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Re: [MMUSIC] Sending a=rtcp-mux-only w/o a=rtcp-mux

Eric Rescorla <ekr@rtfm.com> Wed, 08 February 2017 01:15 UTC

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References: <CABcZeBPESaiH2wuE8RhcBHKz5h10MjKQ_EBDzcRpoy7mYeaspA@mail.gmail.com> <CABcZeBOY5pNRB=W_Zkqm5gYDMRGb-p7ChYctGRmfw5oGyYk-Pg@mail.gmail.com> <D4BE3D32.17805%christer.holmberg@ericsson.com> <CABcZeBO9j2nRqJduZCaaKJPT7YFNzrgLpKncmkvJ+6R=wjAH_w@mail.gmail.com> <D4BE4DA4.17818%christer.holmberg@ericsson.com> <CABcZeBMnJ5QoRt3id0dOPVZyyQgzNTtccMqt2dm14sedZOOXVw@mail.gmail.com> <D4BF5838.178E0%christer.holmberg@ericsson.com> <CABcZeBP0+OVqN3gC2DFwafoA3ta8HNd1hM=giWnHD+=kcN-1cg@mail.gmail.com> <7594FB04B1934943A5C02806D1A2204B4BFEF197@ESESSMB209.ericsson.se> <CABcZeBPNKMg+Qw8nhJFdy7wbx23v+=uicpTqP5jgEH_J-wpFAw@mail.gmail.com> <CAD5OKxurvALsOs1wuPUid3QG+1f0B3zZAEWjcpFiD2cQHQCJMg@mail.gmail.com> <CABcZeBNCT4g6=YCsur4D=gv8+wmoQzLaDxYhMDC8kSTwk2O5+g@mail.gmail.com> <CAD5OKxtu+4aHhB=Nq21G93vGZ-MCb_iaUG9bLsgiDMj9g+38Ew@mail.gmail.com>
From: Eric Rescorla <ekr@rtfm.com>
Date: Tue, 07 Feb 2017 17:15:00 -0800
Message-ID: <CABcZeBPFGLmtGwsD48621dSGMwYjz87kDiTzmybU_sra9sWTQA@mail.gmail.com>
To: Roman Shpount <roman@telurix.com>
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Cc: mmusic WG <mmusic@ietf.org>, Christer Holmberg <christer.holmberg@ericsson.com>
Subject: Re: [MMUSIC] Sending a=rtcp-mux-only w/o a=rtcp-mux
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It seems like that just moves the load onto everyone else who has to
process both the
case where you have a=rtcp-mux and the one where you do not.

-Ekr

On Tue, Feb 7, 2017 at 4:26 PM, Roman Shpount <roman@telurix.com> wrote:

