Answer

(ii) Distance between the routers

Explanation

Transmission delay is the time required to push all packet bits onto the link:
$T_t=\frac{L}{R}$.

It depends on:

• $L$ = packet length
• $R$ = transmission rate

It does not depend on physical distance between routers. Distance affects propagation delay, which is approximately:
$T_p=\frac{d}{v}$.

Therefore, the correct answer is (ii) Distance between the routers.

Remember

Transmission delay → packet size + link rate

Propagation delay → distance + propagation speed