Abstract: A network switch which can perform in respect of addressed data packets source address and destination address look-ups in a forwarding database includes a control which inhibits the performance of source address look-ups if the length of a respective receive queue of packets is greater than a threshold. The inhibition may endure until the length of the receive queue falls below a second threshold lower than the first.

Abstract: A stackable network unit comprises a ‘down’ port and an ‘up’ port, an arbitration path for data packets from the down port to the up port, a repeat path for data packets from the up port to the down port, a link detector for detecting tile absence of another operative unit connected to the down port to cause data packets on the return pat to bypass the down port and proceed on the arbitration path and for detecting the absence of another operative unit connected to the up port to cause data packets on the arbitration path to bypass the up port and proceed on the repeat path.

Abstract: A socket connector has a single socket including fiber optic terminals 10 and wire terminals 12 and is adapted to receive alternatively in respectively inverted positions either a first plug connector for cooperation with the fiber optic terminals or a second plug connector for cooperation with the wire terminals, in each case without engagement with the terminals with which the plug should not cooperate. The connector includes respective latching slots 7 and 11 in opposite walls 5 and 3 for the respective plug connectors.