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

[Stephen Casner <casner@acm.org>]

Peter,

> Just for clarification, in Appendix A.7 of RFC 1889 bis Internet draft have
> the following changes been agreed to (or are these changes not required per
> the agreed changes to the RTCP bandwidth modifier Internet draft)?
>
> (1) "RTCP_RCVR_BW_FRACTION = 0.25"
> changed to
> "RTCP_RCVR_BW_FRACTION = rtcp_bw_senders/(rtcp_bw_senders +
> rtcp_bw_receivers)"
>
> and
>
> (2) "senders > 0" removed?

Those changes have logically been agreed, but the edits are not
exactly as you state.  In Section 6.2, the proportion of senders has
been changed from 1/4 to S/(S+R).  In Section 6.3.1 item 1, the
"senders > 0" clause has been removed, and the following text added at
the end:

      As stated in Section 6.2, an RTP profile MAY specify that the
      RTCP bandwidth may be explicitly defined by two separate
      parameters (call them S and R) for those participants which are
      senders and those which are not.  In that case, the 25% fraction
      becomes S/(S+R) and the 75% fraction becomes R/(S+R).  Note that
      if R is zero, the percentage of senders is never greater than
      S/(S+R), and the implementation must avoid division by zero.

In Appendix A.7, the "senders < 0" clause has been removed and the
inequality is changed from "<" to "<=" so that the inequality is
always true when RTCP_SENDER_BW_FRACTION is 1.0:

       if (senders <= members * RTCP_SENDER_BW_FRACTION) {

However, your change (1) above has not been made because I did not
want to make modifications to the extent that would be required to add
rtcp_bw_senders and rtcp_bw_receivers as arguments to the function and
all calls to it.  Instead, I added the following paragraph just before
the rtcp_interval() function:

   These functions would have to be extended for an implementation
   that allows the RTCP bandwidth fractions for senders and
   non-senders to be specified as explict parameters rather than fixed
   values of 25% and 75%.  The extended implementation of
   rtcp_interval() would need to avoid division by zero if one of the
   parameters was zero.

The full RFCs should be released within a few days.

                                                        -- Steve


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