3560 Policer Burst Value

I am having a real hard time finding good information on this topic for use
in the real world. In the lab, we would usually just configure the burst
size we are told on a Cat 3560. I have done a LOT of reading on it, and
there are a lot of conflicting stories with regards to this.

Basically, I am trying to find out how to calculate an optimal burst value
on a 3560 QoS policy doing policing. As you probably know the syntax looks
like this:

police [rate in bits/s] [burst size in bytes]. Remember, this is policing
not shaping so the classic shaping formula of tc = bc/cir has no relevance
here mainly because the token refresh rate is not based on a static set
amount of time. The burst size is actually the size of the token bucket
itself in bytes, not a rate of any kind and it is filled as a function of
the policed rate and the packet arrival rate. The refill rate of the bucket
is not based on a static amount of time like in FRTS for example. It
basically says "how long was it since the last packet...multiply that times
the policed rate, and divide by 8 to give me bytes". In other words it
pro-rates the tokens. Makes sense.

Anyways...I have found 2 sort of "methods" to calculating this, but they are
so far off from one another I am not quite sure which one to use in the real
world.

Method 1: The classic CAR formula we see on routers: (rate * 1.5) / 8.
This basically gives you 1.5x the policed rate, and converts it to bytes.
Makes sense.
Method 2: 2x the amount of traffic sent during a single RTT.

In my case, I am trying to police a video conferencing endpoint to 3Mbps so
by method 1 that gives me a burst size of 562,500 bytes. Using method 2,
let's just say I have an average RTT of 100ms. That method would yield a
burst size of 75,000 bytes. That is a HUGE difference

This came about because the video endpoint was dropping frames. I noticed
the policed rate in the policy was 3,000,000 but the burst size was 8000
bytes (the lowest possible value). When I changed the burst based on a
100ms RTT and the above formula the problem went away, but now I am having
doubts on the proper value to use here.

Does anybody have any insight on how to actually calculate this properly?

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net