Point-to-Point Protocol

Today no one uses dumb terminals or terminal emulators to connect to an individual computer. Instead we all use our modems to connect to an Internet Service Provider (ISP), and the ISP connects us into the Internet. The Internet lets us connect to any machine in the world. Because of the relationship between your computer, the ISP and the Internet, it is no longer appropriate to send individual characters. Instead, your modem is routing TCP/IP packets between you and your ISP.

The standard technique for routing these packets through your modem is called PPP or the Point-to-Point Protocol. The basic idea is simple - your computer's TCP/IP stack forms its TCP/IP datagrams normally, but then the datagrams are handed to the modem for transmission. The ISP receives each datagram and routes it appropriately onto the Internet. The same thing happens to get data from the ISP to your computer.