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

Hi Steve,

Stephen Casner wrote:

>>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'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?
>  
>

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 

Multimedia Technologies, Ericsson Research ERA/TVA/A
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Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@era.ericsson.se

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