From: Robert Rech (rjrech@xxxxxxxxxxxx)
Date: Mon Aug 26 2002 - 12:00:33 GMT-3
Cisco terminology is a bit confusing.
CIR is not carrier committed rate that is mincir.
CIR is the rate you want the circuit to run at until congestion is
encountered.
CIR and mincir are average rates.
BC is the burst committed rate and is for each time interval {Tc}.
Tc is dependent on BC/CIR so if BC = 7000 bits per interval and CIR
{the normal rate} is 56000 bits/sec then Tc = 7000/56000 or 125 us which
gives you 8 time intervals per second.
Be is the amount over BC than can be transmitted in the first time
interval provided there are tokens available.
Suppose you have a hub site with a 512k port and a remote site with a
56 k port the CIR for the PVC is 32k
Using the following settings.
frame-relay CIR 56000
frame-relay mincir 32000
frame-relay BC 7000
frame-relay BE 24000
frame-relay adaptive becn
You would get the following traffic shaping.
Tc = 125 us or 8 time intervals per second.
BE would permit the host site would be allowed to transmit 31000 bits
in the first interval or a rate equivalent to 248k {remember this is
only for the first interval of a burst not a sustained rate assuming
there are tokens available allowing the frame switch to buffer the
excess data towards the remote end}
sustained rate is 7000 bits per time interval or 56000 bits/sec.
This allows the host site to transmit a sustained rate equal to the
port speed of the remote end and burst to the frame cloud for the first
interval of each second if tokens are available. This is good. If the
host site begins receiving BECN's it cuts the sustained rate back until
it doesn't to a minimum of mincir which is the Carrier committed rate.
This method shapes the output of a high speed host circuit to max
throughput to a slower speed remote end, as long as there is no
congestion notification it will try to send at a sustained rate equal to
the remote end port speed and fallback upon congestion notifications.
Remember FRTS is not just trying to limit data throughput to carrier CIR
but also maximize throughput and intelligently {well somewhat} make use
of congestion notifications to eliminate lost packets and
retransmissions.
Hope this is helpful.
Robert Rech
Senior Network Engineer
Cap Gemini Ernst & Young
Kansas City Service Center
rjrech@cgeykcsc.com
phone (816) 459-4767
fax (816) 459-6767
>>> Jim Brown <Jim.Brown@CaseLogic.com> 08/26/02 09:24AM >>>
After your e-mails I rethought my stance on FRTS. I did a little more
research and I believe my original configuration at the bottom of the
post
is the correct answer from a lab or testing context for a 96Kbps port
and
64Kbs contracted CIR.
map-class frame-relay TestShape
frame-relay cir 64000
frame-relay be 32000
frame-relay bc 8000
I'm basing this on a single new piece of information I turned-up. Check
the
Networkers 2002 CCIE Power Session, in their FRTS example, they
configure
the parameters exactly as I have described below.
I still stand by my original assessment of Cisco's CIR set to the
providers
CIR and Cisco's BE set to the difference between providers CIR and
port
speed.
I'm posting this back to the list to hopefully open up discussion
again.
-----Original Message-----
From: kpalmer [mailto:kip.palmer@verizon.net]
Sent: Sunday, August 25, 2002 8:27 PM
To: 'Jim Brown'
Subject: RE: I need FRTS help or review
Line speed | Access Rate | Port Speed
=======================================
What you bought from the Provider. Per DLCI.
Average Rate | configured CIR (not mincir)
=======================================
When Shaping 128 to 64, it's 64k, with Bc ='s the Average Rate of
remote
64, /8.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
Jim Brown
Sent: Sunday, August 25, 2002 1:04 PM
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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