  Packet-switching WDM ring networks with a hotspot transporting unicast,
multicast, and broadcast traffic are important components of high-speed
metropolitan area networks. For an arbitrary multicast fanout traffic model
with uniform, hotspot destination, and hotspot source packet traffic, we
analyze the maximum achievable long-run average packet throughput, which we
refer to as \textit{multicast capacity}, of bi-directional shortest-path routed
WDM rings. We identify three segments that can experience the maximum
utilization, and thus, limit the multicast capacity. We characterize the
segment utilization probabilities through bounds and approximations, which we
verify through simulations. We discover that shortest-path routing can lead to
utilization probabilities above one half for moderate to large portions of
hotspot source multi- and broadcast traffic, and consequently multicast
capacities of less than two simultaneous packet transmissions. We outline a
one-copy routing strategy that guarantees a multicast capacity of at least two
simultaneous packet transmissions for arbitrary hotspot source traffic.
