QoS for Tripleplay

Unanswered Question
Aug 31st, 2007

Can someone give me some guidelines on how to best define CIR, Bc and Be when configuring policing. I've read several books and articles on policing and shaping and they all tell how to configure it but I can't find anything that tells how to calculate the values for CIR, Bc and Be. If I have a 10Gig link and want to run Voice, Video and Data across the link, how do you figure what values are best when configuring policing?

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swaroop.potdar Sun, 09/02/2007 - 22:45

For configuring shaping you can use the formula TC=BC/CIR.

And for policing you can use the formula as below.

Normal Burst = Configured Rate * (1 byte)/(8 bits) * 1.5 seconds

Extended Burst = 2 times Normal Burst.

Do note that the policer uses the normal and extended bursts to ensure and meet the committed rate which is your CIR. Lower values in the burst can punish your traffic to soon and give less than required throughput and vice versa.

This should be a good reference link to start with.

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a0080465b25.html

HTH-Cheers,

Swaroop

Joseph W. Doherty Fri, 09/07/2007 - 15:15

For Voice and Video, policing isn't a good thing. Where you could use policing is on Data; the idea being to restrict Data's bandwidth usage to meet the demands of Voice and Video.

Another way of mixing Voice, Video and Data is to guarantee Voice and Video have what they need to operate when then need it at the expense of Data. This usually is accomplished via different queues for the three types of traffic that are scheduled differently.

Although both approaches allow Voice and Video to operate successfully, the major difference is policing doesn't allow data to utilized bandwidth not being used by Voice and Video.

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