Subject: [AVTCORE] I-D Action: draft-ietf-avtcore-multi-party-rtt-mix-01.txt

From: [email-masked]
Date: Thu, 14 May 2020 07:21:30 -0700

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Audio/Video Transport Core Maintenance WG of the IETF.

        Title           : RTP-mixer formatting of multi-party Real-time text
        Author          : Gunnar Hellstrom
	Filename        : draft-ietf-avtcore-multi-party-rtt-mix-01.txt
	Pages           : 31
	Date            : 2020-05-14

Abstract:
   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
   presented by endpoints in suitable grouping with other text from the
   same source.

   Regional regulatory requirements specify provision of real-time text
   in multi-party calls.  RFC 4103 mixer implementations can use
   traditional RTP functions for source identification, but the mixer
   source switching performance is limited when using the default
   transmission with redundancy.

   An enhancement for RFC 4103 real-time text mixing is provided in the
   present specification, suitable for a centralized conference model
   that enables source identification and efficient source switching.
   The intended use is for real-time text mixers and multi-party-aware
   participant endpoints.  The mechanism builds on use of the CSRC list
   in the RTP packet and an extended packet format 'text/rex'.

   A capability exchange is specified so that it can be verified that a
   participant can handle the multi-party coded real-time text stream.
   The capability is indicated by the media subtype "text/rex".

   The document updates RFC 4102[RFC4102] and RFC 4103[RFC4103]

   A brief description about how a mixer can format text for the case
   when the endpoint is not multi-party aware is also provided.

The IETF datatracker status page for this draft is:
https://datatracker.ietf.org/doc/draft-ietf-avtcore-multi-party-rtt-mix/

There are also htmlized versions available at:
https://tools.ietf.org/html/draft-ietf-avtcore-multi-party-rtt-mix-01
https://datatracker.ietf.org/doc/html/draft-ietf-avtcore-multi-party-rtt-mix-01

A diff from the previous version is available at:
https://www.ietf.org/rfcdiff?url2=draft-ietf-avtcore-multi-party-rtt-mix-01

Please note that it may take a couple of minutes from the time of submission
until the htmlized version and diff are available at tools.ietf.org.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

---

From: Gunnar Hellström <[email-masked]>
Date: Thu, 14 May 2020 16:39:09 +0200

A new version of the multi-party-rtt-mix  draft is available.

This is a brief summary of what has been done, related to the earlier 
announced issues:

New text is started by --

1. Consider rapidly if there is any more reliable transport that is 
feasible to move to.
(e.g. Comedia RFC 4145 and RFC 4572, or the recently approved WebRTC 
t140 data channel draft-ietf-mmusic-t140-data-channel-usage, or use of 
SAVPF with NAK and retransmission RFC 4588)

The answer on issue 1 influences many of the following issues, currently 
written with the assumption that we continue with RTP transport.

---I consider now only two solutions realistic to continue with. That is 
the currently specified RTP-mixer based version and the WebRTC version. 
The draft continues with the RTP-mixer version and includes brief info 
on gatewaying to WebRTC.

2. Add sdp examples

---Done for non-encrypted use. OSRTP use should be added.

3. Add SRTP hints and OSRTP preference (RFC 8643).
--Very briefly mentioned in the SDP section. Need extension.

4. Add a brief motivation for the solution and why not rtp-translator is 
used. (or review rapidly the decision to go with the RTP-mixer model, 
three commenters have wondered why we do not use the rtp-translator model.)
--Done in the introduction.

5 We have indications  that the format with the strict use of the CSRC 
list to indicate sources also of the redundant parts might not be called 
text/red. A new format (e.g. text/rex) may then need to be registered, 
and sdp negotiation made between text/red and text/rex for 
interoperability reasons. Shall we accept that and move on with text/rex 
and the CSRC list that gives switching performance for 5 participants 
within 500 milliseconds delay (as compared to 3 participants within 600 
milliseconds for the text/red format.

--Done. A format "text/rex" specified that can carry text from 16 
participants in each packet.
   The format is as text/red repeated up to 16 times in the packet.
    The earlier proposed attribute a=rtt-mix is not needed anymore and 
is deleted.

6. If we agree to change format to text/rex, then also consider to move 
to the format proposed by James Hamlin, with primary text from up to 16 
participants in each packet. Provides good switching performance 
increase to 16 simultaneous sources.
--Done

7. Describe limitations in the multi-party-unaware case that 
unrecoverable packet loss can hit the label at source switch and 
therefore give the impression that text is coming from another source 
than it is.
--Done. Maybe the main text of the multi-party unaware mixing should 
move to an appendix to be better isolated from the main direction.

8. Make explicit wording about what is to be regarded as update to RFC 
4103. It is important from regulatory points of view in Europe and USA 
that the result can be seen as an update of RFC 4103.
--Done

9. Include brief gateway considerations to WebRTC t140 data channel.
--Briefly done, more needed.

Regards

Gunnar

Den 2020-05-14 kl. 16:21, skrev [email-masked]:
> _______________________________________________
> Audio/Video Transport Core Maintenance
> [email-masked]
> https://www.ietf.org/mailman/listinfo/avt

-- 
Gunnar Hellström
GHAccess
[email-masked]