What is the primary function of a cable modem in a residential setup?

The primary function of a cable modem in a residential setup is to modulate and demodulate signals for internet access over cable TV connections. This means that the cable modem converts digital data from a computer or network into analog signals that can be transmitted over the coaxial cable system used by cable television providers. Conversely, it also converts incoming analog signals back into digital data that can be understood by devices like computers and routers.

This process enables high-speed internet connectivity using the same infrastructure that delivers cable television services. The cable modem connects to both the incoming cable line for television service and the home network, allowing for simultaneous access to internet and cable services.

While wireless internet access is often facilitated through a combined modem/router device, the core operation of a cable modem itself is focused on the modulation and demodulation functions, which make option B the correct answer.