RE: QOS - bandwidth, shape, police

I just questioned that over the weekend. The way I look at it is this:

Bandwidth - Say you do Bandwidth XX but you have Y in total Bandwidth
then you are reserving XX amount in cause of congestion. No congestion
then you get more then XX if it is available.

Police - Hard limit. You do Police XX and that is what you get. Go
over and it drops the extra packets. That traffic acts like as if the
line was now XX instead of Y. Say you have 2000 bytes but the policing
limits it to 1500. Then the 1500 is sent out and the remain 500 is
dropped. Now the host sends to resent that missing 500 a second time.
If you drew it as a Bytes vs time graph it would look very wavy

Shape - Same as police, however if you go over it buffers the
rest(until the buffer is full). Now say you has 2000 bytes you are
sending but shaping has limited it to 1500. In that case the 500 is
buffered. Next time cycle you may only send 1000 bytes so it will tack
on the additional 500 to make a even 1500. That way you have a smooth
output...aka straight line if you use the same chart talked about above.

Hope that helps. If other disagree please let me know.

Rob

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Mark Matters
Sent: Tuesday, September 08, 2009 12:46 PM
To: ccie forum
Subject: QOS - bandwidth, shape, police

I am starting to confuse myself on when to use bandwidth, police or
shape.

Based on question wording who do you know what they are asking you to
do?

Am I right here?
Bandwidth = guaranteed bandwidth
Police = maximum bandwidth
Shape = limit bandwidth

R411(config-pmap)#class thisisgoingtodrivemetodrink
R411(config-pmap-c)#?
QoS policy-map class configuration commands:
  bandwidth Bandwidth
  compression Activate Compression
  drop Drop all packets
  exit Exit from QoS class action configuration mode
  netflow-sampler NetFlow action
  no Negate or set default values of a command
  police Police
  priority Strict Scheduling Priority for this Class
  queue-limit Queue Max Threshold for Tail Drop
  random-detect Enable Random Early Detection as drop policy
  service-policy Configure Flow Next
  set Set QoS values
  shape Traffic Shaping

R411(config-pmap-c)#bandwidth ?
  <8-2000000> Kilo Bits per second
  percent % of total Bandwidth
  remaining % of the remaining bandwidth

R411(config-pmap-c)#police ?
  <8000-2000000000> Bits per second
  cir Committed information rate
  rate Specify police rate

R411(config-pmap-c)#shape ?
  adaptive Enable Traffic Shaping adaptation to BECN
  average configure token bucket: CIR (bps) [Bc (bits) [Be
(bits)]],
                  send out Bc only per interval
  fecn-adapt Enable Traffic Shaping reflection of FECN as BECN
  fr-voice-adapt Enable rate adjustment depending on voice presence
  max-buffers Set Maximum Buffer Limit
  peak configure token bucket: CIR (bps) [Bc (bits) [Be
(bits)]],
                  send out Bc+Be per interval

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