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RE: QoS - Enabling Traffic Shaping [7:70877] posted 06/18/2003
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Jonathan,

	First let's make sure we're on the same page with definitions.
For traffic-shaping (both GTS and FRTS), the terms are as follows:

AR  = Access Rate (physical clock or rate-limit at local loop)
CIR = Average per second
Bc  = Bits per interval committed
Be  = Bits per interval excess
Tc  = Interval in ms

	The following formula should be used to calculate Bc:

Bc = CIR * Tc/1000

	The following formula should be used to calculate Be:

Be = (AR - CIR) * Tc/1000


	In this example, our access-rate is 64000bps.  We are trying to
average 15% of our access rate for telnet traffic.  Average per second
is CIR.

CIR = 64000 bps X .15 = 9600 bps

	Let's assume for this example that our Tc is 1/8 second, or 125
ms.  Our committed burst size would then be as follows:

Bc = CIR * Tc/1000
Bc = 9600 * 125/1000
Bc = 9600 * .125
Bc = 1200

	Now let's double check our calculation.

We have 125 ms per interval.  There are 1000 ms per second.

1 interval | 1000 ms
--------------------- = 8 intervals per second
  125 ms   | 1 second

If we are sending 1200 bits per interval 8 times per second:

1200 bits  | 8 intervals
------------------------ = 1200 * 8 = 9600bps
1 interval | 1 second


As a side note, if you want no excess burst, you want the Be value to be
zero, not the same as the Bc value.  The syntax should then read as
follows:

traffic-shape group 101 9600 1200 0



HTH

Brian McGahan, CCIE #8593
Director of Design and Implementation
brian@xxxxxxxxxxxxxxx

CyscoExpert Corporation
Internetwork Consulting & Training
Toll Free: 866.CyscoXP
Fax: 847.674.2625


> -----Original Message-----
> From: Jonathan V Hays [mailto:jhays@xxxxxxxx]
> Sent: Wednesday, June 18, 2003 11:39 AM
> To: 'John Smith'; cisco@xxxxxxxxxxxxxx; ccielab@xxxxxxxxxxxxxx
> Cc: CCNP_Study_Group@xxxxxxxxxxxxxxx; CCSP-Security@xxxxxxxxxxxxxxx;
> info@xxxxxxxxxxxxxxx; CertificationTalk@xxxxxxxxxxxx
> Subject: RE: QoS - Enabling Traffic Shaping
> 
> John,
> 
> I assume the '25' after each percentage sign in your original post
below
> is a typo (e.g., "15%25 of bandwidth"). Given that assumption, you
want
> to assign traffic to three categories, with 15%, 50%, and 35% of the
64
> kbps bandwidth.
> 
> 64000 x .15 =  9600 bps
> 64000 x .50 = 32000 bps
> 64000 x .35 = 22400 bps
> 
> > burst size should 1/8 of the bit rate cfg'd, no excess burst
> 
> 1/8 = .125
> 
>  9600 x .125 = 1200 bps
> 32000 x .125 = 4000 bps
> 22400 x .125 = 2800 bps
> 
> However, I question the burst size given in your solution. The
> definition from the Doc CD states that the  burst-size is the
"Sustained
> number of bits that can be sent per INTERVAL. On Frame Relay
interfaces,
> this is the Committed Burst size contracted with your service
provider.
> "
> 
> See
>
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
> fqos_r/qrfcmd11.htm#1019905
> 
> If the interval is 1/8 second (and it may not be) I would think the
> correct answer would divide each of 1200, 4000, and 2800 by 8, to get
> bits per interval.
> 
> HTH,
> 
> Jonathan
> 
> > -----Original Message-----
> > From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On
> > Behalf Of John Smith
> > Sent: Wednesday, June 18, 2003 10:21 AM
> > To: cisco@xxxxxxxxxxxxxx; ccielab@xxxxxxxxxxxxxx
> > Cc: CCNP_Study_Group@xxxxxxxxxxxxxxx;
> > CCSP-Security@xxxxxxxxxxxxxxx; info@xxxxxxxxxxxxxxx;
> > CertificationTalk@xxxxxxxxxxxx
> > Subject: QoS - Enabling Traffic Shaping
> >
> >
> > Somehow I have forgotten how to do math... Can anyone explain
> > to me or point to a doc on figuring out the percentage for
> > the below lab.
> >
> > Enable traffic shaping on int serial 0/0 as follows:
> >
> > Shape Telnet and ICMP traffic to 15%25 of bandwidth
> > Shape FTP traffic to 50%25 of bw
> > Shape all remianing traffic to 35%25 of bw.
> >
> > Remember the total link bw is 64 kbps on this interface. The
> > burst size should 1/8 of the bit rate cfg'd, no excess burst
> > should be allowed.
> >
> > The answer from the lab help are, below can anyone tell me
> > how the number 9600, 32000 and 22400 were arrived at? I can
> > figure out the 1/8th part 1200, 4000 and 2800, but somehow
> > can't remember how to get the original percentage..
> >
> > traffic-shape group 101 9600 1200 1200
> > traffic-shape group 102 32000 4000 4000
> > traffic-shape group 103 22400 2800 2800
> >
> > Thanks.
> >
> >
> >
> > ---------------------------------
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> >
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