3. AAA and remote connection via dial-up network

When a user wants to access the Internet, or even his company's Intranet, from a dial-up network (such as PSTN, ISDN, GSM or GPRS), he needs to connect a modem between his computer and the dial-up network. He then dials a specific telephone number provided by his Internet Service Provider (ISP). This number gives access to an ISP device called a NAS (Network Access Server). To access the Internet as a private individual, he'll need to connect to his own ISP subscription. If he wants to access his Intranet, he will have to contact his company's ISP, which will then identify him as an employee of a certain corporate client.

All exchanges between the NAS and the modem are carried out using the Point-to-Point Protocol (PPP)