Satellite telephony delay: A user speaking via a single geostationary satellite normally experiences a round-trip conversational delay of about how many milliseconds (ms) before hearing the other person’s reply?

Introduction / Context:
GEO satellite telephony introduces noticeable latency because signals must travel from ground to satellite and back down, typically twice in a two-way conversation. Understanding the typical conversational delay helps designers and users set expectations for voice quality and echo management.

Given Data / Assumptions:

• Geostationary altitude ~35,786 km.
• Speed of EM waves ~3 x 10^8 m/s.
• Single GEO hop path: ground → satellite → ground.

Concept / Approach:

One-way propagation for a single hop is roughly 120–140 ms depending on geometry. A round-trip conversational exchange (there and back) is thus near 240–280 ms. In practice, switching/routing adds small extra delays, so ~250–300 ms is commonly quoted. Therefore, 270 ms is the best representative answer among the choices.

Step-by-Step Solution:

Verification / Alternative check:

Telecom guidelines and textbooks often quote ~250–300 ms end-to-end for GEO satellite voice, in line with this estimate.

Why Other Options Are Wrong:

• 100 ms: too optimistic; even one-way is commonly >100 ms.
• 470 ms, 540 ms: higher than typical single-hop conversational round-trip; such numbers suggest multiple hops or additional delays.

Common Pitfalls:

Confusing one-way and round-trip delays, or mixing terrestrial network delays with satellite propagation delay.

Final Answer:

270 ms