Modem data transfer — Which transmission method do dial-up modems most commonly use for character data?
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ASynchronous
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BAsynchronous
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CTimed interval (non-standard)
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DPPP (a protocol, not a physical transmission method)
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ENone of the above
Answer
Correct Answer: Asynchronous
Explanation
Introduction / Context:Legacy dial-up modems historically carried serial data over analog phone lines. Knowing whether transmission is synchronous or asynchronous clarifies line coding, framing, and UART behavior.
Given Data / Assumptions:
- Standard external/internal modems attached to COM ports (RS-232).
- Typical terminal/serial communication with start/stop bits.
- PPP is a link-layer protocol encapsulated over the serial link.
Concept / Approach:
Asynchronous serial communication frames each character with start/stop bits. This matches how UARTs and COM ports operate for dial-up access. While some specialized modems support synchronous modes, general PC use is asynchronous.
Step-by-Step Solution:
Identify the physical layer method used by COM port modems: async serial with start/stop bits.Recognize PPP runs over this link but is a protocol, not the electrical transmission method.Select “Asynchronous” as the correct transmission method.Verification / Alternative check:
Serial port settings (8N1, baud) and UART operation confirm asynchronous framing is standard for dial-up PC setups.
Why Other Options Are Wrong:
Synchronous is less common for PC dial-up; “Timed interval” is not a standard; PPP describes link framing and negotiation layered over the serial method.
Common Pitfalls:
Confusing physical transmission characteristics with higher-layer protocols; assuming PPP implies synchronous signaling.
Final Answer:
Asynchronous.