This is also a common paradigm in networking called the client-server model. In this model, a server listens for connections. The client, knowing the address and port number that the server is listening on, establishes the connection by sending the first packet.
For example, the web server at
example.com listens on port
80 (HTTP) and port
443 (HTTPS). A web browser (client) must establish the connection by sending the first packet to the web server address and port.