In the "reporting.realtime" middleware subscription, the network traffic stats have a "rate" associated with the interface which is always an exact duplicate of the total "bytes" counter from the system kernel/sysctl. I believe that rate field is supposed to be the difference between the current measurement and the previous measurement. If the measurements are 1s apart (which it appears that they are), this "rate" corresponds to the traffic through the interface in the last second which is useful for measuring/reporting current bandwidth.

Here is an example of the networking section from the event (latest 12-nightly).

"interfaces": {
"lo0": {
"received_bytes": 31349747295,
"received_bytes_rate": 31349747295,
"sent_bytes": 31349747295,
"sent_bytes_rate": 31349747295
},
"pflog0": {
"received_bytes": 0,
"received_bytes_rate": 0,
"sent_bytes": 0,
"sent_bytes_rate": 0
},
"wg0": {
"received_bytes": 165116383,
"received_bytes_rate": 165116383,
"sent_bytes": 4800742809,
"sent_bytes_rate": 4800742809
},
"xn0": {
"received_bytes": 12539694427,
"received_bytes_rate": 12539694427,
"sent_bytes": 34390604682,
"sent_bytes_rate": 34390604682
}
}