Sync vs. Async

A communication method like HTTP is not only point-to-point but also synchronous by default.

"Synchronous" communication means that the sender waits for the receiver to respond before continuing. It "blocks" the sender until the receiver is ready.

In asynchronous communication, the sender does not have to wait. It fires off the message and moves on with its duties.

As you've seen with our "pause" messages that our server sends to clients, it doesn't care if the clients are listening or not (they aren't even connected to their queues yet in our case!).