Allocation of node transmissions in switching networks used with scalable coherent interfaces

The Scalable Coherent Interface (SCI) standard of the Institute of Electrical and Electronics Engineers is intended for fast, high throughput, point-to-point, unidirectional links to high-performance multiprocessor systems. Key elements of the protocol for SCI are the (a) idle.cc which are idle bits circulation to be inserted between packets transmitted in an SCI network for detecting lost packets which toggles when the idle bit circulation has circulated around the ringlet; and (b) idle.ac, or allocation bit which is a bit in a group of transmitted idle bits which toggles when all operational nodes in an SCI network have had an opportunity to transmit their data packets. All switches accumulate transitions of the allocation bits to a value that is different from the current remembered allocation value on each enabled input port. If the network is out of allocation bit synchronization at a switch when a second transition of allocation bit occurs on an input port of the switch, the transition is ignored. The switch declares agreement when all input ports have made at least one transition even though the current allocation bit values at the input ports are not in agreement. This procedure allows rows that are one idle allocation value behind to advance their value while preventing the other rows from advancing their value, which enables resynchronization of idle allocation values after network idle allocation synchronization has been lost. All non-output stage switches toggle the current value of the allocation bit when all enabled output ports of the switch have transmitted the current allocation bit value and all enabled input ports have transitioned as explained above. This guarantees that the current agreement is broadcast on all output ports before a new value allocation can be accepted.