From: Athaide, Dwayne (DAthaide@epco.com)
Date: Fri May 30 2008 - 20:21:43 ART
I attended Narbik's bootcamp this May and after his excellent lecture on QOS
brought this very example in the DOC CD to his attention. We got the exact
same result as you did and concluded that to get a throughput of 512K
(provided bc=be) we need to set the peak of 256K.
In any case another student in my class found a better explanation which I
have pasted below. So basically, If I was asked a question like u asked below
which is to set the bandwidth to 300k but if enough bandwidth is available
obtain a throughput upto a peak 512K. I would do the following.
Policy qos
Class test
Bandwidth 300
Shape peak 256
http://www.ciscopress.com/articles/article.asp?p=352991&seqNum=9
Chapter 9
Consider the following CB-Shaping example, where you are shaping one class-map
to average and another class-map to peak:
Router(config)#class-map AVERAGECLASS
Router(config-cmap)#match protocol telnet
Router(config-cmap)#exit
Router(config)#class-map PEAKCLASS
Router(config-cmap)#match protocol http
Router(config-cmap)#exit
Router(config)#policy-map AVERAGEPOLICY
Router(config-pmap)#class AVERAGECLASS
Router(config-pmap-c)#shape average 64000
Router(config-pmap-c)#exit
Router(config-pmap)#exit
Router(config)#policy-map PEAKPOLICY
Router(config-pmap)#class PEAKCLASS
Router(config-pmap-c)#shape peak 64000
In this example, the AVERAGEPOLICY policy-map is shaping Telnet traffic to
average, meaning that Telnet traffic is shaped to the CIR of 64 kbps. However,
that is not the case for the PEAKPOLICY policy-map.
The PEAKPOLICY policy-map is shaping traffic to a peak rate of CIR * [1 +
(Be/Bc)]. Because you let the IOS calculate the Bc and Be values, they are
equal, which means that you are shaping to a rate of 64000 * (1 + 1) = 128
kbps.
From: raul raul [mailto:juvenn@hotmail.com]
Sent: Friday, May 30, 2008 8:40 AM
To: Athaide, Dwayne; ccielab@groupstudy.com
Subject: RE: shape peak
Hi
are u sure cisco will make mistake in thier doc cd ?
Anybody pls help to clarify and explain
Thanks
________________________________
> From: DAthaide@epco.com
> To: juvenn@hotmail.com; ccielab@groupstudy.com
> Date: Fri, 30 May 2008 08:17:25 -0500
> Subject: RE: shape peak
>
> I think the Cisco example you mentioned below is incorrect in the DOC CD.
If
> you want a throughput of 512K then you will need to do a shape peak of 256K
> (if bc=be).
>
>
>
>
>
> The following example uses peak rate shaping to ensure a bandwidth of 300
> kbps
>
> but allow throughput up to 512 kbps if enough bandwidth is available on the
>
> interface:
>
> bandwidth 300
>
>
>
> shape peak 512000
>
>
>
>
>
>
>
> why is shape peak 512000 on cisco article ?
>
> if i shape peak then i will get 1024000; is this correct ? or other way
round
>
> ? pls explain ? Traffic Shaping Target/Average Byte Sustai n
>
> Excess
>
> Interval Increment Rate Limit bits/int bits/int
>
> (ms) (bytes) 1024000/512000 3200 12800 12800
>
> 25 3200
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
raul
> raul
> Sent: Thursday, May 29, 2008 10:49 PM
> To: ccielab@groupstudy.com
> Subject: shape peak
>
>
>
> Hi ;
>
>
>
> need help
>
>
>
>
>
> Usage Guidelines
>
> Traffic shaping limits the rate of transmission of data. In addition to
using
>
> a specifically configured transmission rate, you can use Generic Traffic
>
> Shaping (GTS) to specify a derived transmission rate based on the level of
>
> congestion.
>
> You can specify two types of traffic shaping; average rate shapi ng and
peak
>
> rate shaping. Average rate shaping limits the transmission rate to the CIR.
>
> Using the CIR ensures that the average amount of traffic being sent
conforms
>
> to the rate expected by the network.
>
> Peak rate shaping configures the router to send more traffic than the CIR.
To
>
> determine the peak rate, the router uses the following formula:
>
> peak rate = CIR(1 + Be / Bc)
>
> where:
>
> Be is the Excess Burst size.
>
> Bc is the Committed Burst size.
>
> Peak rate shaping allows the router to burst higher than average rate
> shaping.
>
> However, using peak rate shaping, the traffic sent above the CIR (the
delta)
>
> could be dropped if the network becomes congested.
>
> If your network has additional bandwidth available (over the provisioned
CIR)
>
> and the applica tion or class can tolerate occasional packet loss, that
extra
>
> bandwidth can be exploited through the use of peak rate shaping. However,
>
> there may be occasional packet drops when network congestion occurs. If the
>
> traffic being sent to the network must strictly conform to the configured
>
> network provisioned CIR, then you should use average traffic shaping.
>
> Examples
>
> The following example sets the uses average rate shaping to ensure a
> bandwidth
>
> of 256 kbps:
>
> shape average 256000
>
>
>
>
>
> The following example uses peak rate shaping to ensure a bandwidth of 300
> kbps
>
> but allow throughput up to 512 kbps if enough bandwidth is available on the
>
> interface:
>
> bandwidth 300
>
>
>
> shape peak 512000
>
>
& gt;
>
>
>
>
> why is shape peak 512000 on cisco article ?
>
> if i shape peak then i will get 1024000; is this correct ? or other way
round
>
> ? pls explain ? Traffic Shaping Target/Average Byte Sustain
>
> Excess
>
> Interval Increment Rate Limit bits/int bits/int
>
> (ms) (bytes) 1024000/512000 3200 12800 12800
>
> 25 3200
>
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