Subject: [AVT] RTP: control traffic adds to session bandwidth

From: Stephen Casner <[email-masked]>
Date: Tue, 7 Jan 2003 15:35:49 -0800 (PST)

Magnus Westerlund pointed out that the text in Section 6.2 of the RTP
spec regarding session bandwidth was not clear about whether the
control traffic (RTCP) bandwidth was in addition to or included in the
session bandwidth.  Does this make the answer clear?

                                                        -- Steve

OLD:

   The control traffic should be limited to a small and known fraction
   of the session bandwidth: small so that the primary function of the
   transport protocol to carry data is not impaired; known so that the
   control traffic can be included in the bandwidth specification given
   to a resource reservation protocol, and so that each participant can
   independently calculate its share. It is RECOMMENDED that the
   fraction of the session bandwidth allocated to RTCP be fixed at 5%.
   It is also RECOMMENDED that 1/4 of the RTCP bandwidth be dedicated to
   participants that are sending data so that in sessions with a large
   number of receivers but a small number of senders, newly joining
   participants will more quickly receive the CNAME for the sending
   sites. When the proportion of senders is greater than 1/4 of the
   participants, the senders get their proportion of the full RTCP
   bandwidth.  While the values of these and other constants in the
   interval calculation are not critical, all participants in the
   session MUST use the same values so the same interval will be
   calculated. Therefore, these constants SHOULD be fixed for a
   particular profile.

NEW: (new/changed text marked by ^^^)

   The control traffic should be limited to a small and known fraction
   of the session bandwidth: small so that the primary function of the
   transport protocol to carry data is not impaired; known so that the
   control traffic can be included in the bandwidth specification given
   to a resource reservation protocol, and so that each participant can
   independently calculate its share.  The control traffic bandwidth is
                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   in addition to the session bandwidth for the data traffic.  It is
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   RECOMMENDED that the fraction of the session bandwidth added for RTCP
                                                          ^^^^^^^^^
   be fixed at 5%.  It is also RECOMMENDED that 1/4 of the RTCP
   bandwidth be dedicated to participants that are sending data so that
   in sessions with a large number of receivers but a small number of
   senders, newly joining participants will more quickly receive the
   CNAME for the sending sites.  When the proportion of senders is
   greater than 1/4 of the participants, the senders get their
   proportion of the full RTCP bandwidth.  While the values of these and
   other constants in the interval calculation are not critical, all
   participants in the session MUST use the same values so the same
   interval will be calculated.  Therefore, these constants SHOULD be
   fixed for a particular profile.

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