In a stop-and-wait ARQ, the bandwidth-delay product determines the maximum number of unacknowledged frames that can be in transit at any given time. In this case, the bandwidth-delay product is 20,000 bits, which means that at any given time, there can be up to 20,000 bits worth of data in transit.
If the frame size is 1000 bits, and the protocol allows 15 frames to be sent without waiting for acknowledgement, then the total number of bits in transit would be 15 * 1000 = 15,000 bits.
To calculate the percentage of utilization of the link, we can divide the number of bits in transit by the bandwidth-delay product and multiply by 100 to express the result as a percentage:
utilization = (15,000 bits / 20,000 bits) * 100% = 75%
Therefore, the percentage of utilization of the link would be 75%.