How to I calcul the latency on a network

The latency is the time the packet is sent from A to B and come back to A.

Since I'm not sure if the time it take to send a packet from a to b will be the same as the b to a, I will say there is a ping/pong.

There is the ping and the pong. The ping is the packet sent to the target and the pong is the packet sent to the original sender.

Both add make the latency.

But to know who is lagging, or what is the latency of the ping and the pong. I need to have two identical computer set on the same time. Same time on 0.000

The time will be send with the packet to the target. And with the difference on the target it is possible to calcul the ping. Than a packet will be send from the target and the time will be calcul by the sender.

It is possible that the pong is useless because there is always no difference. I'll know later.

Note that the pong in this story is for monitoring and troubleshooting for the network guys.
For the games, the latency of both should be enough.