The Christmas-tree switch: an output queuing space-division fast packet switch based on interleaving distribution and concentration functions

A self-routing space-division fast packet switch architecture is proposed which achieves output queuing with a reduced number of internal paths (O(N)). The switch architecture is a multi-level binary tree in which each branch constitutes a group of paths that are shared by all the packets destined to a subset of output ports. The reduction in the number of internal paths is obtained by interleaving the packet distribution and packet concentration functions throughout the switch fabric. Packet loss may occur at each level of the tree and is dependent on the degree of concentration exercised at that level. Owing to the binary tree structure of the switching fabric, a simple mathematical analysis is performed in order to determine the concentration parameters appropriate for each level. Several implementation architectures based on sorting networks are described