From: Song Mu (songmu@xxxxxxxxx)
Date: Sun Aug 25 2002 - 18:51:58 GMT-3
Here is the official answer form Cisco:
frame relay cir
The average rate you want to send traffic out on a given PVC in bps.
This is generally higher than the guaranteed rate but less than the
access
rate (AR). It equals the guaranteed rate only if:
1.The service provider does not allow you to send above guaranteed
rate.
2.The physical line rate on the interface is same as the guaranteed
rate.
3.There are Voice (voice over IP [VOIP] or voice over Frame Relay
[VOFR]) packets on this PVC, therefore you cannot afford dropped
packets for quality or service.
The value of the CIR is 56000 bps is by default.
frame relay mincir
The actual guaranteed rate obtained from service provider in bps. This
value should be the minimum rate you should drop to in the event of
congestion (dropping below this rate implies you are not getting the
bandwidth you are paying for). In certain cases (listed above) the
mincir and
cir values must be the same. The value of mincir is half of the CIR
value in bps by default.
frame relay bc
The amount of data to send per each Tc interval in bits. Ideally for
data PVCs Bc = CIR/8 so that Tc = 125msec. If we are doing voice on the
PVC, then Bc = CIR/100 is preferable, so that the interval Tc = 10msec
(as voice packets cannot tolerate a longer delay). The value of Bc by
default is the CIR in bits.
frame relay be
The amount of excess data allowed to be sent during first Tc interval
in bits once credit is built up. Configure Be only if the Frame Relay
CIR
value is less than the AR. For PVCs carrying voice packets, the Be must
be set to zero to ensure best possible voice quality. The router only
bursts (Be) when there are tokens in the token bucket. The token bucket
does not accrue tokens unless the amount of traffic being sent out is
less than the CIR. The router can only burst for the first Tc, after
which the token bucket is empty. The value of Be by default is zero
bits.
Song
--- Colin Barber <Colin.Barber@telewest.co.uk> wrote:
> I too have not found a solid resource explaining things. A couple of
> things
> that I would query are:
>
> Your definition of CIR is correct but this maps to Cisco's MINCIR.
>
> 'Anything above this but below AR will have DE set' is not always
> correct.
> It's depends on your agreement with your service provider. You may be
> allowed to burst to a certain limit without DE being set. You may be
> allowed
> to burst to a certain level but DE is set and above that burst level
> everything is dropped. You may not be allow to go over the CIR
> without being
> dropped. It all depends and this is why resources explaining FRTS
> conflict
> so much.
>
> Here's how I see it.
>
> MINCIR is the guaranteed rate you can transfer without any drops. You
> drop
> down to this rate when you notice congestion (BECNs). This is the CIR
> your
> provider sets. Obviously it the frame switch is very congested it
> will have
> to drop packets even within CIR however you cannot control this and
> at this
> point your provider is possibly in breech of his SLA to you.
>
> If your provider allows bursts then this is the BC.
>
> If you provider allows bursts over the BC and marks packets with DE
> then
> this is BE. This may allow up to AR speed or not.
>
> AR is the clock your provider is sending you. Even if you have a
> small CIR
> (256k) being supplied on a T1 it is better to have the clock at the
> full
> 1.544Mbps as this reduced latency compared to a clock of 256Kbps.
>
>
>
> -----Original Message-----
> From: Jim Brown [mailto:Jim.Brown@caselogic.com]
> Sent: 25 August 2002 21:04
> To: ccielab@groupstudy.com
> Subject: I need FRTS help or review
>
>
> Everything I have read about FRTS doesn't seem to clear up the use of
> BE,
> BC, CIR, and MINCIR. I have been unable to locate a solid resource
> explaining the concept with any finality.
>
> I've read most of the relevant Usenet postings on Deja, watched the
> threads
> on groupstudy, scoured CCO, and examined the QOS v1.0 course
> material.
>
> I will throw out my assumptions and let list members either verify or
> shoot
> holes on my take of FRTS.
>
>
> A few definitions up front:
>
> AR is the Access Rate or Port Speed of the connection to the frame
> relay
> cloud. This is the maximum number of bits that can be transmitted to
> the
> cloud.
>
> CIR is the Committed Information Rate. This is the maximum number of
> bits
> the provider promises to transmit. Anything above the CIR and below
> the
> access rate will have the DE bit marked and is eligible for
> discard/drop
> during times of congestion.
>
> Lets take a hypothetical circuit for instance, a port speed of 96Kbps
> and a
> CIR of 64Kbps.
>
> The way I read the documentation, in a Cisco configuration CIR should
> be set
> to the actual provider CIR or 64000. The BE or burst excess should be
> set to
> the difference between the access rate and the CIR. I think BE should
> be set
> to 32000, the difference between 96 and 64.
>
> Here is a brief sample config:
>
> map-class frame-relay TestShape
> frame-relay cir 64000
> frame-relay be 32000
>
>
> The map-class could then be applied to the frame map or the
> interface. I was
> previously under the impression you would set the Cisco CIR to the
> port
> speed and the minCIR to the provider contracted CIR. I don't think
> this is
> really the case?
>
> Here is an example:
>
> map-class frame-relay TestShape
> frame-relay cir 96000
> frame-relay mincir 64000
>
> Comments or suggestions? Is this wrong, why or why not?
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