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Forum Replies

  1. Hi Davis,

    It depends what you want to achieve.

    For example, the ISP will probably use policing since they don’t want to waste resources to buffer customer packets exceeding traffic.

    The customer however probably doesn’t want packet drops so they will configure shaping to match the rate that the ISP polices at.

    Also keep in mind that shaping adds delay so it’s not a good idea to use this for realtime traffic like VoIP.


  2. Hi Muhammad,

    Policing is typically implemented by ISPs to limit the traffic of their customers so it will depend on the traffic contract that they sell you.

    The single rate two color policer might be a bit unfair since it doesn’t allow bursting. With a CIR of 128kbps then you’ll only be able to reach 128kbps if you keep sending traffic non-stop.

    The single rate three color policer allows bursting. Since data traffic is “bursty” by nature, this is probably a bit more fair to use. When your connection is idle, you can accumulate up to the Be and spend your Bc+Be when required.

    The Dual rate three-color policer is useful when the ISP is selling more bandwidth than they actually can offer. It’s very unlikely that all customers are sending at maximum capacity all the time so they can offer you a “dual rate” contract. You might pay for a CIR of 128kbps and go up to 256kbps when the network is underutilized.


  3. Hi Rene,

    How actually we calculate the BC and BE base on the CIR. What is the standard we should set?

    Is the calculation below correct?

    CAR (Police) formula:
    Bc = CIR / 8 * Tc           (Default Tc = 1.5 seconds)
    Be = 2 * Bc


  4. Hi Rawa,

    I answered the first question a bit above this post.

    Here’s a configuration example for all types btw:

    Policing Configuration Example

    The dual-rate three-color policer will always check both buckets. It will try to take tokens from both buckets, if possible then the traffic is conforming. If the BC bucket is empty but the PIR bucket still has tokens then the traffic is exceeding. Keep in mind the PIR bucket is larger than the BC bucket.


  5. Hi Andrew,

    I still have some doubt

    Let say BC = the total token can be store, if let say the police cir 128kbps, and by default bc=cir/32 which is 4000 bytes.

    and every second refilled the token 128000/8 = 16000 bytes, but the BC is only can fill up max 4000 bytes?

    Then how the user can get 128kbps if the BC token(4000 bytes) is less than the CIR (16000 bytes)?


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