Consider the scenario shown below, with four different servers connected to four different clients over four three$-$hop paths. The four pairs share a common middle hop with a transmission capacity of R $=100$ Mbps$.$ The four links from the servers to the shared link have a transmission capacity of RS $=100$ Mbps$.$ Each of the four links from the shared middle link to a client has a transmission capacity of RC $=40$ Mbps per second.

Which link is the bottleneck link?