | | |[Eve] Yes, definitely. How about 7pm. | |
| at the entrance of the restaurant | | | at the entrance of the restaurant | |
| Le Lion Blanc? | | | Le Lion Blanc? | |
|[Eve] we can have dinner and then take a walk |-| |[Eve] we can have dinner and then take a walk |-|
|______________________________________________|V| |______________________________________________|v|
| <Eve-typing> But I need to be back to |^| | <Eve-typing> But I need to be back to |^|
| the hotel by 11 because I need |-| | the hotel by 11 because I need |-|
| |-| | | |
| <Bob-typing> I wou |-| | <Bob-typing> I wou |-|
|______________________________________________|v| |______________________________________________|v|
| of course, I underst | | of course, I underst |
|________________________________________________| |________________________________________________|
Figure 3: Example of a three-party RTT call presented in chat style Figure 3: Example of a three-party RTT call presented in chat style
seen at participant 'Alice's endpoint. seen at participant 'Alice's endpoint.
Other presentation styles than the chat style may be arranged. Other presentation styles than the chat style may be arranged.
skipping to change at page 24, line 17 skipping to change at page 25, 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 4: An example of a coordinated column-view of a three-party Figure 4: 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.
14.2. 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 by the "text/rex"
negotiation, but the multi-party capability negotiation fails with an format in an SDP negotiation, but the multi-party capability
endpoint, then the mixer SHOULD compose a best-effort presentation of negotiation fails with an endpoint, then the agreed "text/red" or
multi-party real-time text in one stream intended to be presented by "text/t140" format SHALL be used and the mixer SHOULD compose a best-
an endpoint with no multi-party awareness. effort presentation of multi-party real-time text in one stream
intended to be presented by 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 implementing only RFC 4103 without the multi-party deployed endpoints implementing only RFC 4103 without the multi-party
extension specified in the current document. extension specified in this document.
The principles and procedures below do not specify any new protocol The principles and procedures below do not specify any new protocol
elements or behaviors. They are instead composed from the elements. They are instead composed from the information in ITU-T
information in ITU-T T.140 [T140] and an ambition to provide a best T.140 [T140] and an ambition to provide a best effort presentation on
effort presentation on an endpoint which has functions only for two- an endpoint which has functions only for two-party calls.
party calls.
The mixer mixing for multi-party unaware endpoints SHALL compose a The mixer mixing for multi-party unaware endpoints SHALL compose a
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 between and prepare for presentation of them by inserting a new line between
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.
14.2.1. 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 creation of text used for keep-alive shall be deleted. The time of creation of text
(retrieved from the RTP timestamp) SHALL be stored together with the (retrieved from the RTP timestamp) SHALL be stored together with the
received text from each source in queues for transmission to the received text from each source in queues for transmission to the
recipients. recipients.
14.2.2. 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.
skipping to change at page 27, line 22 skipping to change at page 28, line 13
SOS 0098 Start of string, used as a general protocol element SOS 0098 Start of string, used as a general protocol element
introducer, followed by a maximum 256 bytes string and the ST. introducer, followed by a maximum 256 bytes string and the ST.
The display count SHOULD not be altered. The display count SHOULD not be altered.
ST 009C String terminator, end of SOS string. The display count ST 009C String terminator, end of SOS string. The display count
SHOULD not be altered. SHOULD not be altered.
ESC 001B Escape - used in control strings. The display count SHOULD ESC 001B Escape - used in control strings. The display count SHOULD
not be altered for the complete escape code. not be altered for the complete escape code.
Byte order mark 'BOM* FEFF Zero width, no break space, used for Byte order mark "BOM" (U+FEFF) "Zero width, no break space", used
synchronization and keep-alive. SHOULD be deleted from incoming for synchronization and keep-alive. SHOULD be deleted from
streams. Shall be sent first after session establishment to the incoming streams. Shall be sent first after session establishment
recipient. The display count shall not be altered. to the recipient. The display count shall not be altered.
Missing text mark FFFD Replacement character, represented as a Missing text mark (U+FFFD) "Replacement character", represented as a
question mark in a rhombus, or if that is not feasible, replaced question mark in a rhombus, or if that is not feasible, replaced
by an apostrophe ', marks place in stream of possible text loss. by an apostrophe ', marks place in stream of possible text loss.
SHOULD be inserted by the reception procedure in case of SHOULD be inserted by the reception procedure in case of
unrecoverable loss of packets. The display count SHOULD be unrecoverable loss of packets. The display count SHOULD be
increased by one when sent as for any other character. increased by one when sent as for any other character.
SGR If a control code for selecting graphic rendition (SGR), other SGR If a control code for selecting graphic rendition (SGR), other
than reset of the graphic rendition (SGR 0) is sent to a than reset of the graphic rendition (SGR 0) is sent to a
recipient, that control code shall also be stored as status for recipient, that control code shall also be stored as status for
the source in the storage for SGR status. If a reset graphic the source in the storage for SGR status. If a reset graphic
rendition (SGR 0) originated from a source is sent, then the SGR rendition (SGR 0) originated from a source is sent, then the SGR
status storage for that source shall be cleared. The display status storage for that source shall be cleared. The display
count shall not be increased. count shall not be increased.
BS 0008 Back Space, intended to erase the last entered character by BS (U+0008) Back Space, intended to erase the last entered character
a source. Erasure by backspace cannot always be performed as the by a source. Erasure by backspace cannot always be performed as
erasing party intended. If an erasing action erases all text up the erasing party intended. If an erasing action erases all text
to the end of the leading label after a source switch, then the up 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.
