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

From: "Miguel A. Garcia" <[email-masked]>
Date: Fri, 1 Jun 2012 13:46:01 +0200

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
+34-91-339-3608
Ericsson Spain

---

From: "Roni Even" <[email-masked]>
Date: Fri, 1 Jun 2012 19:03:12 +0300

Hi,
In general it is good to add some text about this case since it is not
addressed in RFC3556 or RFC3264. I do not see any text that claims that
RFC3556 should be used for multicast or broadcast only and not to negotiate
for point to point calls.

I am not sure about the proposed recommendations. My understanding is that
since RTCP unlike RTP is bidirectional channel than the RS and RR values
specify the bw required for all endpoints. If the offer had a value for RS
and RR, I believe that in a point to point call when we have two sender and
two receivers each will get half of the RS and RR bandwidth. 
The offerer in this case will offer what he believes is needed for him to
send RTCP RRs and SRs reports multiply by two so if the answerer thinks he
need less bandwidth he should allow for the offerer to have enough RTCP
bandwidth at least for his sender reports. So I think that answerer should
respond with the same value or possibly higher. otherwise we may need to
define that the RR and RS values in the offer represent the bw that offerer
wants to use and the values in the answer would be the value the answerer
like to use, the total RTCP bw will be the sum of the two values.

Roni Even

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On
> Behalf Of Miguel A. Garcia
> Sent: Friday, June 01, 2012 2:46 PM
> To: mmusic
> Cc: Flemming Andreasen; [email-masked]
> Subject: [MMUSIC] Liaison Statement from 3GPP SA4 on RTCP Bandwidth
> Negotiation
> 
> 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:
> 
> 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
> 
> _______________________________________________
> mmusic mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/mmusic

---

From: Gonzalo Camarillo <[email-masked]>
Date: Tue, 5 Jun 2012 13:58:41 +0300

Hi,

this is the link to the LS in the tracker:

https://datatracker.ietf.org/documents/LIAISON/liaison-2012-05-31-3gpp-mmusic-on-rtcp-bandwidth-negotiation-attachment-1.doc

Cheers,

Gonzalo