Hello Ayong
Here’s a summary of the mathematics:
- CIR is the committed information rate, which is the number of bits per second which is the data rate agreed upon between the ISP and the customer.
- Tc is the time interval used for calculations. In this lesson, Tc = 50ms
- Bc is the committed burst rate. This is the number of bits that will be sent every Tc, based on the CIR
- Be is the excess burst rate, which is the additional bits per Tc that we will allow under certain conditions. In this lesson, the Be is the difference between the interface rate (AR) and Bc.
- The AR is the access rate, which in this lesson is 1536 Kbps or 1,536,000 bps.
In the lesson, Tc = 50ms, and CIR = 512 Kbps = 512,000 bps for DLCI 102. Therefore:
- there are 1000 ms / 50 ms = 20 Tcs within a second
- Bc = CIR / 20 = 512,000 bps / 20 = 25,600 bits per Tc
- Be = AR - Bc = 1,536,000 bps -
Now how many bits are sent every Tc at the AR rate, that is, the rate of the interface itself? Since Tc = 50ms, we use the same logic as above, and we do the following:
- there are 1000 ms / 50 ms = 20 Tcs within a second
- Bits sent every Tc at the AR rate = 1,536,000 bps / 20 = 76800 bits per Tc
- Be = 76,800 bits per Tc - Bc = 76,800 bits per Tc - 25,600 bits per Tc = 51,200 bits
You can follow the same logic to find the Be for the other DLCI.
I hope this has been helpful!
Laz