From: Robert Rech (rjrech@xxxxxxxxxxxx)
Date: Mon Jul 22 2002 - 10:31:02 GMT-3
Tc is not user settable it is set by BC/CIR. Where CIR is what you would
like the sustained average to hit and BC is the Burst Committed per time
frame. so if you divide BC/CIR this is what gives you Tc. Example
setting CIR to match the slowest port speed of 64k and BC to 8k gives
you 8000/64000 =.125 or 8 time frames per second. Setting CIR to 64k and
BC to 16k gives you 16000/64000 = .25 or 4 time frames per second. The
min Tc is .125 or 8 time frames per second. The smaller Tc the more
granular the result. The other thing to remember is that CIR is not
usually set to the Telco cir this is the mincir setting. CIR is usually
set to whatever you want to set the sustained average at usually the
slower of the 2 port speeds. The Frame Relay Adadtive -shaoing becn
command is used to adapt the sustained rate to congestion. For example
if I have set CIR to the slowest port speed and there is no congestion
it will use full port speed, but if either end begins seeing BECN's they
will slow the output until the BECN's stop. The mincir will set the
minimum level for this so that we always can transmit at Telco CIR or
guaranteed rate.
Try setting the the CIR and BC to different values and then do a sh
frame pvc <xx> and you can see the value for Tc change as you change the
other settings.
Hope this is helpful.
Robert Rech
Senior Network Engineer
Cap Gemini Ernst & Young
Kansas City Service Center
rjrech@cgeykcsc.com
phone (816) 459-4767
fax (816) 459-6767
>>> Tom Young <gitsyoung@yahoo.co.jp> 07/21/02 09:29AM >>>
I am very interested in the calculation of Tc, Could I set
it for a Frame-Relay? Or it should be decided by provider?
And the default is 0.125s in everywhere of the world?
Thanks
--- David Luu <wicked01@ix.netcom.com>
> "Be" should be written in bits, i got carried away
> typing bps at the time...
>
> i said that "Be" is sent out in the FIRST interval
> of EVERY SECOND if
> enough tokens are available...
>
> "burst excess" can be sent out in more than 1
> interval, but it CANT take
> place in the SAME second...assuming a Tc of 125ms
> which gives us 8
> intervals PER second, it can be sent out on the 1st,
> 9th, 17th, etc
> interval, the 1st interval will take place in the
> 1st second, the 9th
> interval will take place in the 2nd second, the 17th
> interval will take
> place in the 3rd second...
>
> now for the Be=(AR-CIR)*Tc...
> assume AR=64kbps, CIR=32kbps, and a Tc of 125ms
> this would make Be = 4kb according to the formula
> you are using
> now do CIR+Be=36kb, remember that Be is sent ONCE a
> second if enough tokens
> are available
> so the max you can send in 1 second is 36kb
> you are not effectively using your
> AR...64kb-36kb=28kb of room to burst
>
> to burst from your CIR to AR you would want to use a
> Be of 32kb
> now CIR+Be=64kb=AR
>
> At 04:33 PM 7/16/2002 -0300, Carlos G Mendioroz
> wrote:
> >Guoqi Cui wrote:
> > >
> > > As I understand CIR and BE are in different
> unit.
> >
> >Yes indeed.
> >
> > > We can not say set BE=32000 bps. BE should be
> in
> > > unit of bits. As for the example, 32000 is the
> extra
> > > link speed to handle extra traffic beyond CIR.
> The
> > > formula to calculate BE is: (AR-CIR)*Tc. Tc is
> one
> > > slot time interval. You can set BE higher than
> > > (AR-CIR)*Tc, what is the use of it? Sinece AR is
> the
> > > maximum rate the link can provide, after
> garantee CIR
> > > only (AR-CIR) left.
> >
> >There is only AR - CIR left but in each Tc!
> >You can use your "excess burst" in many Tc's.
> >
> >As I said in the example, even though you have only
> 4000
> >bits left to transmit above CIR, you can actually
> transmit
> >one full minute at AR given that you have enough
> Be.
> >
> >Please take the time to make the experiment.
> >Or read some book (e.g. Tannenbaum's computer
> metworks)
> >about the dual leaky bucket algorithm. That's what
> it is.
