In data communications, the hardware device that functions as a switching and connecting unit—selecting one of several input lines to share a single communication path—is called a multiplexer (MUX).

Introduction / Context:
Many devices must share limited communication links. A multiplexer (MUX) combines multiple signals for transmission over a single medium by time, frequency, or code division. It therefore acts as both a connecting element (interfacing multiple sources) and a switching element (selecting among them) according to a defined scheme.

Given Data / Assumptions:

• Multiple low-speed or parallel sources must utilize one higher-capacity line.
• Selection and combination rules are defined (e.g., time slots in TDM).
• We differentiate MUX from other comms components.

Concept / Approach:
A MUX connects N inputs to one output using a switching strategy. The inverse device is a demultiplexer (DEMUX). A concentrator aggregates traffic but often includes buffering and protocol handling; RS-232C is an electrical interface standard; a communications processor is a broader intelligent device (e.g., a front-end processor) that may perform protocol conversion and routing beyond mere multiplexing.

Step-by-Step Solution:
Identify the function: select/combine multiple inputs onto a single path.Match the function to device type: multiplexer.Exclude alternatives based on definitions and scope.

Verification / Alternative check:
Telecom systems widely use TDM multiplexers to share trunks among many voice/data channels, confirming the role as switching/connecting equipment.

Why Other Options Are Wrong:
Concentrator: aggregates traffic but not strictly a MUX switching function.RS-232C port: a serial interface standard, not a switching unit.Communications processor: broader intelligent device, beyond simple multiplexing.None of the above: incorrect because “Multiplexer” fits exactly.

Common Pitfalls:
Confusing physical layer standards with devices; assuming any aggregator is a MUX even when it performs protocol processing or routing.

Final Answer:
Multiplexer