Where does web server keep the session data exactly?

And in case of mobile phone internet access, how does the web server ide开发者_JAVA技巧ntify one visitor from another, through phone number?

It's stored on the server. PHP stores the session data internally depending on how you've configured session.save-path

See here for more info : http://us.php.net/manual/en/session.configuration.php#ini.session.save-path

Mobile phone internet access works just the same as any other HTTP access. The browser initiates a connection and the session is managed in the normal way. Phone numbers don't come into play at all

how does the web server identify one visitor from another, through phone number?

No they differentiate users from cookie , it saves data that will map client to session on server.