Frame-Based Packet-Mode Scheduling for Input-Queued Switches

Most packet scheduling algorithms for input-queued switches operate on fixed-sized packets known as cells. In reality, communication traffic in many systems such as Internet runs on variable-sized packets. Motivated by potential savings of segmentation and reassembly, there has been increasing interest in scheduling variable-sized packets in a nonpreemptive manner known as packet-mode scheduling. This paper studies frame-based packet-mode scheduling for better scalability. It first shows that the admissible condition is no longer sufficient for packet-mode scheduling. Then, a relation between the frame size and packet sizes is derived that classifies under what conditions the packet-mode scheduling problem is polynomial solvable or is NP-hard. This relation reveals an interesting result that under various packet size distributions, it may be polynomial solvable even if many different packet sizes occur in the packet set, whereas it may be NP-hard with just two packet sizes present. Finally, as a practical solution, this paper studies how a speedup can help packet-mode scheduling. It is shown that the admissible condition becomes sufficient also when a speedup of two is used. A simple algorithm with a speedup of two is presented.