From: Roberto Fernandez (rofernandez@us.telefonica.com)
Date: Thu Jun 08 2006 - 18:25:04 ART
Godswill,
The thing its not open to interpretations. Bc means Burst Committed, and
it means how much you can send on a Tc. It is really a Burst measure. It
makes the difference if it is larger or shorter. Shows how fast you can
empty your bucket.
If you go to the question you will see there is not doubt about the
answer.
Best Regards,
Roberto
-----Original Message-----
From: Godswill Oletu [mailto:oletu@inbox.lv]
Sent: Thursday, June 08, 2006 8:08 AM
To: Navin MS; Roberto Fernandez; Brian McGahan; Leigh Harrison; Andi
Bennett
Cc: ccielab@groupstudy.com
Subject: Re: FRTS Lab 1 - 7.2 question.
Navin,
We might be saying the same but differently; the thing is I really do
not
consider it a burst, if you allow me to burst upto Bc within each Tc but
at
the end of the day, I cannot send more than my CIR. After all is said
and
done, I am still limited to my CIR.
And, I am kind of having a weird feeling that, if a question states that
the
CIR is eg 128kbps and the question further states that allow for some
burst
and one configure only CIR and Bc; he/she have not sufficiently fulfill
the
tasks set forth in the question.
Configuring CIR and Bc only fulfill the aspect of the task that is
dealing
with CIR and by including a Bc; you are telling the router that, you
want to
be in charge; you want to be the one who decides the rate at which you
want
to send on each Tc timeslot and by that you are also dictating to the
router
the value of the Tc to be used. And the router will only accept you Bc
value
if it makes sense. If on the other hand, you did not configure Bc, the
router will configure one for you, but all these have not fulfill the
aspect
of the task that states '....allow for some burst'.
R3640-R1(config-pmap-c)#shape average 128000 ?
<256-154400000> bits per interval, sustained. Needs to be multiple of
128.
Recommend not to configure it, the algorithm will
find
out
the best value
<cr>
R3640-R1(config-pmap-c)#shape average 128000
*note, what the router is saying about Bc'...recommended not to
configure
it, the algorithm will find out the best value'
>
> 1) Send traffic at a constant rate of CIR (in which case Bc of 4000 is
unused). Though you were
> allowed to burst, you didn't :)
>
Can you explain this further? Is it possible not to use Bc? How can one
send
at constant rate of CIR without using Bc? My experience had been, even
if
you did not specify Bc, the router will calculate and impose one on you.
The only theorical time, I think one can send at constant rate of CIR
will
be when Tc= 1 sec, but the maximum recommended Tc is 10ms, so whether,
we
like it or not, we will be forced to divide our CIR into junks of Bc and
are
allowed to burst from 0 to that Bc value within each Tc.
Look at my attempt at my failed attempt at forcing my router to accept a
very high Tc of 2ms; which is a long shot from the theoritical Tc vlaue
of
1sec assumed above.
R3640-R1(config-pmap-c)#shape average 128000 256
less than 1000 bits in an interval doesn't make sense
R3640-R1(config-pmap-c)#
The router took on some little attitude there, telling me that what I am
trying to accomplish 'doen't make sense'.
>
> 3) Send a burst of (Bc + Be) bits per Time interval (if Be is
configured,
in which case you are
> using Bc of 4000 and Be of 2000 say). When you do this, you are
effectively sending more than CIR.
> That is, your Tx rate = (Bc+Be)/Tc which is greater than (Bc/Tc).
>
This not guarantee at all time, in essence your effective/constant Tx
rate
will not be (Bc+Be)/Tc; In shaping with Bc and Be configured, you can
only
send above Bc per timing interval when you have accumulated credit to do
so
from the previous timing interval.
Read the section 'Traffic Sahping and Rate of Transfer here:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fqos_c/fqcprt4/qcfpolsh.htm
In policing, configuring Bc & Be and the process of determining how the
Be
get used, involve a complex set of algorithms, that will include
borrowing
tokens, compounded debts, etc.
Read the section 'Rate Limits' and other sections below it:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fqos_c/fqcprt4/qcfpolsh.htm.
Excuse, my rather lengthy email and also remember that, there are many
QoS
gurus on this list and I am not one of them.
HTH
Godswill Oletu
HTH
Godswill Oletu
----- Original Message -----
From: "Navin MS" <navin_ms07@yahoo.com>
To: "Godswill Oletu" <oletu@inbox.lv>; "Roberto Fernandez"
<rofernandez@us.telefonica.com>; "Brian McGahan"
<bmcgahan@internetworkexpert.com>; "Leigh Harrison"
<ccileigh@gmail.com>;
"Andi Bennett" <bigandibennett@yahoo.com>
Cc: <ccielab@groupstudy.com>
Sent: Thursday, June 08, 2006 12:16 AM
Subject: Re: FRTS Lab 1 - 7.2 question.
