Traffic shaping and policing terminology

Bosefus

Was going over traffic shaping an policing and I am not grasping the command syntax.
Traffic policing

What exactly is the difference between the cir and pir? The example the ont command guide gives is

police cir 200000 bc 10000 pir 700000 be 10000 conform-action transmit exceed-action set-prec-transmit 2 violate-action drop.

The book then states that this creates a 200kbps forwarding rate with policing with a 10kbps burst and also configures a pir rates of 700kbps with a 10kbps burst.

I do not understand why there are two separate data rates, why not just make a 900000 data rate with a 20k burst from the get go?

Also, with traffic shaping, what is the difference between burst size and excess burst?

Book states:
bit-rate is the rate that traffic is shaped into
burst size is sustained number of bits that can be set per interval.
excess burst size max bits that can exceed burst size in the first interval of congestion event.

This really confuses me, I would think that anything that goes over the bit rate is shaped/buffered. However from the books definition of commands it appears that the burst-size actually sets the point at which traffic will be shaped and I do not understand how the excess burst comes into play at all.

The command the book gives as an example is

traffic-shape rate 25000 4000 8000

Any help would be greatly appreciated.

Thanks

Bosefus

After much googling I found the answers to the bottom half of my question about excess burst:

Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.2 - Policing and Shaping Overview - Cisco Systems

Tokens are inserted into the bucket at the committed rate. The depth of the bucket is the burst size.

•Average rate. The average rate determines the long-term average transmission rate. Traffic that falls under this rate will always conform.

•Normal burst size. The normal burst size determines how large traffic bursts can be before some traffic exceeds the rate limit.

•Excess Burst size. The Excess Burst (Be) size determines how large traffic bursts can be before all traffic exceeds the rate limit. Traffic that falls between the normal burst size and the Excess Burst size exceeds the rate limit with a probability that increases as the burst size increases.

However I still have not been able to find any answers to the first half of my questions about cir and pir.

I will continue to look, but any input would be very helpful.

Thanks

Bosefus

This cleared up the pir and cir thing:

Understanding the “shape peak” command - CCIE Blog

Basically, with cir and pir you are manually configuring both token buckets as opposed to just 1.

I do not see the point of this other than the example that blog gave.

Tags for search engine.

pir cir traffic shaping traffic policing rate limit car gts