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1. Re: Token Bucket Algorithm
mrmoneymatters Apr 27, 2013 11:32 AM (in response to mrmoneymatters)ok, I think I figured out how to solve for Bc but does Be always equal Bc? I can't seem to figure out how to solve for Be...
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2. Re: Token Bucket Algorithm
Annamalai Apr 27, 2013 12:10 PM (in response to mrmoneymatters)Hello Frnd
Shape traffic on DLCI to 256kbs & frame-relay cir 256000
Solution: 256 * 1000 = 256000 bits/s. The CIR is listed in bits/s.
frame-relay bc 2560
Solution: Bc = CIR in Kbps * Tc.
Bc = 256 * 10 => 2560
frame-relay be 2560
Solution: Be = [Access Rate - CIR ] * Tc/1000 Note: Access Rate and CIR are in b/s
Be = [512000 - 256000 ] * 10/1000
= [256000] * 1/100
= [256000]/100
= 2560
HTH
Annamalai
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3. Re: Token Bucket Algorithm
Dante Apr 28, 2013 10:19 AM (in response to mrmoneymatters)Some official explanation
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/WANQoS.html#wp97266
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4. Re: Token Bucket Algorithm
fracjackmac May 28, 2013 11:56 PM (in response to mrmoneymatters)Dante's link provides a lot of good information, but the simpler document found here provides a more direct approach to the problem: www.cisco.com/warp/public/125/21.pdf
A formula for the time interval in terms of committed burst is provided: Tc = Bc/CIR. The document also indicates that Bc (and Be) is expressed in bits, Tc in seconds, and CIR in bits per second.
You can rearrange this formula to determine committed burst: Bc = Tc * CIR. As long as your units match up, it's easy to determine the correct value for Bc.
Given a CIR of 256 kbps and a Tc of 10 ms:
1) Convert 256 kbps to 256000 bits per second.
2) Convert 10 ms to .01 seconds
3) Do the math: Bc = 256000 * .01 = 2560
Since you are told to allow bursts up to 512 kbps, the DLCI's peak rate, you first need to determine your excess information rate (EIR) in order to determine Be [ Peak = CIR + Be/Tc per the document; therefore, EIR = Be/Tc ].
EIR is defined as Burst Rate (Peak Rate) minus CIR so your excess information rate is 512 kbps - 256 kbps = 256 kbps.
Rearranging the formula EIR = Be/Tc to solve for Be, you get Be = EIR * Tc. Like the calculation for Bc, EIR should be in bits per second and the time interval should be in seconds. Noting that Tc remains the same, you get the same result as Bc.
Given an EIR of 256 kbps and a Tc of 10 ms:
1) Convert 256 kbps to 256000 bits per second.
2) Convert 10 ms to .01 seconds
3) Do the math: Be = 256000 * .01 = 2560
Keep in mind that if your burst rate were 768 kbps while your CIR and time interval remained unchanged, your Be value would be 512000 * .01 = 5120.