Where to provide support for efficient multicasting in irregular networks: network interface or switch?

Recent research has proposed methods for enhancing the performance of multicast in networks with irregular topologies. These methods fall into two broad categories: (a) network interface (NI) based schemes that make use of enhanced functionality of the software/firmware running at the NI processor; and (b) switch-based methods that use enhancements to the switch architecture to support hardware multicast. However it is not clear how these methods compare to each other and when it makes sense to use one over the other. In order to answer such questions, we perform a number of simulation experiments to compare the performance of three efficient multicasting schemes: an NI-based multicasting scheme that uses a k-binomial tree, a switch-based multicasting scheme that uses path-based multidestination worms, and a switch-based multicasting scheme that uses a single tree-based multidestination worm. We first study the performance of the three schemes for single multicast traffic while changing a number of system parameters one at a time to isolate their impact. We then study the performance of these schemes under increasing multicast load. Our results show that the switch-based multicasting scheme using a single tree-based multidestination worm performs the best among the three schemes. However the NI-based multicasting scheme is capable of delivering high performance compared to the switch-based multicast using path-based worms especially when the software overhead at the network interface is less than half of the overhead at the host. We therefore conclude that support for multicast at the NI is an important first step to improving multicast performance. However; there is still considerable gain that can be achieved by supporting hardware multicast in switches. Finally, while supporting such hardware multicast, it is better to support schemes that can achieve multicast in one phase.