Re: [payload] draft-ietf-payload-flexible-fec-scheme-14 notes

[Magnus Westerlund <[e-mail]>]

Hi,

In regard to the below.

On 2019-01-03 21:50, Giridhar Mandyam wrote:

There are a couple of substantive changes based on AD review (versus version -13) of which the group should be aware:


  1.  Sec. 4.2.1.  Under the description of the SSRC field, the following requirement was previously a SHOULD:  “"The repair streams’ SSRC’s CNAME MUST be identical to the CNAME of the source RTP stream(s) that this repair stream protects.”


There was actually a reason for this SHOULD. That should likely have been written out explicitly. In case of a RTP middlebox adding FEC to one or more streams it forwards towards to a downstream receiver or other middlebox then it can't use the CNAME of the source stream if there are multiple ones from different sources. Secondly, even if it forwards only from one, that SSRC sending the FEC stream probably shouldn't be required to give the impression that it is the source entity doing this. In some cases RTP middleboxes are considering doing this on behalf of the original source, but not always.

Thus, I am opposed to make this change. I rather add an exception statement after the SHOULD.

The repair streams’ SSRC’s CNAME SHOULD be identical to the CNAME of the source RTP stream(s) that this repair stream protects. An FEC stream that protects multiple source RTP streams with different CNAMEs uses the CNAME associated with entity generating the FEC stream or the CNAME of the entity on whose behalf it perform the protection operation.


Cheers

Magnus Westerlund

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