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

Updated

I have two computers.

The first one is as a workstation. It runs the deep learning code and connects an AP by a wired.

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 that exchanges between them in real-time using the command in the terminal.

How do I measure data they transfer to each other via the Network for a specific Network?

Here, I meant by the specific Network (the robot's computer)

Can I know how much the robot's computer sends data to the workstation? Meanwhile, how much data the workstation sends to the robot's computer (in two directions)

Note: I am using the wireless and the wired without internet (no internet)

The simplest (and oldest) tool to do this would be netstat -i but this lists only total traffic on each interface, not trafic to specific hosts.

The link provided in comments above points to an answer in this question; the answers there include a fairly comprehensive list of tools to view network traffic in real time.

However, one answer more specific to your question is not there. It is possible using iptables to set up a firewall rule whose sole purpose is to search for specific traffic, such as traffic between the current host and another host, and count it in bytes and packets. So if the above tools give answers that are too general, iptables is where you want to look next.