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Propagation Delay

The propagation delay is the time it takes for a signal to propagate. It depends on the distance traveled, and the specific propagation speed of the medium. For instance, information transmitted via radio or through copper cables will travel at a speed close to c (speed of light in vacuum, ~300000 km/s). The prevalent medium for long-distance digital transmission is now light in optical fibers, where the propagation speed is about 2/3 c, i.e. 200000 km/s.

Propagation delay, along with serialization delay and processing delays in nodes such as routers, is a component of overall delay/RTT. For uncongested long-distance network paths, it is usually the dominant component.


Here are a few examples for propagation delay components of one-way and round-trip delays over selected distances in fiber.

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Fibre length

One-way delay

Round-trip time


5 ns

10 ns


5 µs

10 µs


50 µs

100 µs


500 µs

1 ms


5 ms

10 ms


50 ms

100 ms

– Main.SimonLeinen - 28 Feb 2006

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