[…] the browser is always the entity initiating the request. It is never the server (though some mechanisms have been added over the years to simulate server-initiated messages).
in order to mitigate this flaw (each http request requiring a new TCP connection), HTTP/1.1 introduced pipelining (which proved difficult to implement) and persistent connections: the underlying TCP connection can be partially controlled using the Connection header. HTTP/2 went a step further by multiplexing messages over a single connection, helping keep the connection warm and more efficient.
