How to calculate the size of data transferred between two machines in Ubuntu?

I have two computers. The first one is as a workstation. It runs the deep learning code and connects an AP by a wired connection. The second one is as a robot's computer. It sends the video and other information from other sensors and connects an AP by a LAN card. I'd like to know the data size of packets exchanged between them in real-time using commands in the terminal. How do I measure data they transfer to each other via the network? **Note:** I am using only local wireless LAN (no internet)