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.
Examples
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 |
---|---|---|
1m |
5 ns |
10 ns |
1km |
5 µs |
10 µs |
10km |
50 µs |
100 µs |
100km |
500 µs |
1 ms |
1000km |
5 ms |
10 ms |
10000km |
50 ms |
100 ms |
– Main.SimonLeinen - 28 Feb 2006