Re: [MMUSIC] draft-holmberg-mmusic-t140-usage-data-channel-gateway considerations

Paul Kyzivat <> Thu, 29 August 2019 15:21 UTC

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Date: Thu, 29 Aug 2019 11:20:56 -0400
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Subject: Re: [MMUSIC] draft-holmberg-mmusic-t140-usage-data-channel-gateway considerations
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On 8/29/19 5:07 AM, Gunnar Hellström wrote:
> Hi Christer,
> Den 2019-08-29 kl. 10:37, skrev Christer Holmberg:

>> The data channel itself is always bi-directional. Now, if you want to 
>> allow usage of direction attributes for T.140 data I guess we would 
>> have to define usage of them inside a 'dcsa' attribute.
> If it is common to use these attributes for muting etc in conferencing 
> scenarios for other media, I think they should be mentioned and 
> registered. The action on the T.140 data channel needs then be on 
> application level. That provides an opportunity to indicate in the user 
> interface that what the user types is not transmitted in case of muted. 
> If other mechanisms are usually used for other media, we could ignore 
> these attributes.

I think it may make sense to use sendonly/recvonly here. Doing so will 
require *some* document to specify that and update the registration of 
those attributes to indicate it.

But I don't think it is sufficient to simply add IANA considerations to 
update the registry. The use of sendrecv/sendonly/recvonly/inactive, as 
specified in rfc4566bis, is strongly linked (at least implicitly) to how 
RTP works. To use them in this new context I think there needs to be a 
document that discusses the details.