CAR, or Committed Access Rate, is a fairly recent addition to Cisco IOS. It first appeared on high-end boxes in the 11.1.CA train, and has been added to the low end boxes in the 12.0 train.
CAR combines traffic prioritization, policing, and monitoring. The one thing it will not do is traffic shape. Generic Traffic Shaping is still your best bet if you need to shape traffic.
The difference between traffic shaping and traffic policing lies in what happens when more than the allotment of data is sent. With traffic shaping, extra packets are buffered and dribble out according to the rate specified. A policing method like CAR may elect to simply drop excessive packets, or lower their priority, but it will not buffer them.
CAR policing example
CAR prioritizing example
CAR monitoring example
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Priority Queuing Alternative
