Question :
What is the propagation delay from R1 to R2 - the amount of time from when the first bit of a packet is transmitted at R1, until it is received at R2?
What is the transmission time of the packet at R1 (the time from when the first bit of the packet is sent into the wire, and the time at which the last bit is sent into the wire)?
Now assume that the link lengths are changed.
How long should the link be so that R2 is receiving the first bit of a packet at the same time R1 is sending out the last bit of the same packet?