Frame-Relay Traffic Shaping equation

Unanswered Question
Sep 4th, 2008

Hi all,

Not a difficult question if you know - but i don't so i thought that i'd ask :)

When calculating frame-relay TC what is the formula? I'm getting conflicting information. Is it:

tc = bc/CIR

tc = be/CIR

tc = CIR/bc (or be for that matter)

I know that this is probably more of a Qos issue, but hey, most of us run Qos across a WAN anyway :) Your enlightenment would be greatly appreciated. The reason i ask is that i was just watching some old CBT nuggets and he says that CIR is at the top of the mathematical triangle (with tc x bc underneath), but i wasn't sure of where be fits into this equation.

A colleague says that bc should be at the top of the triangle, but surely Jeremy knows best. Just looking for some clarification.

I have this problem too.
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Giuseppe Larosa Thu, 09/04/2008 - 01:37

Hello ab,

think of tc like the inverse of a sampling rate it is measured in seconds.

in tc seconds up to BC*8 bits are treated as conforming frames.

CIR is a bit rate so it is expressed in Bits/s

Bc is a byte quantity ( byte so must divide by 8 to get bits)

If Bc is small Tc is small too.

So the first formula should be the right one

tc [sec] = Bc/CIR [bits / bits /sec]

Hope to help


Ibbywannit Thu, 09/04/2008 - 01:55

That was a clear and concise answer. Have a 5 from me for your efforts.

Thanks Giuseppe.


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