# Given two or more nodes in a network, is it possible to determine the one-way link latencies between two nodes that share a bi-directional connection?

We already know that detecting the one-way latency between only two nodes is impossible.

However, if I have a number of nodes in the same subnet that all know about each other, can measure round-trip latencies (e.g. via ping), and can communicate with each other - and assuming link latencies do not change over time (for the simplicity of the problem) - is it possible to measure the individual up and down link speeds between two particular nodes within the subnet, potentially via coordination of one or more unrelated nodes in the network?

• A bi-directional connection consists of two uni-directional connections and each has a different latency (think of your upload/download speeds of your home network connection). Your "number of nodes" can be reduced to two nodes. Now you are back at the two robots of the link you refer to, implying that, no, you cannot. – Paul Ogilvie Oct 9 '19 at 14:55
• @PaulOgilvie So there's no way to do this by e.g. measuring the latencies of A<->C and B<->C in order to estimate the individual latencies of A<->B? That was never addressed in the link I mentioned. – Qix - MONICA WAS MISTREATED Oct 10 '19 at 16:19
• You cannot measure A<-->C. You have A-->C and C-->A. So you can measure A-->C-->B-->C-->A and then you have a roundtrip delay but you still do not know the delay of each individual connection. – Paul Ogilvie Oct 11 '19 at 9:00