From: John Underhill (stepnwlf@magma.ca)
Date: Tue May 18 2004 - 12:14:05 GMT-3
There is a lot of conflicting information on Cisco's site about this, and I
had to wade through a lot of documentation before I could make sense of it
all, (voice config guides seemed to make the most sense). What you have to
do is look at what these parameters are, and originally intended for.. if
you have a T1 line say, it could be that the agreement with your carrier
only agrees to a gauranteed bandwidth of some fraction of this bandwidth
(CIR).. (ar - access rate vs cir - gauranteed bandwidth). BC are the number
of tokens that fill a bucket before being put on the wire. BE are the number
of token credits accumulated for transfers that are less then CIR during an
interval, (TC). Now, the smaller the BC the shorter the interval time
between transfers, and minimizing queing delays for smaller packets, (ie
voice). If you have an average packet of 1500 bytes and a cir speed of 1500
k, you probably want to send about 100 packets per interval in 100 ms
intervals to fully utilize the link.. of course it never works out that
evenly, (and my math might be wrong, I just woke up you know..). But, the
formula is.. cir/8 = bc for data for a tc of 125ms. If you have voice
packets you want a much shorter interval, so they can be put on the wire
faster and avoid queue delay. You are aiming for a TC of 10ms here, so
cir/100 for voice. As for BE, it depends on how you have set the CIR. If the
cir is equal to line speed, there is no point to be, (can not exceed line
speed). If cir is less then line speed, you can burst up to line speed with
accumulated credits, so ar-cir = be. If using voice, you want cir to equal
line speed and so be is again not relevant.
Could be wrong, (someone correct me if I am).. but that is my take on it..
----- Original Message -----
From: "Richard Dumoulin" <richard.dumoulin@vanco.es>
To: "Richard Dumoulin" <richard.dumoulin@vanco.es>; "Ahmed Mustafa"
<ahmed.mustafa@sbcglobal.net>; <ccielab@groupstudy.com>
Sent: Monday, May 17, 2004 8:25 PM
Subject: RE: CAR
> Ah, here is the link that confirms my memory is not so bad
>
> "Cisco recommends the following values for the Normal and Extended Burst
> Parameters.
>
> normal burst = r * 1byte/8bits * 1.5 seconds, where r is configured rate
> extended burst = 2 * normal_burst"
>
> Taken from http://www.cisco.com/warp/customer/cc/pd/iosw/tech/carat_wp.htm
>
> Regards
>
> --Richard
>
>
> -----Original Message-----
> From: Richard Dumoulin
> Sent: martes, 18 de mayo de 2004 2:21
> To: 'Ahmed Mustafa'; ccielab@groupstudy.com
> Subject: RE: CAR
>
>
> Cisco recomendation is to use Tc of 1,5 second and BE=2xBc. So Bc=CIRxTc=4
> Mbpsx1,5s=6000000bits=750000bytes and Be=2xBc= 2x750.000=1.500.000bytes.
>
> --Richard
>
> -----Original Message-----
> From: Ahmed Mustafa [mailto:ahmed.mustafa@sbcglobal.net]
> Sent: lunes, 17 de mayo de 2004 23:24
> To: ccielab@groupstudy.com
> Subject: CAR
>
>
> if the task is to configure CAR with 4MB
>
> by using rate-limit commands,
>
> rate-limit input CIR Bc Be? I am only given one value, what vaules should
> be used for Bc and Be.
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Please help support GroupStudy by purchasing your study materials from:
> http://shop.groupstudy.com
>
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Wed Jun 02 2004 - 11:12:13 GMT-3