Editing Network access server (section)

==Examples==
The above translates into different implementations for different uses. Here are some examples.

*An [[Internet service provider]] which provides network access via common modem or modem-like devices (be it [[PSTN]], [[DSL]], [[cable modem|cable]] or [[GPRS]]/[[UMTS]]) can have one or more NAS (network access server) devices which accept [[Point-to-Point Protocol|PPP]], [[PPPoE]] or [[PPTP]] connections, checking credentials and recording accounting data via back-end [[RADIUS]] servers, and allowing users access through that connection.
* The [[captive portal]] mechanism used by many [[WiFi]] providers: a user wants to access the Internet and opens a [[web browser|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 protocol|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.
*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 calling|long distance]] access or a [[telephone card]] has minutes left.