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

From: Aaron Colwell <[email-masked]>
Date: Thu, 3 Jul 2003 09:46:17 -0700 (PDT)

What is the expected behavior if only a b=RR line is specified and it's
value is greater than 5% of the stream bandwidth. The draft says that if
only one parameter is specified then the value of the other is determined
by subracting the value of the specified parameter from 5% of the stream
bitrate. In the case I have mentioned this would cause a negative
bandwidth to be calculated. That is obviously not valid. Could someone
please clarify what should happen in this case.

Thanks,
Aaron

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: Stephen Casner <[email-masked]>
Date: Thu, 3 Jul 2003 14:18:44 -0700 (PDT)

Aaron,

> please clarify what should happen in this case.

I propose to simply say that the unspecified parameter is zero in that
case.
                                                        -- Steve

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From: Aaron Colwell <[email-masked]>
Date: Thu, 3 Jul 2003 14:50:15 -0700 (PDT)

Steve,

This proposal would work fine if only b=RS is present. This would just
mean that the client would not send receiver reports.

In the case where b=RR is specified that would mean that no sender reports
or BYE packets could be sent. Is that allowed? In the A/V case the client
would not be able to sync the streams because it would never get their
CNAME. I suppose that is the server's fault for not specifying a value
for the sender reports. I guess this brings up another question. Does it
make sense for the RS value to be 0?

Perhaps we could modify your proposal to say, "If only b=RS is specified
and it's value is greater than 5% of the stream bitrate, then RR value is
0. If you need a b=RR line that is greater than 5% of the stream bitrate,
then you MUST supply a b=RS line." We could say that or we could just
make the rule that if you are allocating more than 5% of the stream
bitrate to RTCP, you MUST specify both the b=RR and b=RS lines.

Aaron

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From: Stephen Casner <[email-masked]>
Date: Wed, 9 Jul 2003 14:06:39 -0700 (PDT)

Aaron,

> make sense for the RS value to be 0?

We are talking here about a case where b=RR is specified to be > 5%,
and b=RS is not specified, so RS would be taken to be zero.  However,
your interpretation of the effect of RS=0 is incorrect.  First, both
RS and RR apply to all RTCP packet types that a participant might
send.  Second, as Magnus and I have been discussing on the list, the
"1/4 rule" still applies when RS and/or RR are/is specified, except
that we have corrected it to be the "RS/(RS+RR) rule".  If RS=0, that
simply means that senders do not have any RTCP bandwidth dedicated to
them, instead they share RTCP bandwith equally with all participants.

I have clarified this in the draft now, during the final stages with
the RFC editor.

                                                        -- Steve

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From: Aaron Colwell <[email-masked]>
Date: Wed, 9 Jul 2003 14:19:30 -0700 (PDT)

That makes sense to me. Thanks for the clarifications.

Aaron