From: Colin Barber (Colin.Barber@xxxxxxxxxxxxxx)
Date: Sun Aug 25 2002 - 17:39:39 GMT-3
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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