[MMUSIC] Liaison Statement from 3GPP SA4 on RTCP Bandwidth Negotiation

["Miguel A. Garcia" <[e-mail]>]

3GPP SA4 has sent us an LS on RTCP Bandwidth Negotiation. I copy below 
the text.

We should be able to provide them an answer in a reasonable time frame, 
so please, review it and provide with comments to the list. The chairs 
will compile a reply text.

The original document can be found at the 3GPP web site:
http://www.3gpp.org/ftp/tsg_sa/WG4_CODEC/TSGS4_69/Docs/S4-120810.zip

/Miguel and Flemming
-------

3GPP SA4 uses the RTCP bandwidth modifiers (b=RS and b=RR) to control the 
amount of RTCP bandwidth used in point-to-point VoIP and video telephony 
sessions.  As these parameters were primarily designed for multicast 
sessions, the calculations in section 2 of RFC 3556 apply to the total 
RTCP bandwidth for the session, i.e., total bandwidth for all clients 
sending/receiving RTCP traffic. However, there are no SDP Offer/Answer 
models defined that use these parameters for the negotiation of the total 
RTCP bandwidth for point-to-point sessions.

To clarify this, SA4 is planning to make the following recommendations in 
our specifications:

1.	The RS and RR values included in the SDP offer should be treated as 
proposed values for the session and may be modified by the answerer 
during session negotiation.

2.	When generating the SDP answer, the answerer should include the RR and 
RS values proposed in the SDP offer. The answerer may instead choose to 
include RR and RS values lower than those proposed in the SDP Offer.

3.	The RS and RR values included in the SDP answer should be treated as 
the negotiated values for the session and should be used to calculate the 
total RTCP bandwidth for all terminals in the session.



Actions:
To IETF MMUSIC WG

ACTION: 	SA4 asks MMUSIC WG to review the above recommendations and 
identify if there are any discrepancies with the practices or 
understanding in the IETF.

-- 
Miguel A. Garcia
[phone]
Ericsson Spain