From: gladston@br.ibm.com
Date: Wed Nov 17 2004 - 09:06:52 GMT-3
Well, good question, if you allow me to say that.
Following previous discussions, "police cir..." allows us to use two rate three color marker, where (using the token analogy) both token are repleshed independently. That is, if using "police cir 256000 pir 512000", there will be two buckets where the first one will receive 256000 tokens every second and the second one will receive 512000 tokens every seconds. Compare this with the command "police 256000..." where the second bucket will be repleshed only when the first bucket is full. That is, if the rate is 256000, 256000 tokens will be added to the token; if tokens are not used, the first bucket will fill up and the excess tokens will go to the second bucket. We can see the second bucket's tokens in this case as credit that you accumulated because you do not used on the past. So you save on the past and can use now. Differently, with "police cir..." we do not need to save before using the second bucket's tokens.
Make sense?
RFC2698 discuss the Two Rate three color marker
and RFC2697 discuss the Single Rate three color marker
What makes it more confusing is that Cisco refers to the command "police 256000 ... violate-action..." as two rate.
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quoted
Two types of token bucket algorithms are in Cisco IOS Release 12.1(5)T: a single-token bucket algorithm and a two-token bucket algorithm. A single-token bucket system is used when the violate-action option is not specified, and a two-token bucket system is used when the violate-action option is specified.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios123/123cgcr/qos_r/qos_o1g.htm#wp1084068
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Hope we get more feedback on this topic.
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