Consider a token bucket with maximum rate R = 20*(10^6) bps
suppose we want to make sure that the maximum rate can only be sent for at-most 10 seconds at a time , and at- most ( maximum ) 150 Mb can be sent over any 15 second window.
Then the required value for which the new tokens are added at the rate of r Mbps which we have to calculate in this question .
Capacity of the token bucket (b) = 150 Mbps
Maximum possible transmission rate (M) = 20*(106) bps
So the maximum burst time = b/(M-r) = 10
Duration = b/M-r, where b is the initial capacity, M is outgoing rate and r is incoming rate
now put b= 150 Mbps, M = 20 Mbps , we need to find r
b= (M-r) 10
b = 10M - 10r
10r = (200 - 150 )
r = 50 /10
r = 5
The value for token input rate is 5 Mbps