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?

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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

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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.