From: Yasser Aly (blackyeyes00@hotmail.com)
Date: Fri Oct 24 2003 - 15:24:43 GMT-3
Hi Brian,
While reading some of the archived posts about FRTS I passed by yours.
You are saying at the end of the post
" At the start of every Tc Bc amount of credits are added to the Bc bucket.
If the bucket has credits left over when the next Tc starts those credits
will cause the Bc bucket to overflow but the overflow credits will be caught
by the Be bucket. The Be bucket can only hold Be amount of credits. If the
Bc and Be buckets are both full the new credits added each Tc will be lost."
But at the very begining of your post u said that " There doesn't appear to
be a limit as to how long Be can continue to build up credits. I've tested
FRTS scenarios where Be credits built up over 10 minutes (CIR =16000 and Be
= 12000000)." Doesn't this contradict from the previous statement that Be
has a limited size, if it was full and extra Bc overflowed they will be lost
and not added to Be ?
Would u kindly elaborate this more to remove my confusion.
Best Regards,
Yasser
>From: "Brian Dennis" <brian@labforge.com>
>Reply-To: "Brian Dennis" <brian@labforge.com>
>To: <ccielab@groupstudy.com>
>Subject: Frame-Relay Traffic Shaping "Be" Value
>Date: Thu, 24 Apr 2003 17:00:19 -0700
>
>After testing FRTS I can say that Be can be larger than the previous
>"internal interval" (Tc) and even the previous "interval" (full second).
>There does not appear to be a limit as to how long Be can continue to
>build up credits (aka tokens). This means that Be can hold credits from
>a multitude of previous Tc's and even a multitude of full seconds. I've
>tested FRTS scenarios where Be credits built up over 10 minutes (CIR =
>16000 and Be = 12000000).
>
>For those interested in understanding FRTS let me explain it from the
>perspective a single "bucket" (i.e. Be = 0) FRST configuration and then
>from a dual "bucket" (i.e. Be > 0) FRST configuration.
>
>Let's start off the single bucket explanation:
>
>map-class frame-relay SingleBucket
> frame-relay cir 16000
> frame-relay bc 2000
>
>When we first apply FRTS to an interface (or DLCI) we will start out
>with a single bucket full of credits. Every Tc the amount of credits
>equaling Bc is added to this bucket. When a packet needs to be sent the
>router will check to see if there are enough credits to send the packet
>(1 credit equals 1 bit). If there are enough credits, the router will
>send the packet and removes the amount of credits equaling the size of
>the packet. If there are not enough credits the packet gets "shaped" and
>placed in the FRTS hold queue awaiting enough credits to send the
>packet.
>
>Since this is a single bucket configuration we do not store excess
>credits and theoretically can never send more than Bc amount of bits per
>Tc. If this bucket has credits left over when the next Tc starts these
>left over credits will be lost. This is because at the start of every Tc
>Bc amount of credits are added to this bucket that can only hold Bc
>amount of credits.
>
>In contrast to CAR FRTS will never borrow credits from future Bc's and
>will theoretically never go into debt. This ensures that with FRTS the
>router is always guaranteed to have credits to send every Tc. As a side
>note remember that CAR on the other hand does not really guarantee
>bandwidth. CAR only limits bandwidth.
>
>Now the dual bucket explanation:
>
>map-class frame-relay DualBucket
> frame-relay cir 16000
> frame-relay bc 2000
> frame-relay be 62000
>
>When we first apply FRTS to an interface (or DLCI) we will start out
>with two buckets full of credits. Lets call the first bucket the Bc
>bucket and the second bucket the Be bucket. When a packet needs to be
>sent the router will check to see if the Bc bucket has enough credits to
>send the packet. If it does have enough credits the packet is sent and
>the amount of credits equaling the size of the packet is removed from
>the Bc bucket. If the Bc bucket does not have enough credits the router
>will check the Be bucket. The packet will be sent if there are enough
>credits in the Be bucket and the amount of credits equaling the size of
>the packet will be removed from the Be bucket. If there aren't enough
>credits in the Bc or Be buckets the packet is stored in the FRTS hold
>queue till there are enough credits built up to send the packet.
>
>At the start of every Tc Bc amount of credits are added to the Bc
>bucket. If the bucket has credits left over when the next Tc starts
>those credits will cause the Bc bucket to overflow but the overflow
>credits will be caught by the Be bucket. The Be bucket can only hold Be
>amount of credits. If the Bc and Be buckets are both full the new
>credits added each Tc will be lost.
>
>This is actually my short explanation of FRTS ;-)
>
>Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
>Director of CCIE Training and Development - IPexpert, Inc.
>Mailto: brian@ipexpert.net
>Toll Free: 866.225.8064
>Outside U.S. & Canada: 312.321.6924
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