Questions about RadPerf-u14.04

I'm using RadPerf-u14.04 on Ubuntu 14.04 machine. Why is it that I cannot use -n together with -p? Does the "Packets/s" means Requests/seconds? If so, why is it that when I set -n to 50, the packet/sec is always less than 5, it only goes higher after using -p. Thanks, Jim Well Balatero, Cleversoft, Inc.