<P> The above translates into different implementations for different uses . Here are some examples . </P> <Ul> <Li> An Internet service provider which provides network access via common modem or modem - like devices (be it PSTN, DSL, cable or GPRS / UMTS) can have one or more NAS (network access server) devices which accept PPP, PPPoE or PPTP connections, checking credentials and recording accounting data via back - end RADIUS servers, and allowing users access through that connection . </Li> <Li> The captive portal mechanism used by many WiFi providers: a user wants to access the Internet and opens a browser . The NAS detects that the user is not currently authorized to have access to the Internet, so the NAS prompts the user for their username and password . The user supplies them and sends them back to the NAS . The NAS then uses the RADIUS protocol to connect to an AAA server and passes off the username and password . The RADIUS server searches through its resources and finds that the credentials are valid and notifies the NAS that it should grant the access . The NAS then grants the user access to the Internet . </Li> <Li> Another use of a NAS would be in voice over IP (VoIP). However, instead of using a username and password, many times a phone number or IP Address are used . If the phone number is a valid customer then the call can be completed . Other uses might be to verify whether a phone number has long distance access or a telephone card has minutes left . </Li> </Ul> <Li> An Internet service provider which provides network access via common modem or modem - like devices (be it PSTN, DSL, cable or GPRS / UMTS) can have one or more NAS (network access server) devices which accept PPP, PPPoE or PPTP connections, checking credentials and recording accounting data via back - end RADIUS servers, and allowing users access through that connection . </Li> <Li> The captive portal mechanism used by many WiFi providers: a user wants to access the Internet and opens a browser . The NAS detects that the user is not currently authorized to have access to the Internet, so the NAS prompts the user for their username and password . The user supplies them and sends them back to the NAS . The NAS then uses the RADIUS protocol to connect to an AAA server and passes off the username and password . The RADIUS server searches through its resources and finds that the credentials are valid and notifies the NAS that it should grant the access . The NAS then grants the user access to the Internet . </Li>

How to access the server on a network