telephone-related signaling and transmission products including digital systems products, data communication products, and voice transmission products, such digital systems products comprising digital cross-connects, voice transcoders, [T1 channel service units,] and digital echo cancellers; such data communication products comprising packet switches, statistical multiplexers, network monitoring software and systems composed of computers, computer peripherals, and computer programs, and [ T1 networking multiplexers and nodal switches; such voice transmission products comprising line amplifiers and repeaters, remote-align data station termination and network channel terminating modules, distributive data bridging modules, signaling and signaling conversion modules, power and ringing supplies, conferencing/alerting modules, selective signaling and teleconferencing modules,] metal and plastic mounting shelves, apparatus cases, and prewired assemblies