IP bandwidth and Nominal BW

Hello….

I have some problem that make me confused.
1. What is the difference between “IP Bandwidth” and “Nominal Bandwidth”?

2. White paper in this web tell that IP bandwidth for codec G.723.1 (6.3 kbps) is 17.07 kbps. But I read in the other reference that Nominal Bandwidth for 723.1 (6.3 kbps) is 21.9 kbps. What is the right?

3. What is the formula to count the bandwidth that used by codec?

4. In some reference I found a formula to count the bandwidth that used by voice packet:
[(payload + byte header)* bandwidth codec]/ payload
It is right?

For example: codec G 723.1 6,3 kbps and payload = 24 byte and standar header 54 byte. So the bandwidth is 78*6.3/24 = 24.475 kbps

I also measured bandwidth codec G 723.1 and I got the bandwidth is 17,17 kbps.

What is the right?

Thanks for your answer. I hope it will help me. Thanks more…