Two-by-two switch element enables formation of rings and other nocs.
Switch element is registered: hence network can span the chip.
Network needs to carry decoupled requests and response packets.
Local arbitration in each element. Global policies required to avoid deadlock and starvation.
Give priority to traffic already on the ring: LAN-like buffering at source.
Does not carry interrupts or other sideband signals.
Single ring: throughput=2. counter-rotating ring: throughput=4.