Is that right? Yes, it's almost right. Here it is in detail: host A sends data to host B1 host B1 sends data to host A host B2 sends data to hast A host A: iOS device host B1 + B2: external devices (not iOS) Is B1’s source port fixed? Yes it is. The ports for B1 + B2 are fixed. The port on A is not fixed, but I have to tell this used port to the other machines. My totally special requirement is to solve this issue with "only" one socket instance. One instance for streaming data to B1 and receive data from B2 or B1. I think with BSD sockets that is possible. Receive data from "any" and send data to specific machine. I know that I could solve this issue with NWListener who listen on port xyz for data. And send data after the connection handler setup is finished. But that would be 2 sockets in my opinion. Or you have other ideas or suggestions?

I don’t think there’s a way to make this work with Network framework. Okay, I already feared it :-) Host A can’t set up an NWListener to accept new connections from host B2 because the fixed port is already in use. Yepp ... that exactly right. My current workaround is to setup a connection (NWConnection) on an ephemeral system port (and tell this port to the other side). And setup an additional NWListener on a fixed port (e.g. 40.000). So it's possible to receive data from B1 and B2. But I think it's not really nice, it would be gracefully if I could solve this with one socket connection. But many thanks for your feedback and help.