Multicast support in multi-chip centralized schedulers in Input Queued switches

IQ switches store packets at input ports to avoid the memory speedup required by OQ switches. However, packet schedulers are needed to determine an I/O (Input/Output) interconnection pattern that avoids conflicts among packets at output ports. Today, centralized, single-chip, scheduler implementation are largely dominant. In the near future, the multichip scheduler implementation will be suited to reduce the hardware scheduler complexity in very large, high-speed, switches. However, the multi-chip implementation implies introducing a non-negligible delay among input and output selectors used to determine the I/O interconnection pattern at each time slot. This delay, mainly due to inter-chip latency, requires modifications to traditional scheduling algorithms, which normally rely on the hypothesis that information exchange among selectors can be performed with negligible delay. We propose a novel multicast scheduler, named IMRR, an extension of a previously proposed multicast scheduling algorithm named mRRM, making it suitable to a multi-chip implementation, and examine its performance by simulation.