A Knockout Switch for Variable-Length Packets

Abstract

The Knockout Switch is a new packet switch architecture recently proposed for high-speed local and metropolitan area networks, multiprocessor interconnects, and local or toll switches for integrated traffic loads. We describe an approach to extend the original Knockout Switch to work with variable-length packets. This new architecture employs an input broadcast bus arrangement to achieve complete interconnection of the inputs and outputs. Consequently, there is no congestion in the switch fabric other than the unavoidable conflict of multiple simultaneous packets destined for the same output. It is with this output contention that the Knockout principle is fully utilized to efficiently concentrate and store contending packets while maintaining the first-in first-out discipline of the packet sequence; and yet the fabric speed required is no more than the input/output line speeds, Under these design goals, no switch can yield better delay/ throughout performance. These are the most important attributes that have been preserved in the current proposal from the original Knockout Switch. For an N \times N switch configuration, the variable-length packet Knockout Switch consists of N input broadcast buses, and an N:L concentrator ( L \ll N ) and a shared buffer for each output. The design of each subsystem is discussed with emphasis on possible VLSI realization. Using today's technology, we should be able to implement the proposed switch with both input/output lines and internal hardware operating at 50 Mbits/s. The dimension of the switch ( N \times N ) can grow modularly from say 32 × 32 to 1024 × 1024, rendering a total throughput in the range of tens of gigabits per second. Future upgrading of the line interfaces to much higher speed without modification to the internal switch hardware is also possible with a modest restriction on the minimum length of new packets.