A selective-repeat (SR) data link layer protocol uses 4 sequence bits to number it's frames. The source, C starts from frame 0 and proceeds following the Sr protocol. Let us start analyzing the frame/ACK transmissions when the first outstanding frame is Frame 3, kneeing that all previous frames have been received by destination, D with no errors detected. C sends four more frames (including frame 3) and then it's timer expires. C proceeds according to the SR policies and right after it has sent only one frame responding to NAK4, it receives an ACK 7. C then continues until all the frames in the window are outstanding. Ignore any processing and queuing delay. Assume propagation delay is equal to transmission delay of data Frames, however ignore the transmission delay of control frames.
a) calculate the range of frame sequence njmbers
b) illustrate all frame and ACK transfers properly for the set of events explained, however for simplicity show the send and receive windows only for 3 time instances:
1. The beginning when the first outstanding frame is frame 3
2. Right when C gets a timeout
3 shortly after C has received ACK7