A stop-and-wait protocol is used to send frames over a 4 Kbps link.

Assuming the link is 40 km and signal propagates with the speed of

2*10^8 m/s, for what range of frame sizes the protocol achieves an efficiency

of at least 50%?

(Assume that the frame and ACK creation times are

negligible, frames contain only data and no

overhead, and ACK transmission time could be ignored).