3 Replies Latest reply: Apr 26, 2014 9:57 AM by Bahaa RSS

    Calculation for Tc

    Augustine

      hey gurus am preparing for my QoS exam but still have problems with Bc,Be,Tc,Te in shaping and policing. i need some from u guys because i read it over but still face some problems.

       

      For example given a CIR = 64000 and Bc = 8000 what is the Tc and how do we find it? Is the calcution for Tc in policing similar to that for Tc for shaping

         
        • 1. Re: Calculation for Tc
          Keith Barker - CCIE RS/Security, CISSP

          hey gurus am preparing for my QoS exam but still have problems with Bc,Be,Tc,Te in shaping and policing. i need some from u guys because i read it over but still face some problems.

           

          For example given a CIR = 64000 and Bc = 8000 what is the Tc and how do we find it? Is the calcution for Tc in policing similar to that for Tc for shaping

           

           

           

          Tc = Bc/CIR (in seconds) is the formula.

           

          The router internally calculates the value of Tc based on the configured CIR and Bc values.


          If Bc/CIR is more than or equal to 125 ms, it uses an internal Tc value if the router determines that traffic flow will be more stable with a smaller interval.
          You can use the show traffic-shape command to determine whether your router is using an internal value for Tc or the value that you configured.

           

          In your example with CIR of 64K and Bc of 8000K, (8,000/64,000) = 0.125 or 125ms.    If we wanted a Tc of 100ms, we would simply configure the Bc to be 6400.  Then  using the formula Tc=Bc/CIR it would be 6,400/64,000 = .1  or 100ms. 

           

          Best wishes,

           

          Keith

          • 2. Re: Calculation for Tc
            zaid

            Thanks Sir .. You are a Legend .... makes it so easy to understand ...

            • 3. Re: Calculation for Tc
              Bahaa

              thanks  Keith,