Subject: [rtcweb] WG last call comments on use-case and requirement document, “Real-time text”

From: Stefan Håkansson LK <[email-masked]>
Date: Mon, 29 Apr 2013 16:02:13 +0200

This relates to the comments to the WG last call of the use-cases and 
requirements document [1].

The topic in this mail is Real-time text. This was discussed in [2] - 
[8] (i hope I found all the relevant mails, please correct me if I 
missed any).

My reading of the discussion is that although there was some interest in 
the use-case it was shown that it can be implemented on top of the 
existing WebRTC environment and thus does not necessary drive any new 
requirements. The counter argument was the need for common
interoperability for real-time text rather than silos, especially in the 
context of emergency services. However as there no consensus on any 
special requirements regarding emergency services it doesn't appear that 
real-time text support requires that either.

This can be summarized to that there was no consensus for additional 
requirements and the basic functionality can clearly be implemented 
using JS and suitable data transport,, and there is no need to add a 
specific use-case for real-time text.

Another way to view this is that the real-time text use-case is a 
"telephony terminal" use-case with the codec being something like T.140, 
which would narrow the discussion to a codec discussion.

Anyway, with the current input I don’t think there is support to add a 
new use-case on “Real-time text”.

Stefan

[1] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06136.html

[2] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06160.html
[3] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06161.html
[4] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06202.html
[5] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06212.html
[6] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06213.html
[7] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06224.html
[8] http://www.ietf.org/mail-archive/web/rtcweb/current/msg06228.html

---

From: Gunnar Hellstrom <[email-masked]>
Date: Tue, 30 Apr 2013 13:09:58 +0200

On 2013-04-29 16:02, Stefan Håkansson LK wrote:
> My reading of the discussion is that although there was some interest 
> in the use-case it was shown that it can be implemented on top of the 
> interoperability for real-time text rather than silos, especially in 
> the context of emergency services. However as there no consensus on 
> any special requirements regarding emergency services it doesn't 
> appear that real-time text support requires that either.
>
> "telephony terminal" use-case with the codec being something like 
> T.140, which would narrow the discussion to a codec discussion.
>
There was interest in having real-time text included in a uniform way in 
rtcweb applications. We took a pause in discussing the topic and agreed 
that a discussion document would be needed describing characteristic and 
pros and cons of three implementation alternatives:
1. RTP implementation alongside with the video and audio media, using 
T.140 on the presentation level and RFC 4103 as RTP packetization.
     This is well defined and easiest to achieve interoperability with 
SIP and emergency services.

2. Rtcweb data channel transport of T.140.
      This requires a standard protocol identity in the data channel so 
that it can be declared and agreed to be used between users of different 
servers. It is more complex to gateway it to SIP and coordinate with the 
other real-time media in a session. The discussion lately about SRTP 
keys have made me unsure if it is really feasible to have real-time text 
using anything else than RTP, because of the need to have all three 
media coordinated in the session.

3. JS implementation in same application as rtcweb usage, but 
transported with another web related mechanism, e.g. XMPP over BOSH.
Possibly using draft XEP-0301 for the real-time text presentation and 
transmission.
A bit complex to do SIP and emergency service interop, but nice as IM 
improvement.
This would also need good work on JS libraries to make it convenient to 
use and opportunities for interop between rtcweb applications high.

It is still my intention to contribute to such document.

On 2013-01-30 I sent a proposal for how to include real-time text in the 
use-case document without indicating the exact solution. I think that 
line should be followed and that it is in line with your discussion of  
"no solution defined".

/Gunnar

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