> Yes, When it comes to plain English.. a burst is thought of something
in
excess that a router is
> sending into the FR cloud. BUT from a frame-relay perspective, it
simply
says how many bits in
> burst can be sent in one Time interval. Bc just gives us bursting
capability which is very much
> required given the sporadic nature of real-time traffic. I have an
easy
alternate way of
> understanding this. One can look at it this way.
>
> For a customer there are 4 options...
>
> 1) Send traffic at a constant rate of CIR (in which case Bc of 4000 is
unused). Though you were
> allowed to burst, you didn't :)
>
> 2) Send a burst of Bc bits per Time interval (in which case you are
using
Bc of 4000 bits). When
> you do this, you are effectively sending CIR bps (Bc/Tc) as agreed.
>
> 3) Send a burst of (Bc + Be) bits per Time interval (if Be is
configured,
in which case you are
> using Bc of 4000 and Be of 2000 say). When you do this, you are
effectively sending more than CIR.
> That is, your Tx rate = (Bc+Be)/Tc which is greater than (Bc/Tc).
>
> 4) Send traffic which is constant for some part of the Time interval
and
random burst for some
> other part of Time interval. Eg: For a period of say, Tc/2 you sent
3000
bits at a constant
> bit-rate and another Tc/2 you send a random burst of 1000 bits.
Together,
you sent 4000 bits in
> that interval. THAT CONFORMS TO CIR. Now, if you send anything more
than
4000 bits, you will be
> using the extended Burst capability (Be).
>
> Similar reasoning goes for policing too.
>
> Just my 2 cents.
> Naveen.
>
>
>
> --- Godswill Oletu <oletu@inbox.lv> wrote:
>
> > Roberto,
> >
> > Though, I have not checked the question to see if it is shaping or
policing,
> > but if we assume that it is policing as you have just said, I am
lost at
> > how:
> >
> > Police cir 128000 bc 4000
> >
> > Will result in a burst, as the original poster indicated. The
command
above
> > is just telling the router that, in order not to create a scheduling
> > concern, please kindly send 4000 bytes per burst or timing interval
(Tc).
> >
> > Bc is committed burst, you have paid for 128Kbps and you are telling
the
> > router to allow you to burst your traffic from 0 to 4000 per timing
interval
> > (Tc), and this commitment is based on your CIR. The concept of burst
as
we
> > understand it in everyday English only start coming into play with
Be or
> > excess burst.
> >
> > Also, if you look at the computation you just did; you are equating
CIR
to
> > be the same the same value as Bc, but using different metrics, which
might
> > not be the correct thing to do.
> >
> > The CIR given was 128kbps, convert this to bytes will be be 128000 /
8 =
> > 16000 bytes and you divided that by 4 to get 1/4Bc (4000 bytes) that
was
> > asked for.
> >
> > Let assume that a full Bc was asked for instead of 1/4Bc, you see
that
your
> > computation will make Bc = 16000 bytes and this is the same amount
of
> > traffic our CIR is allowing us to transmit per second. In a one
second
> > traffic snapshot, the difference between 128kbps and 16000 bytes is
the
same
> > as the difference between $1 and 100 cents.
> >
> > As you can see, that might not be the correct formula to computer Bc
either
> > in policing or in shaping.
> >
> > HTH
> > Godswill Oletu
> >
> >
> > ----- Original Message -----
> > From: "Roberto Fernandez" <rofernandez@us.telefonica.com>
> > To: "Brian McGahan" <bmcgahan@internetworkexpert.com>; "Godswill
Oletu"
> > <oletu@inbox.lv>; "Leigh Harrison" <ccileigh@gmail.com>; "Andi
Bennett"
> > <bigandibennett@yahoo.com>
> > Cc: <ccielab@groupstudy.com>
> > Sent: Wednesday, June 07, 2006 2:21 PM
> > Subject: RE: FRTS Lab 1 - 7.2 question.
> >
> >
> > Friends,
> >
> > Well... checking into 7.2 question of Version 3 WB, it is not a
question
> > about FRTS it is about policing.
