37 Design, manufacturing, installation, testing, and maintenance of (a) switching products, namely digital telephone switches, add-on frames, line cards and circuit boards for telecommunications service providers; (b) transport products, namely intelligent multiplexers, protection switches, mini-repeater housings, frame controllers, asynchronous and fractional data cards, microwave and millimeterwave radio equipment and modems; (c) telecommunication and cable system access products, namely digital loop carriers, telemetry equipment, modems and wireless local loop equipment, namely antenna and radio port control units; refurbishment and upgrade of pay telephone units, and refurbishment, upgrade, repair and maintenance of related pay telephone products, namely stainless steel and custom logo vault doors, handsets and volume amplifiers