Data link layer Sliding Window utilization formula query
If it is about how we got to the formula, link utilization is the ratio of the time that the link is active to the total time.

total time being the sum of transmission time and propagation time.
link active time = time taken to transmit N packets = N * TransmissionDelay

Hence, the formula to calculate link utilization(or efficiency) is

N/(1+2a)

However, in practice, the link utilization cannot exceed 1 (ie link cannot be active for more than 100% of the time).
Hence, whenever N&gt;(1+2a), we restrict the value to 1 only.