There is no probe that can achieve this natively as a qos however it is possible to use the logmon probe to execute netstat to collect this data and then report this as a QOS value.
The netstat command to collect the number of active connections to a port is
netstat -na | find /c "port"
eg to collect port 48000
netstat -na | find /c "48000"
netstat -na | grep "48000" | wc -l
The instructions below show how to configure the logmon probe to run this command, generate QOS messages for the number of active connections to port 48000 and generate alarms when thresholds are breached
Note the example below is for windows, please change the netstat command for Unix \ LInux