Re: [MMUSIC] [rtcweb] Text proposal for Bundle regarding Associating RTP/RTCP With Correct SDP Media Description

Justin Uberti <> Sat, 11 March 2017 00:31 UTC

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From: Justin Uberti <>
Date: Sat, 11 Mar 2017 00:31:42 +0000
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To: Christer Holmberg <>, "Cullen Jennings (fluffy)" <>, Magnus Westerlund <>
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Cc: "" <>, RTCWeb IETF <>, "mmusic \(E-mail\)" <>, "" <>
Subject: Re: [MMUSIC] [rtcweb] Text proposal for Bundle regarding Associating RTP/RTCP With Correct SDP Media Description
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The new jsep-19 draft
<> incorporates the
outcome of said PRs. Please take a look at the new Appendix C.

On Thu, Mar 2, 2017 at 4:49 AM Christer Holmberg <> wrote:


Where are we on this? I see Cullen¹s pull requests, but I don¹t think
think there are many agreements. Or?



On 15/02/17 15:09, "Cullen Jennings (fluffy)" <> wrote:

>To try and help get you text merged in, I separated your text up into a
>bunch of PRs so that the diffs were all clear and each PR tried to deal
>with one issue. There are all in github now and commenting on theses
>would probably be the easies way to get to some combined text.
>> On Feb 14, 2017, at 7:20 AM, Magnus Westerlund
>><> wrote:
>> Hi,
>> Thanks for the feedback. Sorry for my delay in responding, a cold have
>> kept from work.
>> Den 2017-02-02 kl. 23:19, skrev Cullen Jennings (fluffy):
>>> So I much prefer the current text and think there are a bunch of
>>> problems with this text. If we actually had emails explaining what
>>> problems in the current text this was trying to fix, with individual
>>> PRs for those, this would be much easier to resolve each of them and
>>> get them fixed.
>>> 1) we have been trying to avoid the use of "RTP session" as it has
>>> been very unclear to implementors what it is. I think this would be
>>> better if we could rephrase to not use that
>> Okay, but the RTP session is very easy to make clear in the context in
>> of BUNDLE, where this text is intended to be. I can improve that.
>>> 2) both the proposed and current text seem lacking in dealing with
>>> multiple bundle groups
>> Okay, that can be fixed by clarifying that each bundle group results in
>> its own RTP session, thus the procedures in this is per bundle group.
>>> 3) Stats are typically maintained by things after the packet is
>>> routed - not before.
>> So this comes a question of ones view of RTP stack and the question of
>> layering. And this is exactly why I think the current text is
>> problematic. It takes one very particular view, why I attempted to be
>> much more neutral on which order things happens. There are a number of
>> functions that are in the RTP protocol layer, not in the higher layers.
>> There are however some things, like XR VoIP metrcis that are metrics in
>> the higher layers. So, yes this is not clear cut. I think ones view of
>> this depends on if one have a very integrated RTP implementation, then
>> what you say makes sense, but if one has a very layered and modularized
>> design, then my viewpoint makes more sense.
>> From my perspective the most important thing here is that this text if
>> it contains any RFC 2119 words can't prevent some possible
>> implementation choices of the RTP stack.
>>> 4) Need to explain how the SDES in compound RTCP causes updates
>> I can attempt to clarify this. However, there is a potential issue here
>> in that some implementations may not be able to force the receiver to
>> process the content of the SDES RTCP packet prior to some or even all
>> the other RTCP packets in a compound packet.
>> What in the current text:
>>    On reception of any compound RTCP packet prior to dispatching the
>>    received information and data, if there is an RTCP SDES packet
>>    included that SHOULD be processed first.  If that SDES packet
>>    contains SDES MID entries, this can results in updates and additions
>>    to the RTP stream to "m=" line mapping table.  Thus each of the SDES
>>    MID items are processed and the current table entries are checked if
>>    the corresponding MID value matches the current RTP stream to "m="
>>    line mapping, else the entry is updated.  If there is no RTP stream
>>    to "m=" line table mapping entry for the received SDES item's SSRC,
>>    such an entry is created.  Note, that in the process of updating the
>>    table entries, update flap suppression as discussed in Section 4.2.6
>>    of [RFC7941] should be considered.
>> Is insufficient in that regards. Is it only the placement prior to the
>> individual RTCP packet types that is the issue? Should with the
>> exception of the first sentence be moved under the SDES text?
>>> 5) given this removes the outgoing SSRC table, not clear how it
>>> routes RTCP reports. I think this needs to be clarified.
>> Okay, I think I understand that. I have an implicit assumption that the
>> implementation knows how its local (outgoing) RTP Streams are related to
>> the media sources and thus the related RTPsender. I can update the text
>> to address this.
>>> 6) I don't think most implementers are going to have a clue what to
>>> do for the "Third Party Targeted Reports or Feedback" section
>> I can understand that, but I think it is important to call out that this
>> bucket do exist, and if you don't know what to do I think it is fine to
>> ignore these.
>>> I will try and take your PR and break it up into some bit size pieces
>>> so we can try and see if we can get the easy ones out of the way and
>>> focus on the parts that are key changes.
>> Ok, I have seen that you generated a lot of individual issues, I will
>>attempt to look through them and comment if there are things that was
>>unintentional or where I have additional aspects to add.
>> I intend to update my PR based on the feedback I received.
>> Cheers
>> Magnus Westerlund
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