[Users] TLS: what is encrypted in TLS?

Dear all, Thank you for this chance. All, I have tried to learn about how can TLS can secure communication in VoIP. I must to understand it in order to responsible my openser server (working) with TLS to my lecturer. But, I have still doubt. Actually, what is encrypted in TLS system so the communication become secure? Does it encrypt the data (voise packet)? or The traffic (so the sniffer can not get the data? OR anything else? I do hope anybody can help me :) Thanks, Ferianto Note: I cryptography tutorials, I read that the cryptography system secure the message (text) by encrypting it using public key and private key. So, How about TLS in VoIP? --------------------------------- Everyone is raving about the all-new Yahoo! Mail.