Service Announcements for Hot-Spots: Enabling Automated Access and Provider Selection for Voice over WiFi

Bibliographic Entry Jörg Ott, Dirk Kutscher; SIP Voice Services for Intermittently Connected Users in Wireless Networks ; Upperside Wi-Fi Voice Conference 2005; May 2005

WLAN hot-spots are a well established as powerful and widely available access technology that is increasingly used for voice communications. While, until recently, laptop computers dominated the scene of mobile users, increased battery lifetimes render stand-alone WLAN hardware phones (but also PDAs) interesting alternatives. Nevertheless, accessing WLAN hot-spots remains a tedious task until now: determining the hot-spot access parameters, manually configuring the user device, and/or requiring web-based authentication with wireless ISP (WISP) are already cumbersome to handle on a laptop. But the various interfaces are much harder to deal with on small scale devices such as PDAs and may become entirely impractical on embedded WLAN IP phones. In particular, any need for a user's manual intervention is inadequate at best for providing voice services, even in geographically restricted areas.

Instead, a user device must---besides IP layer auto-configuration---be capable of determining available hot-spots and WISPs automatically, select an appropriate service provider based upon the user's subscriptions and her personal preferences (policies), and automatically authenticate with the chosen WISP to gain access to the Internet. Manual user intervention should only be required if no automatic selection is possible and may involve "alerting" the user that a WLAN is available but not yet usable. While many different authentication schemes for WLAN hot-spots exist, the Wi-Fi Alliance has defined conventions for the Universal Access Method (UAM) for web-based authentication. Unfortunately, only a few hot-spots actually adhere to these conventions and, in addition, UAM does not cover scenarios in which a single hot-spot is serviced by multiple WISPs leaving the choice up to the user. We have implemented an automated authentication mechanism for WLAN hot-spots that are (roughly) UAM-compliant. While this our tool set operates successfully in many cases, we have also identified a number of potential failure scenarios: JavaScript in login web pages, login pages that are not easy to identify as such, and multiple forms with with several WISPs that are hard to relate to the authentication process, to name just a few. While strict adherence to the UAM conventions would solve some of these problems, the basic approach of parsing information intended for human perception remains error-prone.

The Wi-Fi Alliance has also specified an XML-based service provider announcement scheme that can be distributed (e.g., using multicast service announcement protocols) within WLAN hot-spots and convey machine-readable information to the mobile users---which is unfortunately not really widespread. Such access service announcements would allow mobile devices to precisely identify WISPs without the need for second-guessing and ensure quick establishment of WLAN access, at minimal overhead. Heuristics-based automated authentication tools as described above may be used as a fallback when no announcements are received. Using a suitable description and distribution framework, this set of basic access information may be augmented by further announcements about additional available services. Local information resources may be advertised as may be third party services such as streaming media and local IP telephony services (e.g., gateways, available QoS options, etc.). Particularly users of WLAN IP phones will benefit from such announcements as they will provide quick and error-free enhanced auto-configuration and improve perceived service availability.