Subject: [xrblock] Per RTP stream metric (Per SSRC metric)

From: Qin Wu <[email-masked]>
Date: Tue, 22 Nov 2011 21:27:47 +0800

I believe most of the existing published XRBlock work and most of the new XRBlock work 
we are working on are all per RTP stream metric. The typical use cases we have based on 
RFC3550 and RFC6285 are listed below:

Simple Multicast Audio Conference Use Case
Each conference participant use audio conference application to send
its own audio data in chunks with 20 ms duration. Each chunk of audio data
is preceded by an RTP header. The SSRC in the RTP header will be used to
identify each chunk belonging to the same participant. The receiver will also 
use SSRC in the RTP header to group all the audio data together into one RTP 
stream.

Layered Encoding Use case

Many implentaion use multimedia applications to adjust transmission rate,
in order to satisfy different bandwidth requirements of heterogeneous receivers,
it is more desirable to place the rate adaptation at the receiver. In such case, 
the source transport each layer of data in different RTP stream. If there is 
multiple sources for layered data destined for the same receiver, each source 
transport each layer of data in different RTP session.

Audio and Video Conference Use Case

In a teleconference composed of audio and video media encoded separately, each medium
SHOULD be carried in a separate RTP session with its own destination
transport address. One motivation for this separation 
is to allow some participants in the conference to receive only one medium
if they choose. In this case, a user participating in both sessions should 
use the same CNAME in the RTCP SDES packets for both so that the sessions 
can be associated.

RAMS Use case

In RAMS Use case, When an RTP receiver requests the Reference Information from the
retransmission server, it can opt to rapidly acquire a specific
subset of the available RTP streams in the primary multicast RTP
session.  Alternatively, the RTP receiver can request the rapid
acquisition of all of the RTP streams in that RTP session.
if the RTP receiver wants to rapidly acquire multiple RTP sessions
simultaneously, separate unicast RTP sessions will be established for
each of them.

Regards!
-Qin