Subject: [AVT] Questions regarding unicast RTCP extensions for SSM sessions

From: "Jose Rey" <[email-masked]>
Date: Fri, 26 Oct 2007 17:27:31 +0200

Hi,

I've read draft -13 and have some questions and comments:

1.- While the text in p.5 says:

   "The precise setup and configuration of the media senders and their
   interaction with the Distribution Source is beyond the scope of this
   document ... "
and 

the example given in p. 50, S. 15.3 

   "the Distribution Source also needs to
   relay media traffic from each Media Sender to the receivers and to
   forward (aggregated) feedback from the receivers to the Media
   Senders.  In addition, the Distribution Source relays RTCP packets
                                                  ^^^^^^
   (SRs) from each Media Sender to the other two."
                                ^^^^^^^^^^^^^^^^^
is a bit confusing to me. My questions are a) whether this SR forwarding is mandatory or just an example configuration and b) if so, of what use for Media Senders would be to have the SR of the other Media Senders?, and 3) is this what is meant in S.4 with 'virtual multicast environment'? (see below) I don't understand the motivation, that's all.

  "Distribution Source:
   In an SSM context, only one entity distributes RTP data and
   redistributes RTCP information to all receivers.  This entity
   is called the Distribution Source.  It is also responsible for
   forwarding RTCP feedback to the Media Senders and thus creates
   a virtual multicast environment in which RTP and RTCP can be
   applied."

2.- S 10.2, p. 36 says:

   There SHOULD be exactly one "a=source-filter:incl" attribute listing
   the address of the sender.  The RTCP port MUST be derived from the
                      ^^^^^^
   m= line of the media description.

  I guess 'sender' is the Distribution Source.

3.- In 11.3. I guess when 'source' is written in this section it actually means 'Distribution Source'. If so, the text alternates between 'source' and 'Distribution Source', which is confusing. 

I also found some nits:

N1.- P.4 says:

   "In the Summary Feedback Model the node or nodes performing feedback compute
                                                   ^^^^^^^^^^    
   summary information which is distributed to the members by the
   Distribution Source."

I believe 'receiving' instead of performing is what is meant.

N2.- S 10.1, p. 35 : it seems one bracket "]" got forgotten

   rtcp-unicast:rsi *(SP <processing>:<rtcp-type>])
                                                 ^
Also later below:

              / "rsi" *(SP rsi-rule]  
                                   ^

Thanks in advance,

José  

Panasonic R&D Center Germany GmbH
63225 Langen, Hessen, Germany
Reg: AG Offenbach (Hessen) HRB 33974
Managing Director: Thomas Micke

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