From: Robert Rech (brech@kc.rr.com)
Date: Tue Oct 08 2002 - 23:13:15 GMT-3
The thing you may be missing is that CIR = the physical port speed of the
slower speed circuit
say I have a hub site with a 256k port and a remote with a 64k port and a
32k cir
on the hub site
CIR = 64k
mincir=32k
BC =8k
Tc = 8/64 =.125sec or 8 time slots/second
Be = 24k This is because my hub port is capable of 256/8 or 32k per Tc. Bc +
Be = hub port speed {not remote end port speed}
This will allow the hub site to burst to it's full port speed for the first
Tc provided that it has available tokens, this will take advantage of
the Frame switches buffering ability without overdriving the remote end to
the point of dropping to many packets.
Remote side
CIR = 64k
mincir = 32k
Bc = 8k
no Be here cause we are telling it to run at port speed and usually would
turn on adaptive shaping based on BECN's
----- Original Message -----
From: "Paglia, John (USPC.PCT.Hopewell)" <JPaglia@NA2.US.ML.com>
To: <Giveortake@aol.com>; <Svuillaume8@aol.com>; <ccielab@groupstudy.com>
Sent: Monday, October 07, 2002 9:08 PM
Subject: RE: FRTS
> I'm not looking at the Doyle book, but if that is truly what it says, then
I
> have a problem with it as well. It just doesn't make logical sense!!!
> Everyone agrees that Be is data that's 'above and beyond the norm', or
> better put a burst, right? Then how can CIR = the physical port speed??
> Wouldn't that max out the port without Be even coming into play??? Am I
> being too literal???
>
> Here are the rules I play by....
>
> CIR = (Committed Information Rate) - average rate of data that can be
> transmitted over a specific connection for a fixed period of time.
Measured
> in bits per second. Provided.
> Bc = (Committed Burst) - maximum amount of data the network agrees to
> transfer, under normal conditions, over a fixed and specific time
interval.
> Measured in bits per second, usually a multiple of CIR (CIR/Tc).
> Be = (Excess Burst) - maximum amount of data in excess of Bc that the
> network will attempt to transfer, under normal conditions, over a fixed
time
> interval. Measured in bits per second.
> Tc = (Time Interval) - pre-determined unit of time measured in seconds per
> burst. Represented by the formula Tc = Bc/CIR. 10 ms is ideal for
voice,
> can NOT exceed 125 ms.
> MINCIR = By default equals CIR/2
>
> HTH,
> John
>
>
>
> > -----Original Message-----
> > From: Giveortake@aol.com [SMTP:Giveortake@aol.com]
> > Sent: Monday, October 07, 2002 9:27 PM
> > To: Svuillaume8@aol.com; ccielab@groupstudy.com
> > Subject: Re: FRTS
> >
> > If thats what Jeff Doyle says, I say Jeff Doyle is wrong! But then
> > again
> > who am I (dumb guy who failed twice) That may be ok for certain
> > situations,
> > but does not cover all.
> >
> > I don't believe you can make a blanket statement like that listed below.
> > Frankly its just wrong. It may be right in a "specific" scenerio but
> > WRONG
> > for another.
> >
> > CIR = Port physical speed
> > Mincir= CIR ( cir provides by carrier)
> > Bc= remote speed circuit /8
> > Be<= port speed of the remote router
> >
> > Actually I think the blanket statements like this are killing people
from
> > understanding. What we need are a couple good scenerios to demonstrate
> > real
> > life situations such as over subscribing a head end, throttling back to
> > certain transmit rates if BECN's received etc.......... Traffic shaping
> > takes some math and some thought. Not memorize these four lines.
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