Subject: [AVT] Errors in draft-ietf-avt-rtcp-bw-05.txt

From: Magnus Westerlund <[email-masked]>
Date: Fri, 25 Apr 2003 09:06:36 +0200

Hi Steve

I think I have located two errors in the draft. They are located in 
section 5, the example:

1. Isn't the values for RR and RS wrong. I believe they should change 
place. If one reads the text below the values in the audio media block 
should be equal to the default values. That would mean 1.25 % of session 
to RS, which is 800. While RR should be 2400 or equal to 3.75%.

2. This does also concern the text below the example. In my 
interpretation there is difference between including both RR and RS and 
leaving them out while you have the bit-rates equal to the default 3.75 
and 1.25 %. When you have the RR and RS in place the 1/4 active sender 
rule is not in place. While when you don't have them it will be in 
place. Therefore there will be a significant difference in how you 
assign the bit-rate. Also I think that one could clarify this difference.

I hope there is possibility to fix these errors before the publication.

Best Regards

Magnus Westerlund 

Multimedia Technologies, Ericsson Research ERA/TVA/A
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From: Stephen Casner <[email-masked]>
Date: Fri, 25 Apr 2003 11:23:34 -0700 (PDT)

Magnus

> to RS, which is 800. While RR should be 2400 or equal to 3.75%.

You are right, these are swapped.  Thanks for finding this error.

> assign the bit-rate. Also I think that one could clarify this difference.

I'm not sure what point you are making.  Is it that the 1/4 active
sender rule says that the active senders get _at least_ 1/4 of the
RTCP bandwidth but that if RS is specified the active senders would
never get more than that?

It was my intention that the behavior be the same when RS and RR are
specified, or even if just one is specified.  These bw specifiers just
set the two input values to the algorithm.  However, I see that the
document does not make this clear.

Do you think there is a reason that the behavior I inteded will not
work?

> I hope there is possibility to fix these errors before the publication.

I believe so.

                                                        -- Steve

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From: Magnus Westerlund <[email-masked]>
Date: Mon, 28 Apr 2003 08:57:05 +0200

Hi Steve,

>Do you think there is a reason that the behavior I inteded will not

The interpretation of your draft that I and other in 3GPP SA4 have made, 
is that when you use both RR and RS you don't use the 1/4 active sender 
rule. If both the values are specified one simple plugs them in as the 
values for each group. I think there are a good reason for doing this 
interpretation.

1. Unless one disables the 1/4 rule it is impossible to turn off RTCP 
receiver reports in cases where there are more then one 1/4 senders, 
which include the so important 1 to 1 case.
2. It becomes impossible to set unsymmetric RTCP bit-rates in 1-1 cases. 
This would be a problem in for example streaming cases where one might 
desire to control the bit-rate in each direction. This can be especially 
important in use cases over wireless links that need rather good control 
over bit-rate.

So based on these arguments I would suggest that you actually clarify 
the draft in this direction.

Best Regards

Magnus Westerlund