Re: [xrblock] proposed change to discard draft for the issue:duplication packet discards

Hi,
  ----- Original Message ----- 
  From: Colin Perkins 
  To: Kevin Gross 
  Cc: xrblock@ietf.org 
  Sent: Saturday, August 18, 2012 12:12 AM
  Subject: Re: [xrblock] proposed change to discard draft for the issue:duplication packet discards

  Kevin,

  On 17 Aug 2012, at 18:11, Kevin Gross wrote:
    I don't think it is necessary or appropriate to include this sort of value judgement. What is expensive? What is necessary? At best, this is getting tangential. I support the original wording of Qin's note though I think it should be a separate paragraph and perhaps marked as a note.

  Qin's original wording seems to me to be encouraging duplication. I do not support that, since it does break RTCP statistics if done in the naïve way implied. I'm happy if someone wants to propose a more neutral wording, part-way between my suggestion and Qin's text.

[Qin]: How about rephrasing it as follows:
"
Note that duplicating RTP packets is for robustness or error resilience but may disrupts RTCP statitics.
In order to tackle this, the mechanism described in [draft-ietf-avext-rtp-duplication-00] can be used which
will not cause breakage of RTP streams or RTCP rules.
"
This statement will put as an indepent paragraph as Kevin suggested.

    As for the applicability discussion, what I'm looking for is: how will this information be used by the entity or entities receiving it? It is already clear from the other text in the draft _what_ is being reported. We don't need to repeat that here. What needs to be clarified and justified is _why_ and to _whom_ this information is useful.

    Clearly the information is useful to receivers who may adjust their jitter buffers based on the information. But they can do this internally and I don't see a need for them to transmit the raw information on which they're acting.

    Clearly the information is useful to network managers who may wish to tune or troubleshoot their networks based on this feedback. But isn't SNMP, a more appropriate reporting channel for these purposes?

    To justify RTCP reporting of this information, I think it needs to be demonstrably useful to the sender(s) and other receivers in the session. I personally can't think of a direct use for this information by these entities. If there is one (or two...), that's what I wish to see included in the applicability discussion. If there isn't one, it calls into question the need to finish this work.

  I generally agree, although RTCP is at least potentially appropriate for network management purposes. 

  -- 
  Colin Perkins
  http://csperkins.org/

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