A modem is connected between a public telephone line and which endpoint device to enable digital data communication over analog circuits?

Introduction / Context:
Modems (modulator–demodulators) convert between a computer’s digital bitstream and the analog signals that traverse legacy telephone networks. Understanding what sits on each side of a modem clarifies how dial-up and many early WAN links functioned before native digital access became commonplace.

Given Data / Assumptions:

• One side of the modem connects to the analog telephone line (RJ-11, two-wire loop).
• The other side connects to a digital endpoint device that generates/consumes data.
• Interface to the endpoint may be via a serial port, but the endpoint itself is the computer (DTE).

Concept / Approach:
A modem sits between the telephone line and the computer (Data Terminal Equipment). The computer typically connects through an RS-232/USB interface to the modem, which in turn couples to the analog loop. Options like “serial port” name an interface type rather than the endpoint device; “network” is too vague; “communication adapter” is redundant with the modem’s role; “multiplexer” is a separate device class.

Step-by-Step Solution:

Verification / Alternative check:
Typical setups: external modems connected to PCs via RS-232 (DB-25 or DE-9) while using an RJ-11 line to the PSTN. Internal modems integrate both sides on adapter cards, but the conceptual placement remains the same—between line and computer.

Why Other Options Are Wrong:

• Network: imprecise and not the endpoint device.
• Communication adapter: essentially what a modem is; not the device beyond it.
• Serial port: an interface, not the endpoint computing device.
• Multiplexer: aggregates multiple channels; not the DTE here.

Common Pitfalls:
Equating the serial port with the computer; the port is merely the attachment interface for the computer.

Final Answer:
Computer