In data communications, modulation is the process of altering a carrier wave so that it conveys digital information by representing bits as analog signal variations for transmission over analog media.

Introduction:
Modulation is a foundational concept in data and telecommunication systems that enables computers and other digital devices to send information across channels originally designed for analog signals (e.g., radio, telephone lines).

Given Data / Assumptions:

• A digital bitstream must traverse an analog physical medium.
• A sinusoidal carrier (characterized by amplitude, frequency, and phase) is available.
• Receiver and transmitter share a compatible modulation/demodulation scheme.

Concept / Approach:
Modulation maps digital bits to changes in a carrier wave: amplitude (ASK), frequency (FSK), or phase (PSK). This process effectively converts digital signals to analog signals suitable for the channel. At the receiving end, demodulation reverses the process to recover the original bitstream.

Step-by-Step Solution:
1) Start with digital data (bits).2) Choose a modulation scheme (e.g., BPSK, QPSK, QAM).3) Vary carrier parameters according to bit patterns to produce an analog waveform.4) Transmit the modulated analog signal; receiver demodulates to reconstruct bits.

Verification / Alternative check:
Observe that analog phone lines and RF channels require analog waveforms. Practical systems (DSL, Wi-Fi, cellular) all modulate carriers to embed digital information.

Why Other Options Are Wrong:

• Converting analog to digital: that is sampling/quantization/ADC, not modulation.
• Multiplexing: combines multiple signals but does not impose data onto a carrier.
• Encryption: secures data but does not change physical signal form.
• Error-correcting coding: adds redundancy; still distinct from the carrier alteration process.

Common Pitfalls:
Confusing modulation with encoding or multiplexing. Modulation changes the carrier; encoding changes bit patterns; multiplexing shares bandwidth among flows.

Final Answer:
Converting digital signals to analog signals