| Abstract |
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.
|
