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Abstract-This paper studies input-queued packet switches loaded with both unicast and multicast traffic. The packet switch architecture is assumed to comprise a switching fabric with multicast (and broadcast) capabilities, operating in a synchronous slotted fashion. Fixed-size data units, called cells, are transferred from each switch input to any set of outputs in one time slot, according to the decisions of the switch scheduler, that identifies at each time slot a set of nonconflicting cells, i.e., cells neither coming from the same input, nor directed to the same output.First, multicast traffic admissibility conditions are discussed, and a simple counterexample showing intrinsic performance losses of input-queued with respect to output-queued switch architectures is presented. Second, the optimal scheduling discipline to transfer multicast packets from inputs to outputs is defined. This discipline is rather complex, requires a queuing architecture that probably is not implementable, and does not guarantee in-sequence delivery of data. However, from the definition of the optimal multicast scheduling discipline, the formal characterization of the sustainable multicast traffic region naturally follows. Then, several theorems showing intrinsic performance losses of input-queued with respect to output-queued switch architectures are proved. In particular, we prove that, when using per multicast flow FIFO queueing architectures, the internal speedup that guarantees 100% throughput under admissible traffic grows with the number of switch ports.

OpenFlow is an open standard that can be implemented in Ethernet switches, routers and wireless access points (AP). In the OpenFlow framework, packet forwarding (data plane) and routing decisions (control plane) run on different devices. OpenFlow switches are in charge of packet forwarding, whereas a controller sets up switch forwarding tables on a perflow basis, to enable flow isolation and resource slicing. We focus on the data path and analyze the OpenFlow implementation in Linux based PCs. We compare OpenFlow switching, layer-2 Ethernet switching and layer-3 IP routing performance. Forwarding throughput and packet latency in underloaded and overloaded conditions are analyzed, with different traffic patterns. System scalability is analyzed using different forwarding table size, and fairness in resource distribution is measured.

Abstract-We consider input-queued switch architectures dealing at their interfaces with variable-size packets, but internally operating on fixed-size cells. Packets are segmented into cells at input ports, transferred through the switching fabric, and reassembled at output ports. Cell transfers are controlled by a scheduling algorithm, which operates in packet-mode: all cells belonging to the same packet are transferred from inputs to outputs without interruption. We prove that input-queued switches using packet-mode scheduling can achieve 100% throughput, and we show by simulation that, depending on the packet size distribution, packet-mode scheduling may provide advantages over cell-mode scheduling.Index Terms-Input queued switched, packet switching, scheduling algorithms, variable size packets.

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