Re: [MMUSIC] IANA registration of SDP attributes

Flemming Andreasen <fandreas@cisco.com> Tue, 05 April 2016 01:38 UTC

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To: Paul Kyzivat <pkyzivat@alum.mit.edu>, mmusic@ietf.org
References: <56E1C193.1050308@alum.mit.edu> <56E2EF31.2020808@alcatel-lucent.com> <56E2F67D.7060005@alum.mit.edu>
From: Flemming Andreasen <fandreas@cisco.com>
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Date: Mon, 4 Apr 2016 21:37:58 -0400
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Subject: Re: [MMUSIC] IANA registration of SDP attributes
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On 3/11/16 11:46 AM, Paul Kyzivat wrote:
> On 3/11/16 11:15 AM, Juergen Stoetzer-Bradler wrote:
>> Paul,
>>
>> The last alternative would have the advantage that different subprotocol
>> documents could be referenced for the same attribute. Like e.g. for the
>> setup attribute (if there were BFCP over data channel transport specific
>> aspects):
>>
>> *SDP Name*     *Level(s)*     *Reference(s)*
>> accept-types
>>     media,
>> dcsa(MSRP)
>>     [RFC4975]
>> [draft-ietf-mmusic-msrp-usage-data-channel]
>> cat
>>     session
>>     [RFC4566]
>> fmtp
>>     media,source     [RFC4566][RFC5576]
>> mediaclk
>>     session,media,source
>>     [RFC7273]
>> ptime
>>     media
>>     [RFC4566]
>> recvonly
>>     session,media,
>> dcsa(MSRP)
>>     [RFC4566][RFC4975]
>> [draft-ietf-mmusic-msrp-usage-data-channel]
>> setup
>>     session, media
>> dcsa(MSRP)
>> dcsa(BFCP)
>>     [RFC4145]
>> [draft-ietf-mmusic-msrp-usage-data-channel]
>> [draft-schwarz-mmusic-bfcp-usage-data-channel]
>>
>>
>> Therefore I'd be in favor of your last alternative.
>
> Let's see what other comments we get, especially from Flemming.
>

Thanks for putting this together Paul. My preference is also the last 
alternative.

Thanks

-- Flemming

> Then, if this is preferred direction we can work on refining it.
>
>     Thanks,
>     Paul
>
>> Thanks,
>> Juergen
>>
>>
>> On 10.03.2016 19:48, EXT Paul Kyzivat wrote:
>>> [splitting off from the thread on data-channel-sdpneg]
>>>
>>> Currently IANA has five(!) separate registries for sdp attributes:
>>>
>>> att-field (session level)
>>> att-field (both session and media level)
>>> att-field (media level only)
>>> att-field (source level)
>>> att-field (unknown level)
>>>
>>> They all have the same format:
>>>
>>> *Type**
>>> *     *SDP Name**
>>> *     *Reference**
>>> *
>>> att-field (session level)     cat     [RFC4566]
>>> att-field (both session and media level)     recvonly
>>>     [RFC4566]
>>> att-field (both session and media level)     mediaclk
>>>     [RFC7273]
>>> att-field (media level only)     accept-types
>>>     [RFC4975]
>>> att-field (media level only)     fmtp
>>>     [RFC4566]
>>> att-field (source level)     fmtp
>>>     [RFC5576]
>>>
>>>
>>> This format is a pain, because it is hard to look an attribute up if
>>> you don't know at what level(s) it is valid. It also has the potential
>>> to allow an attribute name to be registered for unrelated purposes if
>>> the type is different. (IMO that would be bad.)
>>>
>>> A long time ago (several years now), as part of the 4566bis work, I
>>> proposed that these tables be merged into one. It was my impression
>>> that this was agreed and would be done. But I don't recall any
>>> agreement on the logistics of doing so.
>>>
>>> My thought was that the combined table would look like:
>>>
>>> *SDP Name*     *Level(s)*     *Reference(s)*
>>> accept-types
>>>     media
>>>     [RFC4975]
>>> cat
>>>     session
>>>     [RFC4566]
>>> fmtp
>>>     media,source     [RFC4566][RFC5576]
>>> mediaclk
>>>     session,media,source
>>>     [RFC7273]
>>> ptime
>>>     media
>>>     [RFC4566]
>>> recvonly
>>>     session,media
>>>     [RFC4566]
>>>
>>>
>>>
>>> Then we get to data channel attributes. My thought is to incorporate
>>> them into this table structure, as yet another "level". E.g.,
>>>
>>> *SDP Name*     *Level(s)*     *Reference(s)*
>>> accept-types
>>>     media,dcsa
>>>     [RFC4975][draft-ietf-mmusic-msrp-usage-data-channel]
>>> cat
>>>     session
>>>     [RFC4566]
>>> fmtp
>>>     media,source     [RFC4566][RFC5576]
>>> mediaclk
>>>     session,media,source
>>>     [RFC7273]
>>> ptime
>>>     media
>>>     [RFC4566]
>>> recvonly
>>>     session,media,dcsa
>>>     [RFC4566][RFC4975][draft-ietf-mmusic-msrp-usage-data-channel]
>>>
>>>
>>> (And this could also be extended for websockets if somebody proposes a
>>> way to negotiate attributes for data channels too.)
>>>
>>> Using this format, if you want to know more than the name and the
>>> level(s) at which it can be used you need to consult the references.
>>> And when there are multiple references you don't know which one(s) you
>>> need to consult. This can be "fixed" by including more information
>>> from the reference into the registry. Conversely, we could strip it
>>> down further and remove the levels from the registry - so you need to
>>> consult the references for that too.
>>>
>>> For instance, if we wanted to simplify finding the right reference for
>>> the level you are interested in, we could do:
>>>
>>> *SDP Name*     *Level(s)*     *Reference(s)*
>>> accept-types
>>>     media,
>>> dcsa
>>>     [RFC4975]
>>> [draft-ietf-mmusic-msrp-usage-data-channel]
>>> cat
>>>     session
>>>     [RFC4566]
>>> fmtp
>>>     media,source     [RFC4566][RFC5576]
>>> mediaclk
>>>     session,media,source
>>>     [RFC7273]
>>> ptime
>>>     media
>>>     [RFC4566]
>>> recvonly
>>>     session,media,
>>> dcsa
>>>     [RFC4566][RFC4975]
>>> [draft-ietf-mmusic-msrp-usage-data-channel]
>>>
>>>
>>> Or we could go further, and break the dcsa level down by subprotocol:
>>>
>>> *SDP Name*     *Level(s)*     *Reference(s)*
>>> accept-types
>>>     media,
>>> dcsa(MSRP)
>>>     [RFC4975]
>>> [draft-ietf-mmusic-msrp-usage-data-channel]
>>> cat
>>>     session
>>>     [RFC4566]
>>> fmtp
>>>     media,source     [RFC4566][RFC5576]
>>> mediaclk
>>>     session,media,source
>>>     [RFC7273]
>>> ptime
>>>     media
>>>     [RFC4566]
>>> recvonly
>>>     session,media,
>>> dcsa(MSRP)
>>>     [RFC4566][RFC4975]
>>> [draft-ietf-mmusic-msrp-usage-data-channel]
>>>
>>>
>>> Thoughts?
>>>
>>>     Thanks,
>>>     Paul
>>>
>>>
>>>
>>>
>>> _______________________________________________
>>> mmusic mailing list
>>> mmusic@ietf.org
>>> https://www.ietf.org/mailman/listinfo/mmusic
>>
>>
>>
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>
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