Dual priority switching apparatus for simplex networks

Abstract

A high priority path is added to the normal low priority path through a multi-stage switching network. The high priority path is established at the quickest possible speed because the high priority command is stored at the switch stage involved and made on a priority basis as soon as an output port becomes available. In addition, a positive feedback is given to the node establishing the connection immediately upon the making of the connection so that it may proceed at the earliest possible moment. The high priority path is capable of processing multiple high priority pending requests, and resolving the high priority contention using a snapshot register which implements a rotating priority such that no one requesting device can ever be locked out or experience data starvation. A dual priority switching apparatus with input port connections to output port connections uses as asynchronous means to resolve contention under low priority and the absence of blockage conditions, and switches automatically to a priority driven synchronous means of resolving contention. The protocol requires several parallel data lines plus four control lines so that the switching apparatus can be used for networks having a plurality of nodes, each node having a plurality of input and output ports, with a multiplexer control circuit for each output port for connecting any of I inputs to any of Z outputs, where I and Z can assume any unique value greater or equal to two. The switch has a single physical network path element over which either a low priority or high priority path can be established.