When does the initialization process of a DOCSIS modem begin?

The initialization process of a DOCSIS modem begins automatically when it is powered up and connected. This automatic start is intrinsic to the modem's design; it begins the necessary series of self-diagnostics and attempts to establish a connection with the network without requiring any manual intervention or prior user configuration.

Upon powering up, the modem scans for the signal from the service provider, which allows it to proceed with the initialization process, including tasks such as registering on the network, acquiring an IP address, and downloading configuration files needed for operation. The other options suggest a dependency on either physical connection state or specific input actions, which aren't required for the automatic initialization sequence to occur. Thus, the correct answer reflects the modem's capability to initiate independently upon receiving power and a compatible connection to the network.