Re: [MMUSIC] [Technical Errata Reported] RFC5576 (7544)

[Christer Holmberg <[e-mail]>]

Hi Harald,

I am not sure I understand your comment, nor the comment from Philipp. They
seem to be related to some implementation, because I have no idea what you
refer to when you say "members", "set", "count" and "field" :)

Are there implementations that add multiple instance of the same ssrc-id value 
to the sscr-group attribute?

Regards,

Christer

-----Original Message-----
From: mmusic <[e-mail]> On Behalf Of Harald Alvestrand
Sent: Monday, 19 June 2023 21.25
To: [e-mail]
Subject: Re: [MMUSIC] [Technical Errata Reported] RFC5576 (7544)

The actual case where it did not go well was a case where the members were
internally represented as a set, but where the count was taken from the field.

The code added two elements, and then removed two elements - when removing the
second element, there was no such member in the set any more.

(Not the exact code, but illustrates the prinicple)

This violates the Principle of Least Astonishment. We shouldn't violate that.

On 6/16/23 03:18, Christer Holmberg wrote:
> Why would someone use something like a=ssrc-group:FID 1234 1234? And,
> even if someone does, what error would it cause?
>
> Also, we don't have similar text for e.g., the SDP group attribute.
>
> Regards,
>
> Christer
>
>
> -----Original Message-----
> From: mmusic <[e-mail]> On Behalf Of RFC Errata System
> Sent: Thursday, 15 June 2023 21.37
> To: [e-mail]; [e-mail]; [e-mail];
> [e-mail]; Francesca Palombini
> <[e-mail]>; Bo Burman
> <[e-mail]>; [e-mail]
> Cc: [e-mail]; [e-mail]; [e-mail]
> Subject: [MMUSIC] [Technical Errata Reported] RFC5576 (7544)
>
> The following errata report has been submitted for RFC5576,
> "Source-Specific Media Attributes in the Session Description Protocol
> (SDP)".
>
> --------------------------------------
> You may review the report below and at:
> https://www.rfc-editor.org/errata/eid7544
>
> --------------------------------------
> Type: Technical
> Reported by: Philipp Hancke <[e-mail]>
>
> Section: 4.2
>
> Original Text
> -------------
> Every <ssrc-id> listed in an "ssrc-group" attribute MUST be defined by
> a corresponding "ssrc:" line in the same media description
>
> Corrected Text
> --------------
> Every <ssrc-id> listed in an "ssrc-group" attribute MUST be defined by
> a corresponding "ssrc:" line in the same media description and MUST
> appear only once in this ssrc-group
>
> Notes
> -----
> The goal is to clarify that something like
>    a=ssrc-group:FID 1234 1234
> is not valid. While this is demuxable (in the BUNDLE sense) it would
> require chaining of ssrc-demuxing and payload type demuxing which is a
> lot of complexity.
> The uniqueness is already implied by the following sentence (emphasis
> is
> mine):
>     The SDP media attribute "ssrc-group" expresses a relationship
> among
> *several* sources of an RTP session earlier in the section.
>
> Instructions:
> -------------
> This erratum is currently posted as "Reported". If necessary, please
> use "Reply All" to discuss whether it should be verified or rejected.
> When a decision is reached, the verifying party can log in to change
> the status and edit the report, if necessary.
>
> --------------------------------------
> RFC5576 (draft-ietf-mmusic-sdp-source-attributes-02)
> --------------------------------------
> Title               : Source-Specific Media Attributes in the Session
> Description Protocol (SDP)
> Publication Date    : June 2009
> Author(s)           : J. Lennox, J. Ott, T. Schierl
> Category            : PROPOSED STANDARD
> Source              : Multiparty Multimedia Session Control RAI
> Area                : Real-time Applications and Infrastructure
> Stream              : IETF
> Verifying Party     : IESG
>
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