> Essentially a few test cases less to test.
>
> Regards,
> _____________
> Roman Shpount
>
> On Tue, Feb 7, 2017 at 6:52 PM, Eric Rescorla <ekr@rtfm.com> wrote:
>
>> On Tue, Feb 7, 2017 at 12:38 PM, Roman Shpount <roman@telurix.com> wrote:
>>
>>> I want to be able to send rtcp-mux-only. I see plenty of scenarios where
>>> my solution communicates exclusively with Web browsers. Once they implement
>>> rtcp-mux-only, given the rate with which browsers are updated, I would
>>> like, at some point, stop using rtcp-mux instead of inserting legacy flag
>>> indefinitely.
>>>
>>
>> What resource are you conserving here? It's not exactly consuming a lot
>> of space in the SDP.
>>
>> -Ekr
>>
>>
>>
>> Regards,
>>> _____________
>>> Roman Shpount
>>>
>>> On Tue, Feb 7, 2017 at 3:33 PM, Eric Rescorla <ekr@rtfm.com> wrote:
>>>
>>>>
>>>>
>>>> On Tue, Feb 7, 2017 at 9:40 AM, Christer Holmberg <
>>>> christer.holmberg@ericsson.com> wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> >> We had a long discussion about this, with many different opinions,
>>>>> and it would take some time to
>>>>> >> go through the archive and check everything. But, one opinion was
>>>>> that it IS useful to send the
>>>>> >> attribute, as it indicates support of the mechanism.
>>>>> >
>>>>> > What does the other side do with that?
>>>>>
>>>>> Well, it knows that it doesn't have to include a=rtcp-mux the next
>>>>> time it wants to do mux-only.
>>>>>
>>>>> Obviously, as you suggested in your original e-mail, if we wouldn't
>>>>> allow a=rtcp-mux-only without a=rtcp-mux (alt #4) in an offer to begin
>>>>> with, it doesn't matter.
>>>>>
>>>>
>>>> Yeah, I don't think this is a plausible option.
>>>>
>>>> At this point it would be great to hear from anyone who thinks that we
>>>> should allow
>>>> a=rtcp-mux-only without a=rtcp-mux....
>>>>
>>>> -Ekr
>>>>
>>>>
>>>>>
>>>>> > Is there any precedent for this in SDP?
>>>>>
>>>>> Not anything I can think of.
>>>>>
>>>>> Regards,
>>>>>
>>>>> Christer
>>>>>
>>>>>
>>>>> From: Eric Rescorla <ekr@rtfm.com>
>>>>> Date: Monday 6 February 2017 at 16:32
>>>>> To: Christer Holmberg <christer.holmberg@ericsson.com>
>>>>> Cc: "mmusic@ietf.org" <mmusic@ietf.org>
>>>>> Subject: Re: [MMUSIC] Sending a=rtcp-mux-only w/o a=rtcp-mux
>>>>>
>>>>>
>>>>>
>>>>> On Mon, Feb 6, 2017 at 5:57 AM, Christer Holmberg <
>>>>> christer.holmberg@ericsson.com> wrote:
>>>>> Hi,
>>>>>
>>>>> >>> Following up to myself, I don't think it's sensible for answers to
>>>>> >>>contain a=rtcp-mux-only, because either you accepted mux, in which
>>>>> case
>>>>> >>>all is good, or you rejected it, in which case it was rejected.
>>>>> >>
>>>>> >> While I agree that a=rtcp-mux would be enough in the Answer as far
>>>>> as
>>>>> >>indicating mux is concerned, including a=rtcp-mux-only in the Answer
>>>>> >>does indicate that the Answerer supports the mux-exclusive mechanism.
>>>>> >
>>>>> > I don't see how that's really that useful
>>>>>
>>>>> But what harm does it cause?
>>>>>
>>>>> I don't think that's the standard here. We should only send indicators
>>>>> in SDP when they
>>>>> do something useful.
>>>>>
>>>>> -Ekr
>>>>>
>>>>>
>>>>> Regards,
>>>>>
>>>>> Christer
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Fri, Feb 3, 2017 at 9:38 AM, Eric Rescorla
>>>>> <ekr@rtfm.com> wrote:
>>>>>
>>>>> I have been reading the mux-exclusive document and I'm not sure it says
>>>>> quite what we want. Specifically, S 4.2 says:
>>>>>
>>>>>    When an offerer sends the initial offer, if the offerer wants to
>>>>>    indicate exclusive RTP/RTCP multiplexing for RTP-based media, the
>>>>>    offerer MUST associate an SDP 'rtcp-mux-only' attribute with the
>>>>>    associated SDP media description ("m=" line).
>>>>>
>>>>>    In addition, if the offerer associates an SDP 'rtcp-mux-only'
>>>>>    attribute with an SDP media description ("m=" line), the offerer MAY
>>>>>    also associate an SDP 'rtcp-mux' attribute with the same SDP media
>>>>>    description ("m=" line), following the procedures in [RFC5761].
>>>>>
>>>>> As I understand this text, the offerer may say the following things:
>>>>>
>>>>>  1. No a=rtcp-mux: No muxing.
>>>>>  2. a=rtcp-mux: I am offering RTCP mux
>>>>>  3. a=rtcp-mux-only + a=rtcp-mux: I will only do RTCP mux
>>>>>  4. a=rtcp-mux-only: I will only do RTCP mux (same as #3).
>>>>>
>>>>> I don't think the last of these is sensible. No current implementation
>>>>> will know what to do with a=rtcp-mux-only w/o a=rtcp-mux, so this will
>>>>> result in interop failures. Thus the MAY in the second graf needs to be
>>>>> a MUST.
>>>>>
>>>>> -Ekr
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> mmusic mailing list
>>>> mmusic@ietf.org
>>>> https://www.ietf.org/mailman/listinfo/mmusic
>>>>
>>>>
>>>
>>
>

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