HTTP persistent connection

The newer HTTP/2 protocol uses the same idea and takes it further to allow multiple concurrent requests/responses to be multiplexed over a single connection.

using HTTP/1.0, started to add an unofficial extension (to the protocol) named "keep-alive" in order to allow the reuse of a connection for multiple requests/responses.

Since 1997, the various versions of HTTP/1.1 specifications acknowledged the usage of this unofficial extension and included a few caveats regarding the interoperability between HTTP/1.0 (keep-alive) and HTTP/1.1 clients / servers.

[12] To solve this problem, HTTP 1.1 introduced a chunked transfer coding that defines a last-chunk bit.

According to RFC 7230, section 6.4, "a client ought to limit the number of simultaneous open connections that it maintains to a given server".

[15] A server should send a 408 Request Timeout status code to the client immediately before closing the connection.

All modern web browsers including Google Chrome, Firefox, Internet Explorer (since 4.01), Opera (since 4.0)[17] and Safari use persistent connections.