The techniques and technologies used to modernize a network, machine or device. In cable parlance, “upgrade” generally means replacing the guts of an amplifier with higher-bandwidth modules, capable of supporting bidirectional (two-way) traffic. That’s contrasted with a “rebuild,” in which old plant is torn away, and new plant/electronics installed, and a “line extension,” which is a new build into, say, a new housing development.
Cable, for the most part, is finished with the “rebuild” part of its life, but continues to have bandwidth expansion options from transmission equipment suppliers. One option is to replace amplifier innards with 1 GHz components, for instance, although that move necessitates tuners that go above 870 MHz.