Request-response

The classical server architecture is heavily based on request-response to communicate. A client sends a request to a remote server and the server processes it and returns a response.

This communication pattern has been prevalent since the era of mainframes and works in an analog manner as software communicates internally with a library, but over a network. The software calls a library and receives a response from it.

An important element is the time delay between the sending of the request and the reception of the response. Internally, it is rare that a call takes more than a couple of milliseconds, but for a network, it may be measured in hundreds of milliseconds and seconds, very commonly.

Network calls are very dependent on where the server is located. A call within the same data center will be fast, perhaps taking less than 100 milliseconds, while a connection to an external API will likely take close to a second or more.

Times will...