Nodes A and B are D$1=4,000$km apart and nodes B and C are D$2=300$km apart. The data rate between A and B is Rab $=175,000$ bps$.$ Both links are fibre. The links are full duplex with frame size of L $=1,500$ bits. A to B uses sliding windows with a window size of W$,$ and B to C is stop and wait. There are no errors. $2$

i$)$

Calculate W $($round down to an integer$)$ for as near as possible to $100\%$ transmission efficiency between A and B$.$

ii$)$ Calculate the efficiency of transmission over the link BC to the nearest integer $\%.$