A packet-based scheduling algorithm for high-speed switches

The bulk of the traffic passing through a data network is made up of variable-length packets like IP packets and, therefore, the efficient handling of variable-length packets is an essential and important issue in designing a high-speed and high-performance switch. Most high-speed switches or routers using virtual output queueing as their contention resolution scheme, switch variable-length packets in the form of small and fixed-size packets (or mini-packets), such as the ATM cell, enjoying benefits in the hardware implementation and the operating speed. That is, the scheduling algorithm used in those switches is based on cell-by-cell scheduling such as PIM and SLIP. These cell-based scheduling algorithms, however, can not fully guarantee the performance metrics of an application since performance measures relevant to the application are specified by the performance metrics of its data units (packets) rather than individual mini-packets. We present an efficient algorithm called packet-based SLIP (PBSLIP) for scheduling variable-length packets on high-speed packet switches. PBSLIP is a packet-based variation of SLIP proposed by N. McKeown (1993; 1995; 1999) and, therefore, most operations of PBSLIP are as simple as those of SLIP. A conspicuous dissimilarity is that PBSLIP consecutively switches a bunch of mini-packets belonging to a given packet while SLIP switches mini-packets irrespective of their correlation to adjoining mini-packets. Extensive simulation results demonstrate that PBSLIP could be a potential way to significantly improve the performance of conventional cell-based scheduling algorithms and reduce the control time