Propagation delay in geosynchronous satellite links What is the approximate maximum signal propagation time (end-to-end round-trip delay) in a GEO satellite transmission, accounting for up-and-down paths via the satellite?

Introduction / Context:
GEO satellite links exhibit noticeable latency because signals must travel about 36,000 km up to the satellite and back down to Earth—often twice (uplink and downlink in each direction). Understanding this delay is vital for voice, data, and interactive applications over satellite links.

Given Data / Assumptions:

• Speed of electromagnetic waves ~3 x 10^8 m/s in free space.
• One-way GEO hop (ground → satellite → ground) ≈ 2 x 35,786 km of vacuum path plus slant geometry.
• Round-trip (two GEO hops in a conversation) is roughly twice the one-way hop delay.

Concept / Approach:

A typical one-way end-to-end GEO path is on the order of 250–280 ms depending on geometry. The round-trip time (RTT) is then approximately double, around 500–560 ms. Industry shorthand often quotes ~540 ms as a representative maximum end-to-end delay for GEO links.

Step-by-Step Solution:

Verification / Alternative check:

Network measurements over GEO confirm about half-second RTT under typical conditions.

Why Other Options Are Wrong:

270 ms (b) is closer to a one-way delay; 135 ms (c) is too small; 1080 ms (d) is roughly double RTT; 50 ms (e) reflects terrestrial or LEO links, not GEO.

Common Pitfalls:

Confusing one-way and round-trip delays; ignoring processing delays, which add modestly to propagation time.

Final Answer:

540 milliseconds