Re: [xrblock] WGLC for draft-ietf-xrblock-rtcp-xr-discardandxrblock-rtcp-xr-discard-rle-metrics

[Varun Singh <[e-mail]>]

Hi Qin,

Comments inline.

Cheers,
Varun

On Thu, Jul 5, 2012 at 5:21 AM, Qin Wu <[e-mail]> wrote:
>>>> 18.Section 5.1, Paragraph 2:
>>>>
>>>> I think XR report is for regular RTCP reporting not used for timely
>>>> feedback.
>>>>
>>>> Therefore I am not sure Discard RLE report can be included in immediate or
>>>> early feedback packets as per RFC4585.
>>>
>>> IMO, the RFC3550 (Section 6.2) rules do not forbid shortening the RTCP
>>> reporting interval.
>>> From RFC3550: The RECOMMENDED value for the reduced minimum in seconds is 360
>>>       divided by the session bandwidth in kilobits/second.  This minimum
>>>       is smaller than 5 seconds for bandwidths greater than 72 kb/s.
>>>
>>> [Qin]: RFC3550 doesn't say you can change timing rule for RTCP XR.
>>> I think XR should follow the same timing rule as RTCP SR/RR.
>>>
>>
>> I meant to say: XR follows timing rules of RFC3550, which allows
>> scaling of reporting interval (it does not allow sending early or
>> immediately as in RFC4585 but allows scaling).
>
> [Qin]: I think the scale level is up to bandwidth allocated for XR and the number of  receiver,
> such scale degree is very limited if the available bandwidth is below miminal level.

Based on my implementation, the reporting interval of RFC4585 over two
consecutive RTCP intervals averages to the RTCP interval of RFC3550.
For example: X marks the instant the RTCP report was sent, in RFC4585,
the RTCP interval following an early report compensates for the early
feedback.

RFC3550: X----------X----------X
RFC4585: X-----X---------------X

However, after re-reading the text in the draft:
      The receiver MAY send the Discard RLE Reports as part of the
      regularly scheduled RTCP packets as per RFC3550.  It MAY also
      include Discard RLE Reports in immediate or early feedback
      packets as per RFC4585.

I do not think the text requires a change:
The text proposes to the implementor that the receiver may send the
RTCP compound packet immediately/early if the two sides support it
else it should use the regular RTCP interval.

>>
>>> So the reporting endpoint should be able to scale the reporting
>>> interval. If this is not possible then how can we do it?
>>>
>>> [Qin]: Big question,:-)
>>>
>>
>> Perhaps someone can clarify if the XRBLOCK can vary the RTCP interval.
>
> [Qin]: I think your should ask how much the XRBLOCK can vary the regular RTCP interval?

Consider an AVPF session which also supports XR report blocks.
If the receiver for whatever reason decides to send the compound RTCP
packet early
then the receiver can add the XR report block to the compound RTCP packet.

I dont see what forbids the endpoint supporting AVPF to not be able to
send XR blocks early.
Especially, since the size of the RTCP report affects the reporting
interval even in RFC4585.




-- 
http://www.netlab.tkk.fi/~varun/