As Wikipedia explains:
HTTP persistent connection, also called HTTP keep-alive, or HTTP connection reuse, is the idea of using a single TCP connection to send and receive multiple HTTP requests/responses, as opposed to opening a new connection for every single request/response pair. The newer SPDY protocol uses the same idea and takes it further to allow multiple concurrent requests/responses to be multiplexed over a single connection.
Note: I assume you have adequate knowledge of handling your server & server settings & you are well versed in your field
You can put following code in your .htaceess file which is available in your root of your server’s html folder