How to push data from WCF service to client applications

Question

Well, I haven't done anything similar to this. so I am stuck at this problem.

 

I have a service called LoadBalancer, that sends data to its client depending on the algorithm, so when the algorithm decide I should send data to a specific worker. 

 

I researched a bit more on this topic and found Duplex Communication should help me solve, but I've got a few questions regarding Duplex Comm.

 

From what I found online, it's mostly client asks the server and with callback, we can send the data, but I do not know which client will be receiving the data, because I'll have multiple instances of them. So is there a way server to send first the data, and client to send response to it?