In data communications, which device aggregates simultaneous transmissions from multiple input/output (I/O) devices onto a single communication line?

Introduction:
Many communication scenarios require combining several lower-rate streams for transport over a higher-capacity link. The device that performs this combination reduces cabling, increases efficiency, and lowers cost. This question asks you to identify that device from common networking terms.

Given Data / Assumptions:

• Multiple I/O sources produce data that must share one line.
• The line supports higher capacity than each individual source requires.
• Terminology includes both accurate and distractor options.

Concept / Approach:
A multiplexer (MUX) combines multiple input signals onto a single output channel using time-division (TDM), frequency-division (FDM), or statistical multiplexing, depending on the technology. At the far end, a demultiplexer (DEMUX) separates the streams. While the term “concentrator” is sometimes used in telephony/data networks, “multiplexer” is the canonical device that aggregates signals at the physical/link level for a single line.

Step-by-Step Solution:

Verification / Alternative check:
Examples include T1/E1 multiplexers (time slots), optical WDM systems (wavelength slots), and statistical multiplexers for packet streams, all reaffirming the MUX role.

Why Other Options Are Wrong:

• Concentrator: can refer to certain aggregation devices but is less precise than multiplexer for a single-line combination at the physical/link level.
• Modifier: not a standard communications device name.
• Full-duplex line: describes a link's capability, not an aggregating device.
• None of the above: incorrect because multiplexer is correct.

Common Pitfalls:
Confusing general aggregation terms with the specific MUX/DEMUX pair; assuming full-duplex implies aggregation (it does not).

Final Answer:
Multiplexer.