Smart modems: a smart modem can automatically dial, hang up, and answer incoming calls. Which component typically issues the commands that instruct the modem to perform these actions?

Introduction / Context:
Smart modems implement command sets (famously the AT command set) so that a host can control dialing, answering, and hanging up. Understanding who sends those commands clarifies the division of responsibility between hardware and software in dial-up or serial-based communications.

Given Data / Assumptions:

• The modem supports a command interface (e.g., ATD for dial, ATA for answer, ATH for hang up).
• The host has an application capable of issuing these commands via a serial or virtual COM port.
• Protocols and procedures operate after link establishment; they do not originate dial commands by themselves.

Concept / Approach:
Communications software (terminal programs, dialers, remote access clients) sends human-initiated or automated commands to the modem. Error-detecting protocols (like V.42) and link procedures (like LAP) manage framing/reliability post-connect; they do not direct the modem to start or end calls. “Telecommunications” is a broad field, not a controlling component.

Step-by-Step Solution:

Verification / Alternative check:
Classic tools (HyperTerminal, minicom, PPP dialers) demonstrate programmatic dialing and hangup through command sequences scripted by the software.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming the modem autonomously decides when to dial; in practice, the host application triggers these actions.

Final Answer:
Communications software.