From: elping (elpingu@acedsl.com)
Date: Fri Sep 20 2002 - 00:41:36 GMT-3
rick:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/qos_c/qcprt4/qcdpolsh.htm
read:
Extended burst is configured by setting the extended burst value greater than
the normal burst value. Setting the extended burst value equal to the normal
burst value excludes the extended burst capability. If extended burst is not
configured, given the example scenario, CAR's exceed action takes effect
because sufficient tokens are not available.
the purpose normal burst size is that this is what your token bucket equals to
look at the formula
normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds
extended burst = 2 * normal burst
see how the configured rate which in your case is 15meg is a function of
:normal burst .
all you are doing here is converting 15meg bits to bytes * a tcp round trip
value.
so you are defining your bucket size...in other words this is how much you can
tranmit in bytes
then if you bucket runs out take some more ...in other words tranmit a little
more
which would be your ( externded burst -normal burst)
example
normal burts = 20 extended burst =20
20 -20 =0
normal burts = 20 extended burst =40
40 -20 =20
there is an exact example of your scenario here
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/qos_c/qcprt1/qcdcar.htm#xtocid10
> This bottom part is great
> > with yours you are giving a little more bandwidth
> > when bc=be there is no bursting ...you are allowing to burst
> but, there is one thing I'm still missing. You are saying if they are equal
> bc=be there is no bursting. Then what is the purpose of normal burst? This
> subject is killing me!
>
> Thanks,
> Rick
> ----- Original Message -----
> From: "elping" <elpingu@acedsl.com>
> To: "Rick" <ccie_2003@hotmail.com>
> Cc: "Ccielab (E-mail)" <ccielab@groupstudy.com>
> Sent: Thursday, September 19, 2002 3:36 PM
> Subject: Re: CAR question for QOS expert
>
> > just remember the different calculation in
> > traffic shaping and policing
> >
> > all calculations stem from these two
> > in you example it really does not limit the speed to 15meg
> > the one below will allow only 15meg
> >
> > rate-limit output 15000000 2812500 2812500 conform-action transmit
> > exceed-action drop
> >
> > with yours you are giving a little more bandwith
> > when bc=be there is no bursting ...you are allowing to burst
> >
> > Rick wrote:
> >
> > > Lets say I want to rate limit a connection to 15Mbs on a 45Mbs
> interface. I
> > > looking a Cisco example and it shows they have the burst normal and
> burst
> > > exceed allowing 2,812,500 bytes. Why must we have the burst statements.
> If you
> > > bought a tiered 15Meg connection from a ISP, aside from frame-relay you
> don't
> > > get any more BW than you pay for right? I'm just trying to relate this
> to
> > > something because I don't understand the burst statements. Can someone
> please
> > > explain. I have read about the token bucket and all, but I'm a litte
> confused.
> > > Here is the syntax of the example I was looking at.
> > > int HSSI 0/0/0
> > > rate-limit output 15000000 2812500 5625000 conform-action transmit
> > > exceed-action drop
> > > ip add 10.1.0.9 255.255.255.0
> > >
> > > On a side note, How does one remember all this QOS stuff..??? I guess
> the
> > > trick is once you learn it you must know where to reference it on the
> DOC CD.
> > >
> > > Thanks and Good Luck to all!
> > > Rick
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