Stop Simulink Model until command received by tcp/ip?

I have two models. One in Simulink and one extern software. Those two should communicate by TCP/IP. I would like to execute my Simulink Model for e.g. 3 Timesteps. Then send an TCP/IP Signal to my extern software, and wait for the response. When I get an response over TCP/IP , the Simulink Model should continue the next 3 Timesteps and send again an signal to the extern software and so on...

How can I implement this problem in Simulink? On the one hand how can I pause the Simulink Simulation until the response came back? And on the other hand how can I establish this kind of connection? Do I have to use two separate TCP/IP connections or is this possible with one single connection?

Thanks in advance