> >
> >Regards,
> >
> > >
> > > As for David, you set BE as 32000bps, this is
> > > different from BE's definition, you give a rate,
> BE
> > > should be in bits.
> > >
> > > --- Carlos G Mendioroz <tron@huapi.ba.ar> wrote:
> > > > David,
> > > > I think this is not quite right, or I am
> > > > misunderstanding you.
> > > >
> > > > To be safe, it is ok to set Be to a value >>
> AR/Tc.
> > > >
> > > > It is my understanding that Be is how much
> data you
> > > > can transmit over
> > > > your CIR,
> > > > as you "eat" burst tokens. But you can eat
> them in
> > > > more than one Tc.
> > > >
> > > > Here an example everyone can run to see the
> > > > difference:
> > > >
> > > > CIR = 32 kbps
> > > > Bc = 4000 b
> > > > Tc = .125 s (automatically computed)
> > > > Be = 1920000 b
> > > > Ar = 64 kbps (Access rate, i.e. clockrate)
> > > >
> > > > This will transmit at 64kbps for one minute
> and then
> > > > drop to 32k.
> > > > Try it with ttcp, send 60 x 8192 bytes, it
> will take
> > > > some 75 seconds...
> > > >
> > > >
> http://www.cisco.com/warp/customer/125/21.shtml has
> > > > more info.
> > > >
> > > > Regards,
> > > >
> > > >
> > > > David Luu wrote:
> > > > >
> > > > > like i said in a previous post...
> > > > > "Be" sends excess data in the FIRST interval
> if
> > > > there are enough tokens, it
> > > > > does not send it in the other intervals
> > > > >
> > > > > take the bottom example...
> > > > > port speed = 64000bps
> > > > > cir = 32000bps
> > > > > mincir = 16000bps
> > > > > bc = 4000bps
> > > > > be = 32000bps
> > > > >
> > > > > first we will start off with "Bc", to get
> "Bc" we
> > > > divide 1 second (1000ms)
> > > > > by the time interval (which is 125ms in this
> > > > case), which is 1000ms divided
> > > > > by 125ms = 8...this gives us 8 intervals, so
> a
> > > > 32000bps cir divided by 8
> > > > > gives us a "Bc" of 4000bps
> > > > >
> > > > > again, "Be" sends excess data in the FIRST
> > > > interval if there are enough
> > > > > tokens, it does not send it in the other
> > > > intervals...to send data at the
> > > > > maximum rate the port can handle, we take
> the port
> > > > speed of 64000bps minus
> > > > > the cir of 32000bps...this leaves us with
> 32000bps
> > > > to send in the first
> > > > > interval...
> > > > >
> > > > > if we were to have a "Be" of 4000bps, the
> max rate
> > > > we can send is cir + be
> > > > > (32000+4000), which equals 36000bps,
> remember that
> > > > "Be" is only sent out in
> > > > > the FIRST interval if there are available
> tokens
> > > > >
> > > > > with a Tc of 125ms, it gives us 8 intervals
> > > > > with a Tc of 10ms, it gives us 100 intervals
> > > > >
> > > > > once again i have to stress this, "Be" is
> only
> > > > sent out in the FIRST
> > > > > interval if tokens are available...with a Tc
> of
> > > > 125ms or 10ms, "Be" will
> > > > > still only be sent out ONE time every second
> > > > (1000ms)
> > > > >
> > > > > hope this clears up any confusion you may
> have
> > > > with "Be" and "Bc"
> > > > >
> > > > > At 01:33 AM 7/16/2002 +0500, Ahmed Mamoor
> Amimi
> > > > wrote:
> > > > > >aaaahhhh !! atleast ur with me...
> heheheeh...
> > > > this is what i have beening
> > > > > >saying but not getting a very difinite
> answer
> > > > from the group why they have
> > > > > >used 32000 as be in power session. if bc is
> > > > multipy by 0.125 then be should
> > > > > >also be multiply by 0.125 ... why 1 sec
> > > > > >
> > > > > >-Mamoor
> > > > > >
> > > > > >
> > > > > >----- Original Message -----
> > > > > >From: Guoqi Cui <guoqicui@yahoo.com>
>
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