14.2.5. Packet transmission 14.2.5. Packet transmission
skipping to change at page 30, line 7 skipping to change at page 30, line 27
|[Eve]:Yes, Friday at 10.| | |[Eve]:Yes, Friday at 10.| |
|[Bob]: Fine, wo |We need to meet befo | |[Bob]: Fine, wo |We need to meet befo |
|________________________|_________________________| |________________________|_________________________|
Figure 5: Alice who has a conference-unaware client is receiving the Figure 5: Alice who has a conference-unaware client is receiving the
multi-party real-time text in a single-stream. This figure shows how multi-party real-time text in a single-stream. This figure shows how
a coordinated column view MAY be presented on Alice's device. a coordinated column view MAY be presented on Alice's device.
_________________________________________________ _________________________________________________
| |^| | |^|
|[Alice] Hi, Alice here. | | |[Alice] Hi, Alice here. |-|
| | | | | |
|[mix][Bob] Bob as well. | | |[mix][Bob] Bob as well. | |
| | | | | |
|[Eve] Hi, this is Eve, calling from Paris | | |[Eve] Hi, this is Eve, calling from Paris | |
| I thought you should be here. | | | I thought you should be here. | |
| | | | | |
|[Alice] I am coming on Thursday, my | | |[Alice] I am coming on Thursday, my | |
| performance is not until Friday morning.| | | performance is not until Friday morning.| |
| | | | | |
|[mix][Bob] And I on Wednesday evening. | | |[mix][Bob] And I on Wednesday evening. | |
| | | | | |
|[Eve] we can have dinner and then walk | | |[Eve] we can have dinner and then walk | |
| | | | | |
|[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 6: An example of a view of the multi-party unaware Figure 6: 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.
15. Gateway Considerations 15. Gateway Considerations
15.1. 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
skipping to change at page 31, line 42 skipping to change at page 32, line 14
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, or other available session information. side, or other available session information.
16. Updates to RFC 4102 and RFC 4103 16. Updates to RFC 4102 and RFC 4103
This document updates RFC 4102[RFC4102] and RFC 4103[RFC4103] by This 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.
17. 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.
The first action in case of congestion SHOULD be to temporarily
increase the transmission interval up to one second.
18. Acknowledgements 18. Acknowledgements
James Hamlin for format input. James Hamlin for format input.
19. 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 "text/rex" as
rex" as specified in Section 10. The media type is also requested to specified in Section 10. The media type is also requested to be
be added to the IANA registry for "RTP Payload Format Media Types" 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>.
20. 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, and in conference
have privacy concerns as already stated in RFC 3550 [RFC3550], and notifications, for creation of labels may have privacy concerns as
may be restricted of privacy reasons. The receiving user will then already stated in RFC 3550 [RFC3550], and may be restricted of
get a more symbolic label for the source. privacy reasons. The receiving user will then get a more symbolic
label for the source.
21. Change history 21. Change history
21.1. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-04 21.1. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-05
nomenclature and editorial improvements
"this document" used consistently to refer to this document.
21.2. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-04
'Redundancy header' renamed to 'data header'. 'Redundancy header' renamed to 'data header'.
More clarifications added. More clarifications added.
Language and figure number corrections. Language and figure number corrections.
21.2. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-03 21.3. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-03
Mention possible need to mute and raise hands as for other media. Mention possible need to mute and raise hands as for other media.
---done ---- ---done ----
Make sure that use in two-party calls is also possible and explained. Make sure that use in two-party calls is also possible and explained.
- may need more wording - - may need more wording -
Clarify the RTT is often used together with other media. --done-- 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 Tell that text mixing is N-1. A users own text is not received in
skipping to change at page 33, line 41 skipping to change at page 34, line 21
Combine all talk about transmission interval (300 ms vs when text has 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- arrived) in section 3 in one paragraph or close to each other. -done-
Documents the goal of good performance with low delay for 5 Documents the goal of good performance with low delay for 5
simultaneous typers in the introduction. -done- simultaneous typers in the introduction. -done-
Describe better that only primary text shall be sent on to receivers. Describe better that only primary text shall be sent on to receivers.
Redundancy and loss must be resolved by the mixer. -done- Redundancy and loss must be resolved by the mixer. -done-
21.3. Changes included in draft-ietf-avtcore-multi-party-rtt-mix-02 21.4. 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 data header in the packet is improved. The description of the data header in the packet is improved.
21.4. Changes to draft-ietf-avtcore-multi-party-rtt-mix-01 21.5. 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
mix deleted. a=rtt-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.
21.5. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-03 to 21.6. 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.
21.6. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-02 to 21.7. 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.
21.7. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-01 to 21.8. 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 35, line 45 skipping to change at page 36, line 21
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.
21.8. Changes from draft-hellstrom-avtcore-multi-party-rtt-source-00 to 21.9. 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
skipping to change at page 37, line 5 skipping to change at page 37, line 32
<https://www.rfc-editor.org/info/rfc4103>. <https://www.rfc-editor.org/info/rfc4103>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566, Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://www.rfc-editor.org/info/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>.
[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
Security (DTLS) Extension to Establish Keys for the Secure
Real-time Transport Protocol (SRTP)", RFC 5764,
DOI 10.17487/RFC5764, May 2010,
<https://www.rfc-editor.org/info/rfc5764>.
[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>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
 End of changes. 83 change blocks. 
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