In terminal communication, if both local echo and remote echo are enabled, how many times will each typed character appear on the user's screen?

Introduction / Context:
In data communications, echo refers to the immediate display of typed characters. Understanding local and remote echo behavior is essential for diagnosing duplicate or missing characters in terminal sessions.

Given Data / Assumptions:

• Local echo means the terminal itself displays characters as typed.
• Remote echo means the host echoes characters back to the terminal.
• Both are enabled simultaneously.

Concept / Approach:

If both local and remote echo are active, each keystroke is displayed twice: once by the local terminal and once by the remote host. This causes duplication, making text appear doubled.

Step-by-Step Solution:

Verification / Alternative check:

Test with telnet where echo settings can be toggled. Observe output with only local, only remote, and both enabled.

Why Other Options Are Wrong:

• Once: true only if one echo (local or remote) is active.
• Three times: excessive; only two echoes occur.
• Never: false; at least one echo always shows text.
• None: incorrect because 'twice' is correct.

Common Pitfalls:

• Assuming both echoes cancel each other—they do not, they duplicate output.
• Confusing echo issues with line buffering.

Final Answer:

twice.