Data frames are generated at nodes A and D and sent to node C through node B, as shown in the figure. Determine the minimum transmission rate required between nodes B and C such that the buffers of node B are not flooded; to avoid flooding of Bs buffers, the average number of frames entering and leaving B must be the same over a long time interval. The transmission rate between A and B is 100kbps, and the distance between them is 4000km. A and B communicate using a sliding window protocol with a window size of 3 frames. The transmission rate between B and D is 50kbps, and the distance between them is 2000km. B and D communicate using a stop-and-wait protocol. The distance between B and C is 1000km, and they communicate using a sliding window protocol with a window size of 4 frames. The links are full-duplex and the propagation delay is 0.005ms/km for all of them. All data frames are 1000bits long; ACK frames are separate frames of negligible size. Assume all the frames are received correctly.

A - B - C

I

D