CCNA, CCNP, MCSA, CCNA Final Exam, All Answer Test Module With 100/100

All HTTP responses require the client to initiate them, even those made using AJAX. But GMail's chat feature is able to receive messages from other users, even when I'm just sitting in my comfy computer chair watching but not interacting with the browser. How did they do it?

There are 1 on 1 live chat. Two solutions: 1) I store every message into database and with jQuery's help I check if there is a new message in database every second. Of course I use cache either. If there is, we give that message.