From: Steve (steve.ccie@googlemail.com)
Date: Tue Aug 14 2007 - 05:54:49 ART
Hi,
OK - I think I have it now (underline THINK).....
Tc is derived from the CIR (or max rate in this case) and Bc values -
you don't actually calculate that at all.
So, if you want to shift 3584 bytes per interval (read Tc) then you
need to convert that to bits (Bc per Tc is bits) .... Bc = 3584 * 8 =
28672 bits
Now, with R1 having max rate of 896kbps, apply that rate and the Bc
to formula Tc = Bc / CIR...... Tc = 28672 / 896000 = 0.032 seconds or
32msec.
Now, apply the same process to the other link - R2 - R3 and it
matches the answer from the book as well.
Hopefully I have that all correct - if so, I will smile for the first
time in several days of trying to get this sorted in my head as well.
HTH
Cheers,
Steve
On 14 Aug 2007, at 09:22, slevin kremera wrote:
> Hi Steve/joseph
> Everything seems ok except for Tc.how did they get that... and what
> significance does the last part of the question have to the
> calculation of Tc
>
>
> On 8/14/07, Steve <steve.ccie@googlemail.com> wrote:
> Hi,
>
> I am a little confused - where does the /1000 come into this equation?
> I understood Bc = CIR * Tc ...?
>
> I have looked at that question as well now and am scratching my
> head.....hope someone can clarify as
> I have been studying the frame shaping lately and can admit that it
> is taking some time to sink into my thick skull.
>
> Cheers,
> Steve
>
>
> On 14 Aug 2007, at 02:43, Joseph Brunner wrote:
>
> > Yo Adrian,
> >
> > The formula to calculate bc is
> >
> > BC = CIR * tc/1000
> >
> > They tell you the tc in these types of questions, so that variable
> > shouldn't
> > be a mystery...
> >
> > That last bit of the question... FRF.12, or fragmentation... they
> > are just
> > matching fragment size to the amount of data you can send in one
> > tc. Just
> > remember the fragment size is entered in bytes (frame-relay fragment
> > command), where the tc is in bits and is not directly set, its
> > actually set
> > by setting the bc!
> >
> > Joe
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> > Behalf Of
> > slevin kremera
> > Sent: Monday, August 13, 2007 9:03 PM
> > To: Cisco certification
> > Subject: iewb v3 lab4 task 8.1 frame-relay QOS
> >
> > Hi Group
> >
> > The CIR part makes sense.But how did he get Bc?? and how is the
> > last bit
> > where it says R1 and R3 should be able to trasmit a maximum of 3584
> > byres
> > shaping interval and R2 and R3 shud be able to transmit a maximum
> > of 2560
> > bytes.
> >
> > Is it that the last bit was used to calculate Bc ? if so how??
> >
> > thks
> >
> >
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