Historically for dial-up and serial data communications, which bit rates (in bps) became the most commonly used standard speeds—among the given individual choices, which represents the widely adopted higher-rate baseline?

Introduction / Context:
Serial and dial-up modems evolved through a sequence of standardized bit rates. While very low speeds enabled early data links, later standards achieved higher throughput and became the practical baseline for reliable, widespread communications before even faster protocols emerged. Recognizing these landmark rates helps make sense of legacy configurations and exam questions.

Given Data / Assumptions:

• The options list classic discrete bps rates: 300, 1200, 2400, and 9600.
• We select the most commonly used higher-rate baseline that dominated general-purpose modem use for years.
• Context is human-to-computer dial-up and serial links prior to V.34/V.90.

Concept / Approach:
While 300, 1200, and 2400 bps were milestones, 9600 bps (for example, V.32) became a widely adopted standard speed across dial-up and serial console connections. It provided a practical balance between speed and line quality requirements, and many devices shipped with 9600 bps as the default console speed. Therefore, among the single-rate choices provided, 9600 best represents the commonly used higher baseline that displaced earlier, slower rates.

Step-by-Step Solution:

Verification / Alternative check:
Check router/switch console documentation and legacy modem guides showing 9600 bps as the default configuration, corroborating its widespread usage.

Why Other Options Are Wrong:

• 300/1200/2400: Historically important but largely superseded; not the enduring higher-rate baseline.
• None of the above: Incorrect because 9600 is a well-known common standard speed.

Common Pitfalls:
Interpreting “most commonly used speeds” as a set; this question asks you to choose one rate among discrete options. In practice, environments used many rates, but 9600 became the de facto default for serial consoles and many dial-up links.

Final Answer:
9600