User's Manual

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266 Installation and User Guide: Airgo Access Point
The station associates to the AP. The AP allows the station to obtain a DHCP based IP address and
allows ARP and DNS queries. All other traffic is blocked. Web traffic is blocked and redirected to
the ELPS. The ELPS provides web pages to authenticate users and subsequently signals the AP to
allow the station access to a broader set of IP addresses (the Internet).
The web server (ELPS) is also able to disconnect any of the previously connected stations. The
signaling from the web server to the AP includes a disconnect request. The disconnect request can
be used to stop billed connection time at a hot spot. This is often implemented by providing a status
web window that displays the users time on-line with a button to provide the logout. The disconnect
can also be sent directly from the server to the AP to provide a forced disconnection of the user
based on the management functionality in the web server.
The process to enable access (from the ELPS to the AP) is analogous to purchasing a ticket and
then entering a theater. The guest station represents the theater patron, the external authentication
web server represents the box office, and the AP represents the ticket taker.
Upon entering the theater, the patron is first directed to the box office and presents credentials in
order to collect tickets (money or identification for pre-ordered tickets). The patron then takes the
ticket to the ticket taker, who validates the ticket and permits entrance. Correct validation includes
a check of the timestamp (date and time of performance) and confirmation of the type of
performance. In effect, the ticket taker verifies that the ticket has been issued by the box office.
Detailed Signaling Description and API
The application programming interface (API) between the ELPS and the AP supports the following
uses:
• Connect Sequence: Capture unauthenticated users and subsequently connect them after a valid
authentication
• User Initiated Disconnect: Disconnect a station based on a user request to logout (STA
Disconnect)
• Station Forced Disconnect: Force a disconnect from the ELPS (STA Forced Disconnect)
Connect Sequence
The signaling flow for a station associating with the network for the first time is illustrated in
Figure 1.