The HTTP protocol is based on a client/server architecture, where clients know what they want to do and request documents (or data or services) from a server. The client is active, the server is reactive. For this purpose, HTTP is built around a simple Request/Response mechanism. Clients connect to servers, pose their requests, and servers respond with one response per request. The connection can be dropped by any of the clients or servers:
Request/Response pattern in HTTP
Most HTTP servers today allow for multiple requests over the same connection to improve performance. This feature, called persistent connections, was not specified in HTTP 1.0. Support for it is required in HTTP 1.1, unless explicitly disabled, but only one request can be served at a time. In HTTP 2.0 multiple requests can be processed simultaneously over the same connection.