The participants, usually a client and a server, need to be available throughout execution of the application. So does the network connection. Message queuing systems take a different approach. They separate application communication from the network operations. At the application level they are connectionless.
Applications send data by placing messages on queues.
They receive data by reading messages from queues. These queuing operations are local. The don t require any network connection in themselves. In a separate operation, the message queuing system moves messages between queues, across any intervening networks. Moving the messages does require a connection, of course.