What technology uses existing cable TV infrastructure for internet service?

The technology that utilizes existing cable TV infrastructure for internet service is Hybrid Fiber-coaxial (HFC). HFC networks combine both fiber optic and coaxial cable technologies, allowing for high-speed internet delivery while leveraging the extensive cable infrastructure already in place.

Cable connections are indeed part of the technology, but they don't specifically define the system as HFC does. HFC uses fiber optics for the main transmission lines and coaxial cable for distribution to individual subscribers, optimizing the efficiency and speed of the internet service over what traditional coaxial connections alone could provide.

Fiber optics and ADSL are distinct types of technology; fiber optics focuses on providing internet and data through light signals in fiber cables, whereas ADSL utilizes traditional telephone lines for internet transmission and operates differently than cable networks. HFC is an important innovation in broadband delivery, encapsulating both fiber optic and coaxial aspects, which is why it is the most accurate choice for this question.