From: Kenny (frenzeus@streamyx.com)
Date: Fri Apr 21 2006 - 15:50:25 GMT-3
Hi Scott,
I was searching out for this question of Lab10 as well & happen to bump into
ur mail. I'm actually more concern on specifically when does shaping &
fragmentation actually take place.
I read through the Ciscopress QoS 2nd edition book and it seems that shaping
actually occurs before fragmentation. Say there is now congestion on the
software queues, and a packet arrives (which is larger than 320bytes) and
exceeds the configured Bc, so it gets shaped inside the shaping queue.
According to the book, it seems that only when the shaping scheduler decides
to de-queue the packet only then it is checked if the packet actually is
larger than 320bytes, and if so it is fragmented. So it seems to me that a
single packet is actually taking more than 1 interval to be transmitted when
the packet is in the shaping queue since the actual fragmentation of the
packet only occurs after it is being shaped.
Appreciate if u could clarify if I'm looking at this in the wrong direction.
Thanks a lot.
Cheers,
K
----- Original Message -----
From: "Scott Smith" <hioctane@gmail.com>
To: "Moin, Imran" <imoin@virtela.net>
Cc: "Group Study (E-mail)" <ccielab@groupstudy.com>
Sent: Sunday, March 12, 2006 1:47 PM
Subject: Re: IE Lab10 - FRTS
> Tc = 10ms (smallest possible)
> Bc = CIR * Tc
> Bc = 256000 * .01 (10/1000 =.01)
> Bc = 2560
> fragment = 2560 / 8
> fragment = 320 (fragment is in bytes so 2560 bits in bytes is 320)
>
> Changing the fragment to 320 ensures "that a single packet cannot take
> more than one interval to be transmited".
>
> -Scott
>
> On 3/11/06, Moin, Imran <imoin@virtela.net> wrote:
>> Hello Folks,
>>
>> Can someone please help me understand how the values of Bc and
>> frame-relay
>> fragment were derived in Question number 8.1 (FRTS).
>>
>> Thanks,
>> Imran.
>>
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