What is the meaning of “incomingPacketStreamStats. PacketRate“ and "outgoingPacketStreamStats packetRate ” in jvb "stress_level" statistics?

We intend to take secondary development, but now the problems on load balancing, want to know JVB “stress_leavel” the principle of calculation, there are two values “incomingPacketStreamStats. PacketRate” and “outgoingPacketStreamStats PacketRate” the principle of can’t understand it. Is there any relevant document to explain?