what this function in fact does? It only compares host from dispatcher list and $si ? or it compares with source port as well ?

I'm distributing traffic across multiple gateways with dispatcher module, these gateways create another leg and send it back to proxy. I would like to compare it with my dispatcher list if the source IP of the request is one of the dispatcher list. 

So I cannot use this function, right? Any other functions that can do something similar? 

Mino