Re: [MMUSIC] WGLC for draft-ietf-mmusic-data-channel-sdpneg

[Flemming Andreasen <[e-mail]>]

Hi Juergen

Thanks for putting together the summary. Option B(ii) below would indeed 
be my preference.

-- Flemming (as individual)

On 3/8/16 8:51 AM, Juergen Stoetzer-Bradler wrote:
> Flemming, Paul, Christian,
>
> Trying to summarize, as per my understanding following three main 
> options (A), (B) and (C) have been discussed in this email thread 
> regarding the IANA registration of SDP attributes.
>
> (A) "One new global IANA registry for data channel subprotocol 
> attributes, common for all data channel subprotocols":
> Similar to IANA's RTP source level attribute registry a global IANA 
> "data channel level" attribute registry could be created.
>     (i) Either, this registry could list all existing (and potential 
> future) attributes, and for each attribute could state if it could 
> also be used as dcsa embedded attribute associated with certain data 
> channel subprotocols. Each attribute within this registry might then 
> be associated with zero, one or multiple document references, where 
> each referenced document should describe this attribute's semantic and 
> usage for a specific subprotocol. (Which would not exclude one 
> document describing an attribute's semantic and usage for more than 
> just one data channel subprotocol.)
>     (ii) Or, this registry could list only those existing (and 
> potential future) attributes, which have already been identified as 
> data channel subprotocol attributes. All such already identified data 
> channel subprotocol attributes could be listed in that registry, 
> regardless of whether or not the usage of these attributes is specific 
> for data channel transport. Each attributes listed in this registry 
> could be associated with one or multiple document references. Each 
> such a reference could point to a document which could either describe 
> the data channel transport specific usage of this attribute for one or 
> several data channel subprotocols. Or such a reference could point to 
> the document, which defines this attribute in a data channel 
> independent / generic way (if usage of this attribute does not have 
> data channel transport specific aspects).
>     (iii) Or, this registry could only list those existing (and 
> potential future) attributes, which have already been identified as 
> data channel subprotocol attributes, and whose usage is indeed data 
> channel transport specific. Similar as in (ii) each attribute listed 
> in this registry could be associated with one or multiple document 
> references. Each such reference could point to a document which could 
> describe the data channel transport specific usage of this attribute 
> for one or several data channel subprotocols.
>
> (B) "For each data channel subprotocol one new dedicated attribute 
> registry":
> The document, which requests to add the data channel subprotocol's 
> identifier to the IANA WebSocket subprotocol name registry, could 
> additionally request to create a new IANA registry, specific for this 
> subprotocol, which could list all attributes, which can be used as 
> a=dcsa embedded attributes for this data channel subprotocol. Similar 
> as in (A) there seem to be (at least) two sub-options:
>     (i) Either, this subprotocol specific registry could list all 
> attributes, which could be used for this subprotocol (and have already 
> been identified as such) in case of data channel transport. Each such 
> attribute could then be associated with exactly one document 
> reference, where this reference either could point to a document, 
> which describes the data channel transport specific usage of this 
> attribute for this specific subprotocol, or could point to a document, 
> which specifies this attribute in a data channel independent way.
>     (ii) Or, this subprotocol specific registry could only list those 
> attributes, which could be used for this subprotocol, and which have a 
> data channel transport specific semantic. Each such attribute could 
> then be associated with a document describing this data channel 
> transport specific semantic for this subprotocol.
>
> (C) "No data channel specific registry(s) - re-use of the already 
> existing session and media level or media level only registries":
> The document, which requests to add the data channel subprotocol's 
> identifier to the IANA Websocket subprotocol id registry, could 
> additionally describe the usages of those attributes, which may be 
> used for this data channel subprotocol, and whose usages and/or 
> semantics have data channel transport specific aspects. However, if 
> those attributes did already exist prior to the creation of this data 
> channel subprotocol document, then the already existing IANA 
> registrations of those attributes would not be modified. If this data 
> channel subprotocol describing document introduced new subprotocol 
> specific attributes, then it could request these to be added to the 
> exiting media level only attribute registry. Subsequently, if a later 
> document introduces new attributes, which could also be used for that 
> subprotocol in the data channel transport case, then that later 
> document could describe this data channel subprotocol specific usage, 
> and could also add these attributes to the existing session and media 
> level or media level only attribute registry.
>
>
> If I am not mistaken then (A)(i) was the option which Paul initially 
> mentioned in this email thread. And Paul also mentioned a variant, 
> where the already existing attribute registries could be merged into 
> just one, where a new field could be added describing the attribute's 
> scope (which then could contain more than just one scope), and where 
> also 'data channel level' could be an attribute's scope. In such a 
> case different scopes might potentially refer to different documents.
> In his last email Christian did also refer to option (A), I think.
> Option (B) was mentioned by Flemming, where he expressed a preference 
> for (B)(i), as far as I understood.
> Option (C) is the one which is (to the most part) described in current 
> version 08 of draft-ietf-mmusic-data-channel-sdpneg.
>
> Would there be another option, which I haven't described above?
>
> Would there be one (sub-)option, everybody could live with?
>
> Based on this discussion, if option (C) isn't agreeable, then I myself 
> would prefer option (B), with a tendency to (B)(ii), as this might 
> provide more flexibility for implementations, which want to use an 
> attribute for a data channel subprotocol with its original (data 
> channel transport independent) semantic, also if this attribute has 
> not been added to the data channel subprotocol specific attribute 
> registry. And as I still think that most of those attributes would be 
> used transport protocol stack independently.
>
> Thanks again,
> Juergen
>
>
>
> On 08.03.2016 04:04, EXT Flemming Andreasen wrote:
>>
>>
>> On 3/6/16 7:04 PM, Christian Groves wrote:
>>> Hello Flemming and Juergen,
>>>
>>> ..snip..
>>>>> I agree that in such cases such new attributes could indeed be 
>>>>> added to corresponding data channel subprotocol specific attribute 
>>>>> registries, which then could refer to the document introducing 
>>>>> this new attribute.
>>>> Right - and for consistency I think it then makes sense to have all 
>>>> subprotocol-specific attributes registered there.
>>>>
>>>>> An alternative might be to only add such a new SDP attribute to 
>>>>> the generic IANA SDP attribute registry (which probably would be 
>>>>> done anyhow). I assume that the generic SDP attribute registry 
>>>>> would also refer to the document introducing this new attribute.
>>>>>
>>>> Either would work, however my preference would be a complete 
>>>> listing of attributes that have subprotocol specific meaning.
>>>>
>>>> I'd be interested in what other people think though
>>>
>>> From looking at the existing IANA registry 
>>> http://www.iana.org/assignments/sdp-parameters/sdp-parameters.xhtml
>>>
>>> It feels like we should take the approach for att-field (source 
>>> level) and define att-field (data channel).
>>>
>> Thanks for the feedback Christian. Just to be clear: We would need to 
>> allow for multiple entries per attribute, since different 
>> sub-protocols could each define sub-protocol specific behavior for an 
>> attribute.
>>
>> Thanks
>>
>> -- Flemming
>>
>>
>>> Regards, Christian
>>>
>>>>
>>>>
>>>> Thanks
>>>>
>>>> -- Flemming (with my individual hat on)
>>>>
>>>
>>> .
>>>
>>
>
>
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