Re: [MMUSIC] draft-holmberg-mmusic-t140-usage-data-channel - language indication

Gunnar Hellström <> Sat, 24 August 2019 09:26 UTC

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Subject: Re: [MMUSIC] draft-holmberg-mmusic-t140-usage-data-channel - language indication
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A bit more about the proposal to add the use of the hlang-send and 
hlang-recv attributes for language negotiation.

Den 2019-08-24 kl. 00:52, skrev Gunnar Hellström:
> 12. At the end of 3.2, add the following about language negotiation
> The users may be interested to negotiate language to use during the 
> real-time text session. This is done by including specifications of 
> language capabilities in the media descriptors for the t140 data 
> channels by use of dsca attributes hlang-send and hlang-recv according 
> to RFC 8373 [RFC8373]. The format is as follows:
> a=dsca:id hlang-send:language
> a=dsca:id hlang-send:language
> The negotiation is performed as indicated in RFC8373.
> -EDITORs NOTE - There may be a need for IANA registration of this way 
> to use the human language attributes. 

RFC 8373 was created partly to satisfy a dependency from 3GPP requiring 
negotiation of language per media. We knew that the T140 text data 
channel was about to be specified, but we could not request IANA to 
register the use of the hlang- attributes because of the state of the 
t140-usage-data channel draft, so the registration request was deleted 
from RFC 8373. It needs to be completed now.

I think the following actions are needed:

12a: Allow use of hlang- attributes together with m=application media 

RFC 8373 has a statement in section 5.3 saying:
"This document does not define the use of language tags in media other 
than interactive streams of audio, video, and text (such as "message" or 
"application"). Such use could be supported by future work or by 
application agreement."

The reason for this limitation is that it must be clear for what 
modality (spoken or written or signed ) the language is intended to be 
used. For audio, text and video, RFC 8373 defines the implicit relation 
audio=spoken, text=written, video=signed, but for "application" there is 
no such implicit relation and it is in our case the subprotocol T140 
that we can be sure carries written language modality. So, we just need 
to specify in the draft that for media "application  / 
webrtc-datachannel" and subprotocol "t140", the language modality is 
"written".  It may in fact be evident from the context.

12b: Allow use of hlang-attributes in dsca parameter values.

RFC 8373 registers SDP parameter att-values hlang-send and hlang-recv 
only for media-level use. The registration requirements in rfc4566bis 
require us to register the use also on dsca(subprotocol) level for the 
t140 subprotocol.

I am not sure how to express that registration. The attributes and 
values are as defined in RFC 8373. We just need to add a usage level for 
SDP att-values hlang-send and hlang-recv for media "application  / 

    o  Usage Level: Add the following
         dcsa(t140)  for written media.

I would appreciate guidance on how this should be expressed in IANA 



Gunnar Hellström
+46 708 204 288