When we setup external data in the test case, there isn't’t any counter is related to the data traffic (e.g. L3 Client tab etc.), we already have an enhancement request for this case.
So far, there is a workaround. Just add “Data Traffic” to the test case and then add a limited transaction DMF like a UDP or PING with 1 transaction. External Data requires a remote NH, so you can just use the same remote NH as the external data since we don't really care whether the limited transaction UDP or PING is responded to correctly. Then you run the test again, you are able to see the counters of data traffic, e.g. L3 Client, L4 Client etc. When you saw the number of pps/bps from the counters, you need to minus the packets of remote network host from “Data Traffic”.