From: Dan (dans@danbsd.a.la)
Date: Tue May 18 2004 - 14:18:37 GMT-3
But you are talking about FR.
CAR is not frame relay traffic shaping.
When you can do frame relay fragmentation
(http://www.cisco.com/warp/public/788/vofr/fr_frag.html or for short
http://tinyurl.com/254jv ), then small TC will result with the voice
packets getting "through" the big data packets.
But if you dont do frame relay fragmentation, then the big packets wont be
fragmented.
The question is about cisco implementation of car:
1. The router chooses the packet to send and then wait for the bucket to
fill
or
2. The route waits for the bucket to fill and then chooses what packet to
fill.
The first method will result with no advantage for the voice
The second method is very hard to implement - how full the bucket should
be before the router will choose the packeet to send.
You can emulate the frame relay fragmentation with ppp :
http://www.cisco.com/en/US/partner/tech/tk652/tk698/technologies_tech_note09186a0080094660.shtml
or for short : http://tinyurl.com/2gho2
\\\On Tue, 18 May 2004 11:14:05 -0400, John Underhill <stepnwlf@magma.ca>
wrote:
> 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.
>>
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