nodes immediately transmit the packet clock signals to upstream stages and the switch nodes in the upstream stages transmit the error indication if the packet clock signals are not received over a particular link within the predefined amount of time application_number US 74950085 A description fig1 illustrates a packet switching system for switching packets from an originating trunk controller such as trunk controller 104 to a destination trunk controller such as trunk controller 107 packet switching network 101 comprises a plurality of switching stages which ilustratively may be four and each switching stage has a plurality of switch nodes each switch node is interconnected to two nodes in the downstream stage by means of two individual links each individual link consists of two conductors the first conductor is utilized by the downstream switch node to transmit clock signals to the upstream node when the downstream node has the capacity for accepting a packet from the upstream node when the upstream node has a packet to transmit it utilizes the clock signals to transfer the packet to the downstream node an inter stage protocol is utilized to detect the malfunction of a downstream node or the malfunction of the inter stage link if a node within a stage detects the malfunctioning of a downstream node or the inter stage link it communicates this information to error detector circuit 134 for example a downstream node in the second stage transmits an error signal via conductor 131 error detector circuit 134 is responsive to the receipt of the error signal on conductor 131 to transmit the fact that an error has occurred in the second stage via bus 135 to central processor.