I ran into this in the domain of networking. Trying to deduce one-way path latency from the round-trip time ("ping") is impossible without further assumptions.

I ran into this in the domain of networking. Trying to deduce one-way path latency from the round-trip time ("ping") is impossible without further assumptions. You basically cannot understand if you are on a wire connection or if your uplink is via a sat by looking at just the ping output. You can try an bounce ping off multiple servers, relay pings and gather RTT properties over any graph path that includes your node and test servers, and yet you will always come one equation short for solving the linear system you'd end up with. -- However -- If you make an assumption about some property of some path, then - boom - you can find the one-way latency for any edge on the graph. For example, if you have two test servers that sit on a backbone, you can assume the path latency between them is about the same either way. This gives you an extra linear for the system and this in turn lets you calculate the one-way latency between you and either of these servers. It's a pretty neat problem. Makes you think, laterally.