Suppose two hosts are connected by a point-to-point link and they are configured to use Stop-and-Wait protocol for reliable data transfer. Identify in which one of the following scenarios, the utilization of the link is the lowest.

In the Stop-and-Wait protocol, the efficiency or link utilization ($\eta$) is given by:

where:

• $T_t = \frac{L}{B}$ is the transmission time ($L$ is frame size, $B$ is bandwidth / transmission rate)

• $T_p = \frac{d}{v}$ is the propagation time ($d$ is link length, $v$ is propagation speed)

• $a = \frac{T_p}{T_t} = \frac{d \cdot B}{v \cdot L}$

To make link utilization $\eta$ the lowest (minimum), the parameter $a$ must be maximized.

Since $a \propto d \times B$, $a$ is maximized when:

1. The link length ($d$) is longer.

2. The transmission rate ($B$) is higher.

Therefore, the link utilization is lowest for Longer link length and higher transmission rate (Option B).