Re: [MMUSIC] FW: [rtcweb] How to signal RTX SSRCs with simulcast

Adam Roach <adam@nostrum.com> Wed, 26 July 2017 16:30 UTC

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To: Bernard Aboba <bernard.aboba@gmail.com>, Bo Burman <bo.burman@ericsson.com>
Cc: =?UTF-8?Q?I=c3=b1aki_Baz_Castillo?= <ibc@aliax.net>, "draft-ietf-mmusic-rid@ietf.org" <draft-ietf-mmusic-rid@ietf.org>, "mmusic (mmusic@ietf.org)" <mmusic@ietf.org>, "draft-ietf-mmusic-sdp-simulcast@ietf.org" <draft-ietf-mmusic-sdp-simulcast@ietf.org>
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From: Adam Roach <adam@nostrum.com>
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Date: Wed, 26 Jul 2017 11:29:54 -0500
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Subject: Re: [MMUSIC] FW: [rtcweb] How to signal RTX SSRCs with simulcast
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Future-proofness.

Recall that the original design here was to give redundancy streams the 
same ID as the stream they're repairing, but there were objections that 
doing so would preclude using the mechanism to talk about redundancy 
streams in SDP if such a need ever arose in the future. So, we allow for 
signaling of these IDs in SDP, but (since as you correctly point out 
there are no concrete use cases at the moment) do not require it.

You seem to think this is a problem. Can you describe a scenario in 
which it causes interop issues or additional implementation complexity?

/a

On 7/26/17 11:21, Bernard Aboba wrote:
> Why would a redundancy RTP stream have an "a=rid" line of its own?  I 
> am struggling to find a use case for this.
>
> On Thu, Jul 6, 2017 at 4:49 AM, Bo Burman <bo.burman@ericsson.com 
> <mailto:bo.burman@ericsson.com>> wrote:
>
>     To follow up on this, I suggest making the following addition to
>     draft-ietf-mmusic-rid:
>
>     ---- AFTER this text in section 4 ----
>
>        An "a=rid" SDP media attribute specifies restrictions defining a
>        unique RTP payload configuration identified via the "rid-id" field.
>        This value binds the restriction to the RTP Stream identified
>     by its
>        RTP Stream Identifier SDES item [I-D.ietf-avtext-rid]. To be clear,
>        implementations that use the "a=rid" parameter in SDP MUST support
>        the RtpStreamId SDES item described in [I-D.ietf-avtext-rid].  Such
>        implementations MUST send it for all streams in an SDP media
>        description ("m=") that have "a=rid" lines remaining after applying
>        the rules in Section 6 and its subsections.
>
>     ---- ... add this proposed, new text ----
>
>        Implementations that use the "a=rid" parameter in SDP and that
>        make use of redundancy RTP streams [RFC7656], e.g. RTP RTX
>        [RFC4588] or FEC [RFC5109][I-D.ietf-payload-flexible-fec-scheme],
>        for any of the source RTP streams that have "a=rid" lines remaining
>        after applying the rules in Section 6 and its subsections, MUST
>        support and use RepairedRtpStreamId SDES item described in
>        [I-D.ietf-avtext-rid] for those redundancy RTP streams. This
>     provides
>        the binding between the source RTP stream and the corresponding
>        redundancy RTP stream, by setting RepairedRtpStreamId value for
>        the redundancy RTP stream to the RtpStreamId value of the source
>        RTP stream. The redundancy RTP stream MAY (but need not) have an
>        "a=rid" line of its own, in which case the RtpStreamId SDES
>     item value
>        will be different from the corresponding source RTP stream.
>
>     ---- End changes ----
>
>     The -simulcast draft would be entirely agnostic to this
>     clarification of "a=rid" and RepairedRtpStreamId usage and thereby
>     transparently allow using redundancy RTP streams with simulcast.
>
>     /Bo
>     (as individual)
>
>     > -----Original Message-----
>     > From: Iñaki Baz Castillo [mailto:ibc@aliax.net
>     <mailto:ibc@aliax.net>]
>     > Sent: den 13 mars 2017 14:43
>     > To: Bo Burman <bo.burman@ericsson.com
>     <mailto:bo.burman@ericsson.com>>
>     > Cc: mmusic (mmusic@ietf.org <mailto:mmusic@ietf.org>)
>     <mmusic@ietf.org <mailto:mmusic@ietf.org>>; Taylor Brandstetter
>     (deadbeef@google.com <mailto:deadbeef@google.com>)
>     > <deadbeef@google.com <mailto:deadbeef@google.com>>;
>     draft-ietf-mmusic-rid@ietf.org
>     <mailto:draft-ietf-mmusic-rid@ietf.org>;
>     draft-ietf-mmusic-sdp-simulcast@ietf.org
>     <mailto:draft-ietf-mmusic-sdp-simulcast@ietf.org>
>     > Subject: Re: [MMUSIC] FW: [rtcweb] How to signal RTX SSRCs with
>     simulcast
>     >
>     > 2017-03-13 14:41 GMT+01:00 Bo Burman <bo.burman@ericsson.com
>     <mailto:bo.burman@ericsson.com>>:
>     > > [BoB] Usage of RepairedRtpStreamId and RtpStreamId are already
>     defined on RTP level by -avtext-rid. If we have
>     > preferences on how to best use them with redundancy RTP streams
>     in general, I suggest we add text to -mmusic-rid
>     > about it. This would be regardless if we go for option A or B,
>     but decided once and for all, thus applicable to RFC 4588 rtx
>     > and FLEX-FEC alike.
>     >
>     > Agreed.
>     >
>     >
>     > --
>     > Iñaki Baz Castillo
>     > <ibc@aliax.net <mailto:ibc@aliax.net>>
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