Abstract-- The problem of providing quality of service guarantees for multicast traffic over crossbar switches has received a limited attention, despite the popularity of its counterpart for unicast traffic. Providing a 100% throughput to all admissible multicast traffic has been shown to be very difficult task and it requires a very high speedup in the switching fabric. In this paper, we introduce the concept of rate quantization and use rate quantization to show an analogy between packet scheduling in crossbar switches and circuit switching in three-stage Clos networks. We exploit the analogy to adopt circuit switching algorithms in wide sense and strict sense non-blocking Clos networks in order to construct non-blocking packet schedulers for unicast and multicast traffic. We illustrate a simple multicast non-blocking packet scheduler, for which a speedup of 6 log n/ log log n is sufficient to support 100% throughput for any admissible multicast traffic in an n