RE: QOS Bc Be and Tc

I want to thank my GS friends Carlos G Mendioroz and Narbik for pointing out that given the actual numbers I put in my explanation below - the interface will not have to send for an entire 125 ms Tc. I should not have put the numbers in actually as I wanted to stay abstract and not get into the math of it.

I find so many candidates can do the shaping math no problem - but they do not really understand what Bc really is and why It is important.

Well - thanks for reading and I hope I did more good than harm.

:-)

-----Original Message-----
From: Anthony Sequeira
Sent: Wednesday, August 18, 2010 3:06 PM
To: masroor ali; Cisco certification
Subject: RE: QOS Bc Be and Tc

Let us say that a Cisco router WAN interface is capable of sending at T1 speed (1.54 Mbps). This is called the Access Rate (AR).

Now - you make a deal with a Service Provider to send at 512 Kbps. This is called the Committed Information Rate (CIR).

You have got a big problem. There is no dial you can turn like on a kitchen faucet in order to slow the rate at which your interface sends traffic. The interface can ONLY operate at 1.54 Mbps.

So the router does a neat trick. It divides a second into timing intervals (portions of a second or Tc). The default division of the second is to slice it up into 8 timing intervals of 125 milliseconds each. It will send data in one of these timing intervals, and then not send in the next, then send, then not send. By doing this it can AVERAGE the 512K over the course of a second.

The amount of data that you send in one of these timing intervals is the committed burst or Bc.

If you are a really lucky customer, your provider might let you burst above the 512K. To do this - you send some data in the previously unused timing intervals (Tc). This amount you send is called the committed burst (Be).

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of masroor ali
Sent: Wednesday, August 18, 2010 2:52 PM
To: Cisco certification
Subject: QOS Bc Be and Tc

hi,

Can anyone explain in easy wordings that what is Bc Be and Tc

-- 
Regards,
Masroor Ali
Blogs and organic groups at http://www.ccie.net