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

[Harald Alvestrand <[e-mail]>]

On 6/20/23 11:43, Christer Holmberg wrote:
>>> 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?
>> There was one implementation that crashed when someone sent it an ssrc-group
>> with multiple occurences of the same SSRC, yes. Whether this was an attack
>> or a mistake, I don't know.
> It would be nice to know WHY it was sent. Perhaps they think it is a valid
> case, which may also have to be dealt with.

Why does it matter why it was sent?
What we are debating is whether it can be regarded as a protocol 
violation if received.


>
> 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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