rfi : typical RTCP send rates for VOIP

I'm trying to get info on what the average RTCP send rates etc might be on a typical VOIP network. Some general RTCP figures that I've seen give rates of 12/min. And then there is the RTCP upper bound of "data rate *

I suspect that the answer for VOIP may be somewhere in between.

If anyone can give some ptrs (urls etc) to further info on this topic, I would be very grateful.

Thanks in advance, Steven Perryman