[e2e] Control traffic: how many % of payload traffic?

[Michael Welzl]

Hi all,

To achieve scalability, it seems reasonable to restrict the amount of
control traffic which is related to a payload traffic stream by a fraction
of the payload traffic: this way, the overall control traffic remains a
fraction of the related payload traffic no matter how many senders there
are.

For Internet traffic, it may also make sense to restrict control traffic by
the amount of packets, so not only traffic forwarding but also per-packet
header processing is taken into account. So a rule should probably be:

control traffic = min (x % of payload traffic, every yth payload packet)

The values x and y must be predefined (if a single sender exceeds a certain
x or y, the concept won't work).

My question is: how do I come up with appropriate values for x and y?
The answer is probably a trade off between wasted bandwidth and processing
cost vs. gain from control traffic; but these things are very hard to
quantify.
For instance, how did the AVT working group come up with the value of 5% for
RTCP traffic?