Re: Riddle me this - QoS Bursting vs Physical Interface

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Content preview: Thanks Karim! Make a small loan, Make a big difference - Kiva.org
   From: Karim Jamali To: Dave Serra Cc: Cisco certification Sent: Fri, December
   3, 2010 10:42:18 AM Subject: Re: Riddle me this - QoS Bursting vs Physical
   Interface Bursting [...]

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Date: Sun, 5 Dec 2010 08:29:58 -0800 (PST)
From: Dave Serra <maybeedave_at_yahoo.com>
Subject: Re: Riddle me this - QoS Bursting vs Physical Interface
  Bursting
To: Karim Jamali <karim.jamali_at_gmail.com>
Cc: Cisco certification <ccielab_at_groupstudy.com>
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Thanks Karim!
 Make a small loan, Make a big difference - Kiva.org
________________________________
From: Karim Jamali <karim.jamali_at_gmail.com>
To: Dave Serra <maybeedave_at_yahoo.com>
Cc: Cisco certification
<ccielab_at_groupstudy.com>
Sent: Fri, December 3, 2010 10:42:18 AM
Subject: Re:
Riddle me this - QoS Bursting vs Physical Interface Bursting

Hi David,

There
is a confusion you are going into..It is true that the interfaces can be
on(send at full rate) or off (no sensing at all)..Tc is an interval that of
time
and Bc is the amount of data that you send within this Tc..For instance
as per
your numbers the Bc 1280 will be sent within a time of Bc divided by
physical
speed of interface and not the cir that is Bc/10Mbps..This will be
an interval
of time smaller than the Tc..Thus for that Tc you will be sending
for that time
you calculated and you will be off for the remaining period
within Tc.

HTH

Karim Jamali

On Dec 3, 2010, at 5:46 PM, Dave Serra
<maybeedave_at_yahoo.com> wrote:

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> Content preview: Ok guys,
forgive this question if it seems too basic but in
> my QoS studies I seem to
find contradiction in how Tc / Bc works for shaping.
> Lets say we have a
10Mbps ethernet link and I have a queue that I will shape
> to 128000 bps and
a burst (Bc) set to 1280 bits which makes Tc = 10ms. So
> in other words,
this ethernet interface will send packets from the shape
> queue at 1280 bits
of traffic for 10ms which to total a speed of 128000 bps.
> Now I also read
that this ethernet interface (actually I read that all
>physical
>
interfaces) can only send at either full line rate or not at all...thus the
>
contraction is (at least in my mind)....if this 10 Mbps ethernet interface
>
were to burst for 10ms (our Tc) we would be sending 100000 bps for every
> Tc
and not 1280 bps. [...]
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> Date: Fri, 3
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> From: Dave Serra <maybeedave_at_yahoo.com>
>
Subject: Riddle me this - QoS Bursting vs Physical Interface Bursting
> To:
Cisco certification <ccielab_at_groupstudy.com>
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> Ok
guys, forgive this question if it seems too basic but in my QoS studies I
>
seem to find contradiction in how Tc / Bc works for shaping. Lets say we have
> a
> 10Mbps ethernet link and I have a queue that I will shape to 128000 bps
and
> a
> burst (Bc) set to 1280 bits which makes Tc = 10ms. So in other
words, this
> ethernet interface will send packets from the shape queue at
1280 bits of
> traffic for 10ms which to total a speed of 128000 bps. Now I
also read that
> this ethernet interface (actually I read that all physical
interfaces) can
> only
> send at either full line rate or not at all...thus
the contraction is
> (at least
> in my mind)....if this 10 Mbps ethernet
interface were to burst for
> 10ms (our
> Tc) we would be sending 100000 bps
for every Tc and not 1280 bps.
> So to put this in the form of a question; How
is it that a shape queue can
> burst
> for a 10ms and not send at full line
rate? Is it simply a matter of
> the
> software shapped queue itself only
bursting this traffic out of its queue
> on to
> the mother board bus and to
the interface where the tx_ring sends the
> traffic at
> full line rate of
100000 bps per Tc ?
>
> I'm hoping one of you can
> untangle the spagetti I
have in my mind
>
> Thanks in advance :)
>
> David Serra
>
>
> Blogs and
organic groups at http://www.ccie.net
>
>
Received on Sun Dec 05 2010 - 08:29:58 ART