> >
> > With FRTS Bc is bits, but with policing is Bytes, thus 128 kbits/4 =
32
> > kbits => 4K Bytes
> >
> > The answer says
> >
> > Police cir 128000 bc 4000
> >
> >
> >
> > Best Regards,
> > Roberto
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> > Brian McGahan
> > Sent: Tuesday, June 06, 2006 9:45 AM
> > To: Godswill Oletu; Leigh Harrison; Andi Bennett
> > Cc: ccielab@groupstudy.com
> > Subject: RE: FRTS Lab 1 - 7.2 question.
> >
> > > I think it has to do the value of the default 'Tc' (the Tc value
used
> > when
> > > none is supplied) which is 125ms.
> >
> > In this case yes, but not always. The default Tc is a function
> > of the CIR. The higher the CIR the lower the maximum (and default)
Tc.
> > Change the "frame-relay cir" value in a map-class with no other
values
> > configured and look at the "show traffic-shape" output. As the CIR
goes
> > up you will see the Tc go down.
> >
> >
> > HTH,
> >
> > Brian McGahan, CCIE #8593
> > bmcgahan@internetworkexpert.com
> >
> > Internetwork Expert, Inc.
> > http://www.InternetworkExpert.com
> > Toll Free: 877-224-8987 x 705
> > Outside US: 775-826-4344 x 705
> > 24/7 Support: http://forum.internetworkexpert.com
> > Live Chat: http://www.internetworkexpert.com/chat/
> >
> >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
Behalf
> > Of
> > > Godswill Oletu
> > > Sent: Tuesday, June 06, 2006 7:23 AM
> > > To: Leigh Harrison; Andi Bennett
> > > Cc: ccielab@groupstudy.com
> > > Subject: Re: FRTS Lab 1 - 7.2 question.
> > >
> > > LH,
> > >
> > > Maybe, you are talking about 'fragments' which are in bytes,
> > otherwise,
> > > 'CIR' are in bits/second; 'Bc' in Bits and 'Be' in Bits.
> > >
> > > I think it has to do the value of the default 'Tc' (the Tc value
used
> > when
> > > none is supplied) which is 125ms.
> > >
> > > Be=(AR- CIR) * Tc/1000
> > > =(128000 * 125/1000
> > > =16000
> > >
> > > 1/4 Be = Be / 4 = 16000/ 4
> > > = 4000
> > >
> > > My only problem is that, the orignal posted mentioned 'Bc' instead
of
> > > 'Be'.
> > > I do not see how 'Bc' will result in a Burst, except I am missing
> > > something
> > > here or in the question. 'Bc' simply tell us how much need to be
> > > transmitted
> > > per timing interval to conform to our 'CIR'; which is in our case
> > every
> > > 125ms and to conform to our 'CIR' of 128K, that value is 16000.
'Be'
> > tell
> > > us
> > > that, after fulfilling our allocated quota and we have room, how
much
> > > above
> > > CIR should we Burst?
> > >
> > > Since, the Access Rate (AR) was not given in the task, it is safe
to
> > > assume
> > > that 'AR' is equal to 'CIR', making both 'Bc' & 'Be' to be equal
and
> > 1/4
> > > of
> > > Be will be 4000.
> > >
> > > Please, set me straight if I am missing something here.
> > >
> > > Thanks.
> > > Godswill Oletu
> > >
> > >
> > > ----- Original Message -----
> > > From: "Leigh Harrison" <ccileigh@gmail.com>
> > > To: "Andi Bennett" <bigandibennett@yahoo.com>
> > > Cc: <ccielab@groupstudy.com>
> > > Sent: Tuesday, June 06, 2006 6:39 AM
> > > Subject: Re: FRTS Lab 1 - 7.2 question.
> > >
> > >
> > > > Hey there Andi,
> > > >
> > > > CIR is in bits, Bc is in bytes
> > > >
> > > > 128,000 / 4 = 32,000 _bits_ per interval
> > > >
> > > > 32,000 / 8 = 4,000 _bytes_ per interval
> > > >
> > > > Hope that helps a bit,
> > > >
> > > > LH
> > > >
> > > > Andi Bennett wrote:
> > > > > Dear group.
> > > > > Being a bit crap at FRTS can somebody explain the answer to
the
> > Lab
> > > 1
> > > 7.2 question.
> > > > >
> > > > > 128K CIR and allow for 1/4th for burst.
> > > > >
> > > > > How does this come up with bc = 4000 ?
> > > > >
> > > > > Am I missing something here?
> > > > > Cheers
> > > > > A.
> > > > >
> > > > >
> > > > >
> > > > > Send instant messages to your online friends
> > > http://uk.messenger.yahoo.com
> > > > >
> > > > >
> > >
> >
This archive was generated by hypermail 2.1.4 : Sat Jul 01 2006 - 07:57:32 ART