From: Bob Chahal (bob.chahal@xxxxxxxxxxxx)
Date: Wed Jun 06 2001 - 15:59:50 GMT-3
I've been looking for an explanation like that. Thanks.
Bob
----- Original Message -----
From: "David Anderson" <dma@cisco.com>
To: "Ryan LaTorre" <cisco@crl.fdns.net>
Cc: "Groupstudy" <ccielab@groupstudy.com>
Sent: Wednesday, June 06, 2001 7:26 PM
Subject: Re: custom queue: determining byte-count?
> Here is a good explanation of determining the byte count in custom
queuing:
> Determining the Byte Count
>
> To ensure that the configured bandwidth allocation is as close as possible
> to the required bandwidth allocation you must determine the byte count
> based on each
> individual protocol's frame size. Without doing this, your percentages may
> not match what you configure.
>
> For example, suppose one protocol has 500 byte frames, another has 300
byte
> frames, and a third has 100 byte frames If you want to split the bandwidth
> evenly
> across all three protocols, you might chose to specify byte counts of 200,
> 200, and 200 for each queue. However, that will not result in 33/33/33
> ratio. That is
> because when the router serviced the first queue it would send a single
500
> byte frame, when it serviced the second queue it would send a 300 byte
> frame, and when
> it serviced the third queue it would send two 100 byte frames, giving you
> an effective ratio of 50/30/20. Had you instead specified 1000, 1000,
1000,
> the router
> would send 2 500 byte frames, 5 200 byte frames, and 10 100 byte frames
> with a bandwidth ratio of exactly 33/33/33.
>
> However, the delay to send 1000 bytes might be too large. Another
> alternative is to specify 500, 600, 500 which will result in a ratio of
> 31/38/31, which may be
> acceptable.
>
> Fortunately, you do not have to use trial and error to determine the
> correct byte counts. Instead, simply follow these steps:
>
> 1) Produce a ratio of all frame sizes, starting with the largest as 1. For
> example, assume the frame sizes of protocol A were 1086 bytes, protocol B
> were 291 bytes
> and protocol C were 831 bytes. The ratios would be:
>
> 1086/1086, 1086/291, 1086/831
>
> 2) Now multiply the results by the percentages of bandwidth you want each
> protocol to have. In this example we will allocate the following
> percentages, 20% for A,
> 60% for B, and 20% for C. This will give us:
>
> 1086/1086(0.2), 1086/291(0.6), 1086/831(0.2)
>
> or
>
> .2, 2.239, 0.261
>
> 3) Again, normalize the ratio by dividing each value by the smallest
value,
> that is
>
> .2/.2, 2.239/.2, .261/.2 which equals 1, 11.2, 1.3
>
> This is the ratio of the number of frames that must be sent such that the
> percentage of bandwidth that each protocol uses is approximately in the
> ratio of
> 20%,60%,20%.
>
> 1.Note that any fraction in any of the ratio values means that an
> additional frame will be sent. In the example above, the number of frames
> sent would be 1
> (1086 byte frame), 12 (291 byte frames) and 2 (831 byte frames) or
> 1086, 3492, and 1662 bytes respectively from each queue. These are the
byte
> counts
> you would specify in your custom queuing configuration.
>
> To determine this bandwidth distribution this represents, first determine
> the total amount of bytes sent after all three queues are serviced:
>
> 1 x 1086 + 12 x 291 + 2 X 831 = 1086 + 3492 + 1662 = 6240
>
> Then determine the percentage of the 6240 bytes that was sent from each
queue:
>
> 1086/6240, 3492/6240, 1662/6240 = 17.4%, 56%, 26.6%
>
> As you can see, this is close to the desired ratio of 20/60/20. The
> resulting bandwidth allocation can be tailored further by multiplying the
> original ratio of 1:11.2:1.3
> by an integer, and trying go get as close to three integer values as
> possible. For example, if we multiply the ratio by 2, we get 2:22.4:2.6.
We
> would now send 2
> (1086 byte frames), 23 (291 byte frames) and 3 (831 byte frames) or
> 2172/6693/2493 for a total of 11358 bytes. The resulting ration is
> 19%/59%/22% which is
> much closer to our desired ratio that we achieved above.
>
> Do not forget that using a very large byte count may cause other problems.
>
> At 02:12 PM 6/6/2001 -0400, Ryan LaTorre wrote:
> > There is a section in the Cisco Press "IP Quality of Service" book on
> > this, but if you don't have the book, I also found some discussion of
> > this at:
> >
> >
> >http://127.0.0.1:8080/cc/td/doc/product/software/ios120/12cgcr/qos_c/qcp
> >art2/qcconman.htm#xtocid57019
> >
> > Not having a lot of real-world experience with extensive QoS, I found
> > the Ciscopress book to be pretty good. It is very new, and covers the
> > modular CLI as well. Check it out...
> >
> > From the perspective of the lab, I would hope they're not expecting
> > candidates to memorize "average" byte counts for different protocols.
> > Many protocols vary greatly anyhow - IP can be 64 bytes average is
> >voice
> > is the only traffic type being used (for example) but if FTP is
> > extensively in use, maybe it's upwards of 1500 bytes...
> >
> > Ryan
> >
> > > ----- Original Message -----
> > > From: "Daniel C. Young" <danyoung99@mediaone.net>
> > > To: <ccielab@groupstudy.com>
> > > Sent: Wednesday, June 06, 2001 3:15 AM
> > > Subject: custom queue: determining byte-count?
> > >
> > >
> > > > Group,
> > > >
> > > > How do you determine which byte-count to use? I have read in several
> > > places
> > > > on Cisco's web site that it all depends on the byte count of the
> > > protocol.
> > > > But does anyone know the byte counts of specific protocols for, say
> > > SNA?
> > > >
> > > > Is there a resource that lists the proper byte counts for all the
> > > protocols?
> > > >
> > > > Many thanks,
> > > >
> > > > Daniel C. Young
> > > > Sr. Network Engineer
> > > > CCNP (ATM, Security & Voice Specialist),
> > > > CCDP, CCSE, MCSE+I
> > > >
> > > > SBC Internet Data Center
> > > > (949) 221-1928 Work
> > > > (714) 350-8945 Cell
> > > > young@pobox.com
> > > > **Please read:http://www.groupstudy.com/list/posting.html
> >**Please read:http://www.groupstudy.com/list/posting.html
> David Anderson
> Network Design Engineer
> Enterprise Solutions Architecture & Design
> (408) 853-5515
> dma@cisco.com
> | |
> ..:|||||||:...:|||||||:..
> C I S C O S Y S T E M S
> **Please read:http://www.groupstudy.com/list/posting.html
**Please read:http://www.groupstudy.com/list/posting.html
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