From: Connary, Julie Ann (jconnary@xxxxxxxxx)
Date: Sat Jan 06 2001 - 11:50:44 GMT-3
Hi All,
there have been some requests lately for a good resource on Frame-Relay
CIR, BC and BE.
Try:
Data and Computer Communications by Williams Stallings - Fifth Edition.
ISBN: 0-02-415425-3
It has a 3 page very good explanation on Frame-Relay congestion management.
It has great pictures for those of us who are more graphically oriented.
If you don't have it try a library at a local university or on the Web. You
probably won't
find it in your local bookstore - it's also somewhat pricey as it is
commonly used as a
text book - which is how I got it - used it in my grad school classes.
But quickly -
The definition of BE and BC:
BC - Committed Burst Size - the maximum amount of data that the network
agrees to transfer, under normal conditions over a measurment interval T.
BE - Excess Burst Size - the maximum amount of data in excess of Bc that
the network will attempt to tranfer, under normal conditions, over a
measuremnt interval T.
The quantities Bc and CIR are related. Because BC is the amount of
committed data that may be transmitted by the user over a time T, and the
CIR is the rate at which the commiited data may be transmitted we must have:
T= Bc/CIR
I will not attempt to draw the leaky bucket algorithm graphics here but
simply if - you can transmit at the access-rate of your
line until you have tranferred BC amount of information. At that time
traffic is marked discard eligible. When you have tranferred BC + BE amount
of data, traffic begins to be discarded. If you tranfer at your CIR, then
you never get above BC and you never have a problem.
Another really good source is the ATM Forum standards - since ATM also uses
the leaky bucket algorithm.
In otherwords, the key to understanding traffic policing is understanding
leaky bucket.
Julie Ann
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Julie Ann Connary
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c i s c o S y s t e m s Email: jconnary@cisco.com
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